Changeset 3294 for trunk/DOC/TexFiles/Chapters
- Timestamp:
- 2012-01-28T17:44:18+01:00 (12 years ago)
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- trunk/DOC/TexFiles/Chapters
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- 24 edited
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trunk/DOC/TexFiles/Chapters/Abstracts_Foreword.tex
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r2541 r3294 8 8 \vspace{-40pt} 9 9 10 \small{ 10 {\small 11 11 The ocean engine of NEMO (Nucleus for European Modelling of the Ocean) is a primitive 12 12 equation model adapted to regional and global ocean circulation problems. It is intended to -
trunk/DOC/TexFiles/Chapters/Annex_A.tex
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r2282 r3294 13 13 % Chain rule 14 14 % ================================================================ 15 \section{ Chain rule of $s-$coordinate}15 \section{The chain rule for $s-$coordinates} 16 16 \label{Apdx_A_continuity} 17 17 18 In order to establish the set of Primitive Equation in curvilinear $s -$coordinates18 In order to establish the set of Primitive Equation in curvilinear $s$-coordinates 19 19 ($i.e.$ an orthogonal curvilinear coordinate in the horizontal and an Arbitrary Lagrangian 20 20 Eulerian (ALE) coordinate in the vertical), we start from the set of equations established … … 62 62 % continuity equation 63 63 % ================================================================ 64 \section{Continuity Equation in $s-$coordinate }64 \section{Continuity Equation in $s-$coordinates} 65 65 \label{Apdx_A_continuity} 66 66 … … 128 128 Here, $w$ is the vertical velocity relative to the $z-$coordinate system. 129 129 Introducing the dia-surface velocity component, $\omega $, defined as 130 the v elocity relative to the moving $s-$surfaces and normal to them:130 the volume flux across the moving $s$-surfaces per unit horizontal area: 131 131 \begin{equation} \label{Apdx_A_w_s} 132 132 \omega = w - w_s - \sigma _1 \,u - \sigma _2 \,v \\ … … 429 429 This formulation of the pressure gradient is characterised by the appearance of a term depending on the 430 430 the sea surface height only (last term on the right hand side of expression \eqref{Apdx_A_grad_p}). 431 This term will be abusively named \textit{surface pressure gradient} whereas the first term will be named 431 This term will be loosely termed \textit{surface pressure gradient} 432 whereas the first term will be termed the 432 433 \textit{hydrostatic pressure gradient} by analogy to the $z$-coordinate formulation. 433 434 In fact, the the true surface pressure gradient is $1/\rho_o \nabla (\rho \eta)$, and … … 451 452 To sum up, in a curvilinear $s$-coordinate system, the vector invariant momentum equation 452 453 solved by the model has the same mathematical expression as the one in a curvilinear 453 $z-$coordinate, butthe pressure gradient term :454 $z-$coordinate, except for the pressure gradient term : 454 455 \begin{subequations} \label{Apdx_A_dyn_vect} 455 456 \begin{multline} \label{Apdx_A_PE_dyn_vect_u} … … 495 496 \end{subequations} 496 497 Both formulation share the same hydrostatic pressure balance expressed in terms of 497 hydrostatic pressure and density an malies, $p_h'$ and $d=( \frac{\rho}{\rho_o}-1 )$:498 hydrostatic pressure and density anomalies, $p_h'$ and $d=( \frac{\rho}{\rho_o}-1 )$: 498 499 \begin{equation} \label{Apdx_A_dyn_zph} 499 500 \frac{\partial p_h'}{\partial k} = - d \, g \, e_3 … … 502 503 It is important to realize that the change in coordinate system has only concerned 503 504 the position on the vertical. It has not affected (\textbf{i},\textbf{j},\textbf{k}), the 504 orthogonal curvilinear set of unit vector . ($u$,$v$) are always horizontal velocities505 orthogonal curvilinear set of unit vectors. ($u$,$v$) are always horizontal velocities 505 506 so that their evolution is driven by \emph{horizontal} forces, in particular 506 507 the pressure gradient. By contrast, $\omega$ is not $w$, the third component of the velocity, 507 but the dia-surface velocity component, $i.e.$ the v elocity relative tothe moving508 $s -$surfaces and normal to them.508 but the dia-surface velocity component, $i.e.$ the volume flux across the moving 509 $s$-surfaces per unit horizontal area. 509 510 510 511 -
trunk/DOC/TexFiles/Chapters/Annex_B.tex
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r2282 r3294 16 16 \label{Apdx_B_1} 17 17 18 19 In the $z$-coordinate, the horizontal/vertical second order tracer diffusion operator18 \subsubsection*{In z-coordinates} 19 In $z$-coordinates, the horizontal/vertical second order tracer diffusion operator 20 20 is given by: 21 21 \begin{eqnarray} \label{Apdx_B1} 22 &D^T = \frac{1}{e_1 \, e_2} \left[ 23 \left. \frac{\partial}{\partial i} \left( \frac{e_2}{e_1}A^{lT} \;\left. \frac{\partial T}{\partial i} \right|_z \right) \right|_z \right. 22 &D^T = \frac{1}{e_1 \, e_2} \left[ 23 \left. \frac{\partial}{\partial i} \left( \frac{e_2}{e_1}A^{lT} \;\left. \frac{\partial T}{\partial i} \right|_z \right) \right|_z \right. 24 24 \left. 25 + \left. \frac{\partial}{\partial j} \left( \frac{e_1}{e_2}A^{lT} \;\left. \frac{\partial T}{\partial j} \right|_z \right) \right|_z \right] 25 + \left. \frac{\partial}{\partial j} \left( \frac{e_1}{e_2}A^{lT} \;\left. \frac{\partial T}{\partial j} \right|_z \right) \right|_z \right] 26 26 + \frac{\partial }{\partial z}\left( {A^{vT} \;\frac{\partial T}{\partial z}} \right) 27 27 \end{eqnarray} 28 28 29 In the $s$-coordinate, we defined the slopes of $s$-surfaces, $\sigma_1$ and 30 $\sigma_2$ by \eqref{Apdx_A_s_slope} and the vertical/horizontal ratio of diffusion 29 \subsubsection*{In generalized vertical coordinates} 30 In $s$-coordinates, we defined the slopes of $s$-surfaces, $\sigma_1$ and 31 $\sigma_2$ by \eqref{Apdx_A_s_slope} and the vertical/horizontal ratio of diffusion 31 32 coefficient by $\epsilon = A^{vT} / A^{lT}$. The diffusion operator is given by: 32 33 33 34 \begin{equation} \label{Apdx_B2} 34 D^T = \left. \nabla \right|_s \cdot 35 D^T = \left. \nabla \right|_s \cdot 35 36 \left[ A^{lT} \;\Re \cdot \left. \nabla \right|_s T \right] \\ 36 37 \;\;\text{where} \;\Re =\left( {{\begin{array}{*{20}c} 37 38 1 \hfill & 0 \hfill & {-\sigma _1 } \hfill \\ 38 39 0 \hfill & 1 \hfill & {-\sigma _2 } \hfill \\ 39 {-\sigma _1 } \hfill & {-\sigma _2 } \hfill & {\varepsilon +\sigma _1 40 {-\sigma _1 } \hfill & {-\sigma _2 } \hfill & {\varepsilon +\sigma _1 40 41 ^2+\sigma _2 ^2} \hfill \\ 41 42 \end{array} }} \right) … … 43 44 or in expanded form: 44 45 \begin{subequations} 45 \begin{align*} {\begin{array}{*{20}l} 46 D^T=& \frac{1}{e_1\,e_2\,e_3 }\;\left[ {\ \ \ \ e_2\,e_3\,A^{lT} \;\left. 46 \begin{align*} {\begin{array}{*{20}l} 47 D^T=& \frac{1}{e_1\,e_2\,e_3 }\;\left[ {\ \ \ \ e_2\,e_3\,A^{lT} \;\left. 47 48 {\frac{\partial }{\partial i}\left( {\frac{1}{e_1}\;\left. {\frac{\partial T}{\partial i}} \right|_s -\frac{\sigma _1 }{e_3 }\;\frac{\partial T}{\partial s}} \right)} \right|_s } \right. \\ 48 49 &\qquad \quad \ \ \ +e_1\,e_3\,A^{lT} \;\left. {\frac{\partial }{\partial j}\left( {\frac{1}{e_2 }\;\left. {\frac{\partial T}{\partial j}} \right|_s -\frac{\sigma _2 }{e_3 }\;\frac{\partial T}{\partial s}} \right)} \right|_s \\ 49 &\qquad \quad \ \ \ + e_1\,e_2\,A^{lT} \;\frac{\partial }{\partial s}\left( {-\frac{\sigma _1 }{e_1 }\;\left. {\frac{\partial T}{\partial i}} \right|_s -\frac{\sigma _2 }{e_2 }\;\left. {\frac{\partial T}{\partial j}} \right|_s } \right. 50 \left. {\left. {+\left( {\varepsilon +\sigma _1^2+\sigma _2 ^2} \right)\;\frac{1}{e_3 }\;\frac{\partial T}{\partial s}} \right)\;\;} \right] 51 \end{array} } 50 &\qquad \quad \ \ \ + e_1\,e_2\,A^{lT} \;\frac{\partial }{\partial s}\left( {-\frac{\sigma _1 }{e_1 }\;\left. {\frac{\partial T}{\partial i}} \right|_s -\frac{\sigma _2 }{e_2 }\;\left. {\frac{\partial T}{\partial j}} \right|_s } \right. 51 \left. {\left. {+\left( {\varepsilon +\sigma _1^2+\sigma _2 ^2} \right)\;\frac{1}{e_3 }\;\frac{\partial T}{\partial s}} \right)\;\;} \right] 52 \end{array} } 52 53 \end{align*} 53 54 \end{subequations} 54 55 55 Equation \eqref{Apdx_B2} is obtained from \eqref{Apdx_B1} without any 56 additional assumption. Indeed, for the special case $k=z$ and thus $e_3 =1$, 57 we introduce an arbitrary vertical coordinate $s = s (i,j,z)$ as in Appendix~\ref{Apdx_A} 58 and use \eqref{Apdx_A_s_slope} and \eqref{Apdx_A_s_chain_rule}. 59 Since no cross horizontal derivative $\partial _i \partial _j $ appears in 60 \eqref{Apdx_B1}, the ($i$,$z$) and ($j$,$z$) planes are independent. 61 The derivation can then be demonstrated for the ($i$,$z$)~$\to$~($j$,$s$) 56 Equation \eqref{Apdx_B2} is obtained from \eqref{Apdx_B1} without any 57 additional assumption. Indeed, for the special case $k=z$ and thus $e_3 =1$, 58 we introduce an arbitrary vertical coordinate $s = s (i,j,z)$ as in Appendix~\ref{Apdx_A} 59 and use \eqref{Apdx_A_s_slope} and \eqref{Apdx_A_s_chain_rule}. 60 Since no cross horizontal derivative $\partial _i \partial _j $ appears in 61 \eqref{Apdx_B1}, the ($i$,$z$) and ($j$,$z$) planes are independent. 62 The derivation can then be demonstrated for the ($i$,$z$)~$\to$~($j$,$s$) 62 63 transformation without any loss of generality: 63 64 64 \begin{subequations} 65 \begin{align*} {\begin{array}{*{20}l} 66 D^T&=\frac{1}{e_1\,e_2} \left. {\frac{\partial }{\partial i}\left( {\frac{e_2}{e_1}A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_z } \right)} \right|_z 65 \begin{subequations} 66 \begin{align*} {\begin{array}{*{20}l} 67 D^T&=\frac{1}{e_1\,e_2} \left. {\frac{\partial }{\partial i}\left( {\frac{e_2}{e_1}A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_z } \right)} \right|_z 67 68 +\frac{\partial }{\partial z}\left( {A^{vT}\;\frac{\partial T}{\partial z}} \right) \\ 69 \\ 70 % 71 &=\frac{1}{e_1\,e_2 }\left[ {\left. {\;\frac{\partial }{\partial i}\left( {\frac{e_2}{e_1}A^{lT}\;\left( {\left. {\frac{\partial T}{\partial i}} \right|_s 72 -\frac{e_1\,\sigma _1 }{e_3 }\frac{\partial T}{\partial s}} \right)} \right)} \right|_s } \right. \\ 73 & \qquad \qquad \left. { -\frac{e_1\,\sigma _1 }{e_3 }\frac{\partial }{\partial s}\left( {\frac{e_2 }{e_1 }A^{lT}\;\left. {\left( {\left. {\frac{\partial T}{\partial i}} \right|_s -\frac{e_1 \,\sigma _1 }{e_3 }\frac{\partial T}{\partial s}} \right)} \right|_s } \right)\;} \right] 74 \shoveright{ +\frac{1}{e_3 }\frac{\partial }{\partial s}\left[ {\frac{A^{vT}}{e_3 }\;\frac{\partial T}{\partial s}} \right]} \qquad \qquad \qquad \\ 75 \\ 76 % 77 &=\frac{1}{e_1 \,e_2 \,e_3 }\left[ {\left. {\;\;\frac{\partial }{\partial i}\left( {\frac{e_2 \,e_3 }{e_1 }A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s } \right)} \right|_s -\left. {\frac{e_2 }{e_1}A^{lT}\;\frac{\partial e_3 }{\partial i}} \right|_s \left. {\frac{\partial T}{\partial i}} \right|_s } \right. \\ 78 & \qquad \qquad \quad \left. {-e_3 \frac{\partial }{\partial i}\left( {\frac{e_2 \,\sigma _1 }{e_3 }A^{lT}\;\frac{\partial T}{\partial s}} \right)} \right|_s -e_1 \,\sigma _1 \frac{\partial }{\partial s}\left( {\frac{e_2 }{e_1 }A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s } \right) \\ 79 & \qquad \qquad \quad \shoveright{ -e_1 \,\sigma _1 \frac{\partial }{\partial s}\left( {-\frac{e_2 \,\sigma _1 }{e_3 }A^{lT}\;\frac{\partial T}{\partial s}} \right)\;\,\left. {+\frac{\partial }{\partial s}\left( {\frac{e_1 \,e_2 }{e_3 }A^{vT}\;\frac{\partial T}{\partial s}} \right)\quad} \right] }\\ 80 \end{array} } \\ 81 % 82 {\begin{array}{*{20}l} 83 \intertext{Noting that $\frac{1}{e_1} \left. \frac{\partial e_3 }{\partial i} \right|_s = \frac{\partial \sigma _1 }{\partial s}$, it becomes:} 84 % 85 & =\frac{1}{e_1\,e_2\,e_3 }\left[ {\left. {\;\;\;\frac{\partial }{\partial i}\left( {\frac{e_2\,e_3 }{e_1}\,A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s } \right)} \right|_s \left. -\, {e_3 \frac{\partial }{\partial i}\left( {\frac{e_2 \,\sigma _1 }{e_3 }A^{lT}\;\frac{\partial T}{\partial s}} \right)} \right|_s } \right. \\ 86 & \qquad \qquad \quad -e_2 A^{lT}\;\frac{\partial \sigma _1 }{\partial s}\left. {\frac{\partial T}{\partial i}} \right|_s -e_1 \,\sigma_1 \frac{\partial }{\partial s}\left( {\frac{e_2 }{e_1 }A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s } \right) \\ 87 & \qquad \qquad \quad\shoveright{ \left. { +e_1 \,\sigma _1 \frac{\partial }{\partial s}\left( {\frac{e_2 \,\sigma _1 }{e_3 }A^{lT}\;\frac{\partial T}{\partial s}} \right)+\frac{\partial }{\partial s}\left( {\frac{e_1 \,e_2 }{e_3 }A^{vT}\;\frac{\partial T}{\partial z}} \right)\;\;\;} \right] }\\ 68 88 \\ 69 \allowdisplaybreaks 70 &=\frac{1}{e_1\,e_2 }\left[ {\left. {\;\frac{\partial }{\partial i}\left( {\frac{e_2}{e_1}A^{lT}\;\left( {\left. {\frac{\partial T}{\partial i}} \right|_s 71 -\frac{e_1\,\sigma _1 }{e_3 }\frac{\partial T}{\partial s}} \right)} \right)} \right|_s } \right. \\ 72 & \qquad \qquad \left. { -\frac{e_1\,\sigma _1 }{e_3 }\frac{\partial }{\partial s}\left( {\frac{e_2 }{e_1 }A^{lT}\;\left. {\left( {\left. {\frac{\partial T}{\partial i}} \right|_s -\frac{e_1 \,\sigma _1 }{e_3 }\frac{\partial T}{\partial s}} \right)} \right|_s } \right)\;} \right] 73 \shoveright{ +\frac{1}{e_3 }\frac{\partial }{\partial s}\left[ {\frac{A^{vT}}{e_3 }\;\frac{\partial T}{\partial s}} \right]} \qquad \qquad \qquad \\ 74 \\ 75 \allowdisplaybreaks 76 &=\frac{1}{e_1 \,e_2 \,e_3 }\left[ {\left. {\;\;\frac{\partial }{\partial i}\left( {\frac{e_2 \,e_3 }{e_1 }A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s } \right)} \right|_s -\left. {\frac{e_2 }{e_1}A^{lT}\;\frac{\partial e_3 }{\partial i}} \right|_s \left. {\frac{\partial T}{\partial i}} \right|_s } \right. \\ 77 & \qquad \qquad \quad \left. {-e_3 \frac{\partial }{\partial i}\left( {\frac{e_2 \,\sigma _1 }{e_3 }A^{lT}\;\frac{\partial T}{\partial s}} \right)} \right|_s -e_1 \,\sigma _1 \frac{\partial }{\partial s}\left( {\frac{e_2 }{e_1 }A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s } \right) \\ 78 & \qquad \qquad \quad \shoveright{ -e_1 \,\sigma _1 \frac{\partial }{\partial s}\left( {-\frac{e_2 \,\sigma _1 }{e_3 }A^{lT}\;\frac{\partial T}{\partial s}} \right)\;\,\left. {+\frac{\partial }{\partial s}\left( {\frac{e_1 \,e_2 }{e_3 }A^{vT}\;\frac{\partial T}{\partial s}} \right)\quad} \right] }\\ 79 \end{array} } \\ 80 {\begin{array}{*{20}l} 81 % 82 \allowdisplaybreaks 83 \intertext{Noting that $\frac{1}{e_1} \left. \frac{\partial e_3 }{\partial i} \right|_s = \frac{\partial \sigma _1 }{\partial s}$, it becomes:} 84 % 85 & =\frac{1}{e_1\,e_2\,e_3 }\left[ {\left. {\;\;\;\frac{\partial }{\partial i}\left( {\frac{e_2\,e_3 }{e_1}\,A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s } \right)} \right|_s \left. -\, {e_3 \frac{\partial }{\partial i}\left( {\frac{e_2 \,\sigma _1 }{e_3 }A^{lT}\;\frac{\partial T}{\partial s}} \right)} \right|_s } \right. \\ 86 & \qquad \qquad \quad -e_2 A^{lT}\;\frac{\partial \sigma _1 }{\partial s}\left. {\frac{\partial T}{\partial i}} \right|_s -e_1 \,\sigma_1 \frac{\partial }{\partial s}\left( {\frac{e_2 }{e_1 }A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s } \right) \\ 87 & \qquad \qquad \quad\shoveright{ \left. { +e_1 \,\sigma _1 \frac{\partial }{\partial s}\left( {\frac{e_2 \,\sigma _1 }{e_3 }A^{lT}\;\frac{\partial T}{\partial s}} \right)+\frac{\partial }{\partial s}\left( {\frac{e_1 \,e_2 }{e_3 }A^{vT}\;\frac{\partial T}{\partial z}} \right)\;\;\;} \right] }\\ 88 \\ 89 &=\frac{1}{e_1 \,e_2 \,e_3 } \left[ {\left. {\;\;\;\frac{\partial }{\partial i} \left( {\frac{e_2 \,e_3 }{e_1 }A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s } \right)} \right|_s \left. {-\frac{\partial }{\partial i}\left( {e_2 \,\sigma _1 A^{lT}\;\frac{\partial T}{\partial s}} \right)} \right|_s } \right. \\ 90 & \qquad \qquad \quad \left. {+\frac{e_2 \,\sigma _1 }{e_3}A^{lT}\;\frac{\partial T}{\partial s} \;\frac{\partial e_3 }{\partial i}} \right|_s -e_2 A^{lT}\;\frac{\partial \sigma _1 }{\partial s}\left. {\frac{\partial T}{\partial i}} \right|_s \\ 91 & \qquad \qquad \quad-e_2 \,\sigma _1 \frac{\partial}{\partial s}\left( {A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s } \right)+\frac{\partial }{\partial s}\left( {\frac{e_1 \,e_2 \,\sigma _1 ^2}{e_3 }A^{lT}\;\frac{\partial T}{\partial s}} \right) \\ 92 & \qquad \qquad \quad\shoveright{ \left. {-\frac{\partial \left( {e_1 \,e_2 \,\sigma _1 } \right)}{\partial s} \left( {\frac{\sigma _1 }{e_3}A^{lT}\;\frac{\partial T}{\partial s}} \right) + \frac{\partial }{\partial s}\left( {\frac{e_1 \,e_2 }{e_3 }A^{vT}\;\frac{\partial T}{\partial s}} \right)\;\;\;} \right]} \\ 93 % 94 \allowdisplaybreaks 89 &=\frac{1}{e_1 \,e_2 \,e_3 } \left[ {\left. {\;\;\;\frac{\partial }{\partial i} \left( {\frac{e_2 \,e_3 }{e_1 }A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s } \right)} \right|_s \left. {-\frac{\partial }{\partial i}\left( {e_2 \,\sigma _1 A^{lT}\;\frac{\partial T}{\partial s}} \right)} \right|_s } \right. \\ 90 & \qquad \qquad \quad \left. {+\frac{e_2 \,\sigma _1 }{e_3}A^{lT}\;\frac{\partial T}{\partial s} \;\frac{\partial e_3 }{\partial i}} \right|_s -e_2 A^{lT}\;\frac{\partial \sigma _1 }{\partial s}\left. {\frac{\partial T}{\partial i}} \right|_s \\ 91 & \qquad \qquad \quad-e_2 \,\sigma _1 \frac{\partial}{\partial s}\left( {A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s } \right)+\frac{\partial }{\partial s}\left( {\frac{e_1 \,e_2 \,\sigma _1 ^2}{e_3 }A^{lT}\;\frac{\partial T}{\partial s}} \right) \\ 92 & \qquad \qquad \quad\shoveright{ \left. {-\frac{\partial \left( {e_1 \,e_2 \,\sigma _1 } \right)}{\partial s} \left( {\frac{\sigma _1 }{e_3}A^{lT}\;\frac{\partial T}{\partial s}} \right) + \frac{\partial }{\partial s}\left( {\frac{e_1 \,e_2 }{e_3 }A^{vT}\;\frac{\partial T}{\partial s}} \right)\;\;\;} \right]} 93 \end{array} } \\ 94 {\begin{array}{*{20}l} 95 % 95 96 \intertext{using the same remark as just above, it becomes:} 96 97 % 97 &= \frac{1}{e_1 \,e_2 \,e_3 } \left[ {\left. {\;\;\;\frac{\partial }{\partial i} \left( {\frac{e_2 \,e_3 }{e_1 }A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s -e_2 \,\sigma _1 A^{lT}\;\frac{\partial T}{\partial s}} \right)} \right|_s } \right.\;\;\; \\ 98 & \qquad \qquad \quad+\frac{e_1 \,e_2 \,\sigma _1 }{e_3 }A^{lT}\;\frac{\partial T}{\partial s}\;\frac{\partial \sigma _1 }{\partial s} - \frac {\sigma _1 }{e_3} A^{lT} \;\frac{\partial \left( {e_1 \,e_2 \,\sigma _1 } \right)}{\partial s}\;\frac{\partial T}{\partial s} \\ 99 & \qquad \qquad \quad-e_2 \left( {A^{lT}\;\frac{\partial \sigma _1 }{\partial s}\left. {\frac{\partial T}{\partial i}} \right|_s +\frac{\partial }{\partial s}\left( {\sigma _1 A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s } \right)-\frac{\partial \sigma _1 }{\partial s}\;A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s } \right) \\ 100 & \qquad \qquad \quad\shoveright{\left. {+\frac{\partial }{\partial s}\left( {\frac{e_1 \,e_2 \,\sigma _1 ^2}{e_3 }A^{lT}\;\frac{\partial T}{\partial s}+\frac{e_1 \,e_2}{e_3 }A^{vT}\;\frac{\partial T}{\partial s}} \right)\;\;\;} \right] }\\ 101 % 102 \allowdisplaybreaks 103 \intertext{Since the horizontal scale factors do not depend on the vertical coordinate, 104 the last term of the first line and the first term of the last line cancel, while 98 &= \frac{1}{e_1 \,e_2 \,e_3 } \left[ {\left. {\;\;\;\frac{\partial }{\partial i} \left( {\frac{e_2 \,e_3 }{e_1 }A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s -e_2 \,\sigma _1 A^{lT}\;\frac{\partial T}{\partial s}} \right)} \right|_s } \right.\;\;\; \\ 99 & \qquad \qquad \quad+\frac{e_1 \,e_2 \,\sigma _1 }{e_3 }A^{lT}\;\frac{\partial T}{\partial s}\;\frac{\partial \sigma _1 }{\partial s} - \frac {\sigma _1 }{e_3} A^{lT} \;\frac{\partial \left( {e_1 \,e_2 \,\sigma _1 } \right)}{\partial s}\;\frac{\partial T}{\partial s} \\ 100 & \qquad \qquad \quad-e_2 \left( {A^{lT}\;\frac{\partial \sigma _1 }{\partial s}\left. {\frac{\partial T}{\partial i}} \right|_s +\frac{\partial }{\partial s}\left( {\sigma _1 A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s } \right)-\frac{\partial \sigma _1 }{\partial s}\;A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s } \right) \\ 101 & \qquad \qquad \quad\shoveright{\left. {+\frac{\partial }{\partial s}\left( {\frac{e_1 \,e_2 \,\sigma _1 ^2}{e_3 }A^{lT}\;\frac{\partial T}{\partial s}+\frac{e_1 \,e_2}{e_3 }A^{vT}\;\frac{\partial T}{\partial s}} \right)\;\;\;} \right] } 102 \end{array} } \\ 103 {\begin{array}{*{20}l} 104 % 105 \intertext{Since the horizontal scale factors do not depend on the vertical coordinate, 106 the last term of the first line and the first term of the last line cancel, while 105 107 the second line reduces to a single vertical derivative, so it becomes:} 106 108 % 107 & =\frac{1}{e_1 \,e_2 \,e_3 }\left[ {\left. {\;\;\;\frac{\partial }{\partial i}\left( {\frac{e_2 \,e_3 }{e_1 }A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s -e_2 \,\sigma _1 \,A^{lT}\;\frac{\partial T}{\partial s}} \right)} \right|_s } \right. \\ 108 & \qquad \qquad \quad \shoveright{ \left. {+\frac{\partial }{\partial s}\left( {-e_2 \,\sigma _1 \,A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s +A^{lT}\frac{e_1 \,e_2 }{e_3 }\;\left( {\varepsilon +\sigma _1 ^2} \right)\frac{\partial T}{\partial s}} \right)\;\;\;} \right]} \\109 % 110 \allowdisplaybreaks 111 \intertext{in other words, the horizontal Laplacian operator in the ($i$,$s$) plane takes the following form:}112 \end{array} } 113 % 114 D^T ={\frac{1}{e_1\,e_2\,e_3}}109 & =\frac{1}{e_1 \,e_2 \,e_3 }\left[ {\left. {\;\;\;\frac{\partial }{\partial i}\left( {\frac{e_2 \,e_3 }{e_1 }A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s -e_2 \,\sigma _1 \,A^{lT}\;\frac{\partial T}{\partial s}} \right)} \right|_s } \right. \\ 110 & \qquad \qquad \quad \shoveright{ \left. {+\frac{\partial }{\partial s}\left( {-e_2 \,\sigma _1 \,A^{lT}\;\left. {\frac{\partial T}{\partial i}} \right|_s +A^{lT}\frac{e_1 \,e_2 }{e_3 }\;\left( {\varepsilon +\sigma _1 ^2} \right)\frac{\partial T}{\partial s}} \right)\;\;\;} \right]} 111 \\ 112 % 113 \intertext{in other words, the horizontal/vertical Laplacian operator in the ($i$,$s$) plane takes the following form:} 114 \end{array} } \\ 115 % 116 {\frac{1}{e_1\,e_2\,e_3}} 115 117 \left( {{\begin{array}{*{30}c} 116 118 {\left. {\frac{\partial \left( {e_2 e_3 \bullet } \right)}{\partial i}} \right|_s } \hfill \\ … … 120 122 \left( {{\begin{array}{*{30}c} 121 123 {1} \hfill & {-\sigma_1 } \hfill \\ 122 {-\sigma_1} \hfill & {\varepsilon _1^2} \hfill \\123 \end{array} }} \right) 124 \cdot 124 {-\sigma_1} \hfill & {\varepsilon + \sigma_1^2} \hfill \\ 125 \end{array} }} \right) 126 \cdot 125 127 \left( {{\begin{array}{*{30}c} 126 128 {\frac{1}{e_1 }\;\left. {\frac{\partial \bullet }{\partial i}} \right|_s } \hfill \\ … … 129 131 \end{align*} 130 132 \end{subequations} 131 133 \addtocounter{equation}{-2} 132 134 133 135 % ================================================================ … … 137 139 \label{Apdx_B_2} 138 140 139 140 The iso/diapycnal diffusive tensor $\textbf {A}_{\textbf I}$ expressed in the ($i$,$j$,$k$) 141 curvilinear coordinate system in which the equations of the ocean circulation model are 141 \subsubsection*{In z-coordinates} 142 143 The iso/diapycnal diffusive tensor $\textbf {A}_{\textbf I}$ expressed in the ($i$,$j$,$k$) 144 curvilinear coordinate system in which the equations of the ocean circulation model are 142 145 formulated, takes the following form \citep{Redi_JPO82}: 143 146 144 \begin{equation *}147 \begin{equation} \label{Apdx_B3} 145 148 \textbf {A}_{\textbf I} = \frac{A^{lT}}{\left( {1+a_1 ^2+a_2 ^2} \right)} 146 149 \left[ {{\begin{array}{*{20}c} … … 149 152 {-a_1 } \hfill & {-a_2 } \hfill & {\varepsilon +a_1 ^2+a_2 ^2} \hfill \\ 150 153 \end{array} }} \right] 151 \end{equation*} 152 where ($a_1$, $a_2$) are the isopycnal slopes in ($\textbf{i}$, $\textbf{j}$) directions: 154 \end{equation} 155 where ($a_1$, $a_2$) are the isopycnal slopes in ($\textbf{i}$, 156 $\textbf{j}$) directions, relative to geopotentials: 153 157 \begin{equation*} 154 158 a_1 =\frac{e_3 }{e_1 }\left( {\frac{\partial \rho }{\partial i}} \right)\left( {\frac{\partial \rho }{\partial k}} \right)^{-1} 155 159 \qquad , \qquad 156 a_2 =\frac{e_3 }{e_2 }\left( {\frac{\partial \rho }{\partial j}} 160 a_2 =\frac{e_3 }{e_2 }\left( {\frac{\partial \rho }{\partial j}} 157 161 \right)\left( {\frac{\partial \rho }{\partial k}} \right)^{-1} 158 162 \end{equation*} 159 163 160 In practice, the isopycnal slopes are generally less than $10^{-2}$ in the ocean, so164 In practice, isopycnal slopes are generally less than $10^{-2}$ in the ocean, so 161 165 $\textbf {A}_{\textbf I}$ can be simplified appreciably \citep{Cox1987}: 162 \begin{equation*} 163 {\textbf{A}_{\textbf{I}}} \approx A^{lT} 166 \begin{subequations} \label{Apdx_B4} 167 \begin{equation} \label{Apdx_B4a} 168 {\textbf{A}_{\textbf{I}}} \approx A^{lT}\;\Re\;\text{where} \;\Re = 164 169 \left[ {{\begin{array}{*{20}c} 165 170 1 \hfill & 0 \hfill & {-a_1 } \hfill \\ 166 171 0 \hfill & 1 \hfill & {-a_2 } \hfill \\ 167 172 {-a_1 } \hfill & {-a_2 } \hfill & {\varepsilon +a_1 ^2+a_2 ^2} \hfill \\ 168 \end{array} }} \right] 169 \end{equation*} 170 171 The resulting isopycnal operator conserves the quantity and dissipates its square. 172 The demonstration of the first property is trivial as \eqref{Apdx_B2} is the divergence 173 \end{array} }} \right], 174 \end{equation} 175 and the iso/dianeutral diffusive operator in $z$-coordinates is then 176 \begin{equation}\label{Apdx_B4b} 177 D^T = \left. \nabla \right|_z \cdot 178 \left[ A^{lT} \;\Re \cdot \left. \nabla \right|_z T \right]. \\ 179 \end{equation} 180 \end{subequations} 181 182 183 Physically, the full tensor \eqref{Apdx_B3} 184 represents strong isoneutral diffusion on a plane parallel to the isoneutral 185 surface and weak dianeutral diffusion perpendicular to this plane. 186 However, the approximate `weak-slope' tensor \eqref{Apdx_B4a} represents strong 187 diffusion along the isoneutral surface, with weak 188 \emph{vertical} diffusion -- the principal axes of the tensor are no 189 longer orthogonal. This simplification also decouples 190 the ($i$,$z$) and ($j$,$z$) planes of the tensor. The weak-slope operator therefore takes the same 191 form, \eqref{Apdx_B4}, as \eqref{Apdx_B2}, the diffusion operator for geopotential 192 diffusion written in non-orthogonal $i,j,s$-coordinates. Written out 193 explicitly, 194 195 \begin{multline} \label{Apdx_B_ldfiso} 196 D^T=\frac{1}{e_1 e_2 }\left\{ 197 {\;\frac{\partial }{\partial i}\left[ {A_h \left( {\frac{e_2}{e_1}\frac{\partial T}{\partial i}-a_1 \frac{e_2}{e_3}\frac{\partial T}{\partial k}} \right)} \right]} 198 {+\frac{\partial}{\partial j}\left[ {A_h \left( {\frac{e_1}{e_2}\frac{\partial T}{\partial j}-a_2 \frac{e_1}{e_3}\frac{\partial T}{\partial k}} \right)} \right]\;} \right\} \\ 199 \shoveright{+\frac{1}{e_3 }\frac{\partial }{\partial k}\left[ {A_h \left( {-\frac{a_1 }{e_1 }\frac{\partial T}{\partial i}-\frac{a_2 }{e_2 }\frac{\partial T}{\partial j}+\frac{\left( {a_1 ^2+a_2 ^2+\varepsilon} \right)}{e_3 }\frac{\partial T}{\partial k}} \right)} \right]}. \\ 200 \end{multline} 201 202 203 The isopycnal diffusion operator \eqref{Apdx_B4}, 204 \eqref{Apdx_B_ldfiso} conserves tracer quantity and dissipates its 205 square. The demonstration of the first property is trivial as \eqref{Apdx_B4} is the divergence 173 206 of fluxes. Let us demonstrate the second one: 174 207 \begin{equation*} 175 \iiint\limits_D T\;\nabla .\left( {\textbf{A}}_{\textbf{I}} \nabla T \right)\,dv 176 = -\iiint\limits_D \nabla T\;.\left( {\textbf{A}}_{\textbf{I}} \nabla T \right)\,dv 208 \iiint\limits_D T\;\nabla .\left( {\textbf{A}}_{\textbf{I}} \nabla T \right)\,dv 209 = -\iiint\limits_D \nabla T\;.\left( {\textbf{A}}_{\textbf{I}} \nabla T \right)\,dv, 177 210 \end{equation*} 178 since179 \begin{subequations} 180 \begin{align*} {\begin{array}{*{20}l} 181 \nabla T\;.\left( {{\rm {\bf A}}_{\rm {\bf I}} \nabla T} 182 \right)&=A^{lT}\left[ {\left( {\frac{\partial T}{\partial i}} \right)^2-2a_1 183 \frac{\partial T}{\partial i}\frac{\partial T}{\partial k}+\left( 184 {\frac{\partial T}{\partial j}} \right)^2} \right. \\ 211 and since 212 \begin{subequations} 213 \begin{align*} {\begin{array}{*{20}l} 214 \nabla T\;.\left( {{\rm {\bf A}}_{\rm {\bf I}} \nabla T} 215 \right)&=A^{lT}\left[ {\left( {\frac{\partial T}{\partial i}} \right)^2-2a_1 216 \frac{\partial T}{\partial i}\frac{\partial T}{\partial k}+\left( 217 {\frac{\partial T}{\partial j}} \right)^2} \right. \\ 185 218 &\qquad \qquad \qquad 186 { \left. -\,{2a_2 \frac{\partial T}{\partial j}\frac{\partial T}{\partial k}+\left( {a_1 ^2+a_2 ^2} \right)\left( {\frac{\partial T}{\partial k}} \right)^2} \right]} \\ 187 &=A_h \left[ {\left( {\frac{\partial T}{\partial i}-a_1 \frac{\partial T}{\partial k}} \right)^2+\left( {\frac{\partial T}{\partial j}-a_2 \frac{\partial T}{\partial k}} \right)^2} \right] \\ 219 { \left. -\,{2a_2 \frac{\partial T}{\partial j}\frac{\partial T}{\partial k}+\left( {a_1 ^2+a_2 ^2+\varepsilon} \right)\left( {\frac{\partial T}{\partial k}} \right)^2} \right]} \\ 220 &=A_h \left[ {\left( {\frac{\partial T}{\partial i}-a_1 \frac{\partial 221 T}{\partial k}} \right)^2+\left( {\frac{\partial T}{\partial 222 j}-a_2 \frac{\partial T}{\partial k}} \right)^2} 223 +\varepsilon \left(\frac{\partial T}{\partial k}\right) ^2\right] \\ 188 224 & \geq 0 189 \end{array} } 225 \end{array} } 190 226 \end{align*} 191 227 \end{subequations} 192 the property becomes obvious. 193 194 The resulting diffusion operator in $z$-coordinate has the following form : 195 \begin{multline*} \label{Apdx_B_ldfiso} 196 D^T=\frac{1}{e_1 e_2 }\left\{ 197 {\;\frac{\partial }{\partial i}\left[ {A_h \left( {\frac{e_2}{e_1}\frac{\partial T}{\partial i}-a_1 \frac{e_2}{e_3}\frac{\partial T}{\partial k}} \right)} \right]} 198 {+\frac{\partial}{\partial j}\left[ {A_h \left( {\frac{e_1}{e_2}\frac{\partial T}{\partial j}-a_2 \frac{e_1}{e_3}\frac{\partial T}{\partial k}} \right)} \right]\;} \right\} \\ 199 \shoveright{+\frac{1}{e_3 }\frac{\partial }{\partial k}\left[ {A_h \left( {-\frac{a_1 }{e_1 }\frac{\partial T}{\partial i}-\frac{a_2 }{e_2 }\frac{\partial T}{\partial j}+\frac{\left( {a_1 ^2+a_2 ^2} \right)}{e_3 }\frac{\partial T}{\partial k}} \right)} \right]} \\ 200 \end{multline*} 201 202 It has to be emphasised that the simplification introduced, leads to a decoupling 203 between ($i$,$z$) and ($j$,$z$) planes. The operator has therefore the same 204 expression as \eqref{Apdx_B3}, the diffusion operator obtained for geopotential 205 diffusion in the $s$-coordinate. 228 \addtocounter{equation}{-1} 229 the property becomes obvious. 230 231 \subsubsection*{In generalized vertical coordinates} 232 233 Because the weak-slope operator \eqref{Apdx_B4}, \eqref{Apdx_B_ldfiso} is decoupled 234 in the ($i$,$z$) and ($j$,$z$) planes, it may be transformed into 235 generalized $s$-coordinates in the same way as \eqref{Apdx_B_1} was transformed into 236 \eqref{Apdx_B_2}. The resulting operator then takes the simple form 237 238 \begin{equation} \label{Apdx_B_ldfiso_s} 239 D^T = \left. \nabla \right|_s \cdot 240 \left[ A^{lT} \;\Re \cdot \left. \nabla \right|_s T \right] \\ 241 \;\;\text{where} \;\Re =\left( {{\begin{array}{*{20}c} 242 1 \hfill & 0 \hfill & {-r _1 } \hfill \\ 243 0 \hfill & 1 \hfill & {-r _2 } \hfill \\ 244 {-r _1 } \hfill & {-r _2 } \hfill & {\varepsilon +r _1 245 ^2+r _2 ^2} \hfill \\ 246 \end{array} }} \right), 247 \end{equation} 248 249 where ($r_1$, $r_2$) are the isopycnal slopes in ($\textbf{i}$, 250 $\textbf{j}$) directions, relative to $s$-coordinate surfaces: 251 \begin{equation*} 252 r_1 =\frac{e_3 }{e_1 }\left( {\frac{\partial \rho }{\partial i}} \right)\left( {\frac{\partial \rho }{\partial s}} \right)^{-1} 253 \qquad , \qquad 254 r_2 =\frac{e_3 }{e_2 }\left( {\frac{\partial \rho }{\partial j}} 255 \right)\left( {\frac{\partial \rho }{\partial s}} \right)^{-1}. 256 \end{equation*} 257 258 To prove \eqref{Apdx_B5} by direct re-expression of \eqref{Apdx_B_ldfiso} is 259 straightforward, but laborious. An easier way is first to note (by reversing the 260 derivation of \eqref{Apdx_B_2} from \eqref{Apdx_B_1} ) that the 261 weak-slope operator may be \emph{exactly} reexpressed in 262 non-orthogonal $i,j,\rho$-coordinates as 263 264 \begin{equation} \label{Apdx_B5} 265 D^T = \left. \nabla \right|_\rho \cdot 266 \left[ A^{lT} \;\Re \cdot \left. \nabla \right|_\rho T \right] \\ 267 \;\;\text{where} \;\Re =\left( {{\begin{array}{*{20}c} 268 1 \hfill & 0 \hfill &0 \hfill \\ 269 0 \hfill & 1 \hfill & 0 \hfill \\ 270 0 \hfill & 0 \hfill & \varepsilon \hfill \\ 271 \end{array} }} \right). 272 \end{equation} 273 Then direct transformation from $i,j,\rho$-coordinates to 274 $i,j,s$-coordinates gives \eqref{Apdx_B_ldfiso_s} immediately. 275 276 Note that the weak-slope approximation is only made in 277 transforming from the (rotated,orthogonal) isoneutral axes to the 278 non-orthogonal $i,j,\rho$-coordinates. The further transformation 279 into $i,j,s$-coordinates is exact, whatever the steepness of 280 the $s$-surfaces, in the same way as the transformation of 281 horizontal/vertical Laplacian diffusion in $z$-coordinates, 282 \eqref{Apdx_B_1} onto $s$-coordinates is exact, however steep the $s$-surfaces. 283 206 284 207 285 % ================================================================ … … 211 289 \label{Apdx_B_3} 212 290 213 The second order momentum diffusion operator (Laplacian) in the $z$-coordinate 214 is found by applying \eqref{Eq_PE_lap_vector}, the expression for the Laplacian 215 of a vector, to the horizontal velocity vector : 291 The second order momentum diffusion operator (Laplacian) in the $z$-coordinate 292 is found by applying \eqref{Eq_PE_lap_vector}, the expression for the Laplacian 293 of a vector, to the horizontal velocity vector : 216 294 \begin{align*} 217 \Delta {\textbf{U}}_h 295 \Delta {\textbf{U}}_h 218 296 &=\nabla \left( {\nabla \cdot {\textbf{U}}_h } \right)- 219 297 \nabla \times \left( {\nabla \times {\textbf{U}}_h } \right) \\ … … 224 302 {\frac{1}{e_3 }\frac{\partial \chi }{\partial k}} \hfill \\ 225 303 \end{array} }} \right)-\left( {{\begin{array}{*{20}c} 226 {\frac{1}{e_2 }\frac{\partial \zeta }{\partial j}-\frac{1}{e_3 227 }\frac{\partial }{\partial k}\left( {\frac{1}{e_3 }\frac{\partial 304 {\frac{1}{e_2 }\frac{\partial \zeta }{\partial j}-\frac{1}{e_3 305 }\frac{\partial }{\partial k}\left( {\frac{1}{e_3 }\frac{\partial 228 306 u}{\partial k}} \right)} \hfill \\ 229 {\frac{1}{e_3 }\frac{\partial }{\partial k}\left( {-\frac{1}{e_3 230 }\frac{\partial v}{\partial k}} \right)-\frac{1}{e_1 }\frac{\partial \zeta 307 {\frac{1}{e_3 }\frac{\partial }{\partial k}\left( {-\frac{1}{e_3 308 }\frac{\partial v}{\partial k}} \right)-\frac{1}{e_1 }\frac{\partial \zeta 231 309 }{\partial i}} \hfill \\ 232 {\frac{1}{e_1 e_2 }\left[ {\frac{\partial }{\partial i}\left( {\frac{e_2 233 }{e_3 }\frac{\partial u}{\partial k}} \right)-\frac{\partial }{\partial 234 j}\left( {-\frac{e_1 }{e_3 }\frac{\partial v}{\partial k}} \right)} \right]} 310 {\frac{1}{e_1 e_2 }\left[ {\frac{\partial }{\partial i}\left( {\frac{e_2 311 }{e_3 }\frac{\partial u}{\partial k}} \right)-\frac{\partial }{\partial 312 j}\left( {-\frac{e_1 }{e_3 }\frac{\partial v}{\partial k}} \right)} \right]} 235 313 \hfill \\ 236 314 \end{array} }} \right) … … 249 327 \end{array} }} \right) 250 328 \end{align*} 251 Using \eqref{Eq_PE_div}, the definition of the horizontal divergence, the third 329 Using \eqref{Eq_PE_div}, the definition of the horizontal divergence, the third 252 330 componant of the second vector is obviously zero and thus : 253 331 \begin{equation*} … … 255 333 \end{equation*} 256 334 257 Note that this operator ensures a full separation between the vorticity and horizontal 258 divergence fields (see Appendix~\ref{Apdx_C}). It is only equal to a Laplacian 335 Note that this operator ensures a full separation between the vorticity and horizontal 336 divergence fields (see Appendix~\ref{Apdx_C}). It is only equal to a Laplacian 259 337 applied to each component in Cartesian coordinates, not on the sphere. 260 338 261 The horizontal/vertical second order (Laplacian type) operator used to diffuse 339 The horizontal/vertical second order (Laplacian type) operator used to diffuse 262 340 horizontal momentum in the $z$-coordinate therefore takes the following form : 263 341 \begin{equation} \label{Apdx_B_Lap_U} 264 {\textbf{D}}^{\textbf{U}} = 342 {\textbf{D}}^{\textbf{U}} = 265 343 \nabla _h \left( {A^{lm}\;\chi } \right) 266 344 - \nabla _h \times \left( {A^{lm}\;\zeta \;{\textbf{k}}} \right) 267 345 + \frac{1}{e_3 }\frac{\partial }{\partial k}\left( {\frac{A^{vm}\;}{e_3 } 268 \frac{\partial {\rm {\bf U}}_h }{\partial k}} \right) \\ 346 \frac{\partial {\rm {\bf U}}_h }{\partial k}} \right) \\ 269 347 \end{equation} 270 348 that is, in expanded form: 271 349 \begin{align*} 272 D^{\textbf{U}}_u 350 D^{\textbf{U}}_u 273 351 & = \frac{1}{e_1} \frac{\partial \left( {A^{lm}\chi } \right)}{\partial i} 274 352 -\frac{1}{e_2} \frac{\partial \left( {A^{lm}\zeta } \right)}{\partial j} 275 353 +\frac{1}{e_3} \frac{\partial u}{\partial k} \\ 276 D^{\textbf{U}}_v 354 D^{\textbf{U}}_v 277 355 & = \frac{1}{e_2 }\frac{\partial \left( {A^{lm}\chi } \right)}{\partial j} 278 356 +\frac{1}{e_1 }\frac{\partial \left( {A^{lm}\zeta } \right)}{\partial i} … … 280 358 \end{align*} 281 359 282 Note Bene: introducing a rotation in \eqref{Apdx_B_Lap_U} does not lead to a 283 useful expression for the iso/diapycnal Laplacian operator in the $z$-coordinate. 284 Similarly, we did not found an expression of practical use for the geopotential 285 horizontal/vertical Laplacian operator in the $s$-coordinate. Generally, 286 \eqref{Apdx_B_Lap_U} is used in both $z$- and $s$-coordinate systems, that is 360 Note Bene: introducing a rotation in \eqref{Apdx_B_Lap_U} does not lead to a 361 useful expression for the iso/diapycnal Laplacian operator in the $z$-coordinate. 362 Similarly, we did not found an expression of practical use for the geopotential 363 horizontal/vertical Laplacian operator in the $s$-coordinate. Generally, 364 \eqref{Apdx_B_Lap_U} is used in both $z$- and $s$-coordinate systems, that is 287 365 a Laplacian diffusion is applied on momentum along the coordinate directions. -
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r2376 r3294 1 1 % ================================================================ 2 % Iso-neutral diffusion : 2 % Iso-neutral diffusion : 3 3 % ================================================================ 4 \chapter{Griffies's iso-neutral diffusion} 5 \label{Apdx_C} 4 \chapter[Iso-neutral diffusion and eddy advection using 5 triads]{Iso-neutral diffusion and eddy advection using triads} 6 \label{sec:triad} 6 7 \minitoc 7 8 \section{Griffies's formulation of iso-neutral diffusion} 9 10 \subsection{Introduction} 11 We define a scheme that get its inspiration from the scheme of 12 \citet{Griffies_al_JPO98}, but is formulated within the \NEMO 8 \pagebreak 9 \section{Choice of namelist parameters} 10 %-----------------------------------------nam_traldf------------------------------------------------------ 11 \namdisplay{namtra_ldf} 12 %--------------------------------------------------------------------------------------------------------- 13 If the namelist variable \np{ln\_traldf\_grif} is set true (and 14 \key{ldfslp} is set), \NEMO updates both active and passive tracers 15 using the Griffies triad representation of iso-neutral diffusion and 16 the eddy-induced advective skew (GM) fluxes. Otherwise (by default) the 17 filtered version of Cox's original scheme is employed 18 (\S\ref{LDF_slp}). In the present implementation of the Griffies 19 scheme, the advective skew fluxes are implemented even if 20 \key{traldf\_eiv} is not set. 21 22 Values of iso-neutral diffusivity and GM coefficient are set as 23 described in \S\ref{LDF_coef}. If none of the keys \key{traldf\_cNd}, 24 N=1,2,3 is set (the default), spatially constant iso-neutral $A_l$ and 25 GM diffusivity $A_e$ are directly set by \np{rn\_aeih\_0} and 26 \np{rn\_aeiv\_0}. If 2D-varying coefficients are set with 27 \key{traldf\_c2d} then $A_l$ is reduced in proportion with horizontal 28 scale factor according to \eqref{Eq_title} \footnote{Except in global 29 $0.5^{\circ}$ runs (\key{orca\_r05}) with \key{traldf\_eiv}, where 30 $A_l$ is set like $A_e$ but with a minimum vale of 31 $100\;\mathrm{m}^2\;\mathrm{s}^{-1}$}. In idealised setups with 32 \key{traldf\_c2d}, $A_e$ is reduced similarly, but if \key{traldf\_eiv} 33 is set in the global configurations \key{orca\_r2}, \key{orca\_r1} or 34 \key{orca\_r05} with \key{traldf\_c2d}, a horizontally varying $A_e$ is 35 instead set from the Held-Larichev parameterisation\footnote{In this 36 case, $A_e$ at low latitudes $|\theta|<20^{\circ}$ is further 37 reduced by a factor $|f/f_{20}|$, where $f_{20}$ is the value of $f$ 38 at $20^{\circ}$~N} (\mdl{ldfeiv}) and \np{rn\_aeiv\_0} is ignored 39 unless it is zero. 40 41 The options specific to the Griffies scheme include: 42 \begin{description}[font=\normalfont] 43 \item[\np{ln\_traldf\_gdia}] Default value is false. See \S\ref{sec:triad:sfdiag}. If this is set true, time-mean 44 eddy-advective (GM) velocities are output for diagnostic purposes, even 45 though the eddy advection is accomplished by means of the skew 46 fluxes. 47 \item[\np{ln\_traldf\_iso}] See \S\ref{sec:triad:taper}. If this is set false (the default), then 48 `iso-neutral' mixing is accomplished within the surface mixed-layer 49 along slopes linearly decreasing with depth from the value immediately below 50 the mixed-layer to zero (flat) at the surface (\S\ref{sec:triad:lintaper}). This is the same 51 treatment as used in the default implementation 52 \S\ref{LDF_slp_iso}; Fig.~\ref{Fig_eiv_slp}. Where 53 \np{ln\_traldf\_iso} is set true, the vertical skew flux is further 54 reduced to ensure no vertical buoyancy flux, giving an almost pure 55 horizontal diffusive tracer flux within the mixed layer. This is similar to 56 the tapering suggested by \citet{Gerdes1991}. See \S\ref{sec:triad:Gerdes-taper} 57 \item[\np{ln\_traldf\_botmix}] See \S\ref{sec:triad:iso_bdry}. If this 58 is set false (the default) then the lateral diffusive fluxes 59 associated with triads partly masked by topography are neglected. If 60 it is set true, however, then these lateral diffusive fluxes are 61 applied, giving smoother bottom tracer fields at the cost of 62 introducing diapycnal mixing. 63 \end{description} 64 \section{Triad formulation of iso-neutral diffusion} 65 \label{sec:triad:iso} 66 We have implemented into \NEMO a scheme inspired by \citet{Griffies_al_JPO98}, but formulated within the \NEMO 13 67 framework, using scale factors rather than grid-sizes. 14 68 15 The off-diagonal terms of the small angle diffusion tensor 16 \eqref{Eq_PE_iso_tensor} produce skew-fluxes along the 17 i- and j-directions resulting from the vertical tracer gradient: 18 \begin{align} 19 \label{eq:i13c} 20 &+\kappa r_1\frac{1}{e_3}\frac{\partial T}{\partial k},\qquad+\kappa r_2\frac{1}{e_3}\frac{\partial T}{\partial k}\\ 21 \intertext{and in the k-direction resulting from the lateral tracer gradients} 22 \label{eq:i31c} 23 & \kappa r_1\frac{1}{e_1}\frac{\partial T}{\partial i}+\kappa r_2\frac{1}{e_1}\frac{\partial T}{\partial i} 24 \end{align} 25 where \eqref{Eq_PE_iso_slopes} 69 \subsection{The iso-neutral diffusion operator} 70 The iso-neutral second order tracer diffusive operator for small 71 angles between iso-neutral surfaces and geopotentials is given by 72 \eqref{Eq_PE_iso_tensor}: 73 \begin{subequations} \label{eq:triad:PE_iso_tensor} 74 \begin{equation} 75 D^{lT}=-\Div\vect{f}^{lT}\equiv 76 -\frac{1}{e_1e_2e_3}\left[\pd{i}\left (f_1^{lT}e_2e_3\right) + 77 \pd{j}\left (f_2^{lT}e_2e_3\right) + \pd{k}\left (f_3^{lT}e_1e_2\right)\right], 78 \end{equation} 79 where the diffusive flux per unit area of physical space 80 \begin{equation} 81 \vect{f}^{lT}=-\Alt\Re\cdot\grad T, 82 \end{equation} 83 \begin{equation} 84 \label{eq:triad:PE_iso_tensor:c} 85 \mbox{with}\quad \;\;\Re = 86 \begin{pmatrix} 87 1&0&-r_1\mystrut \\ 88 0&1&-r_2\mystrut \\ 89 -r_1&-r_2&r_1 ^2+r_2 ^2\mystrut 90 \end{pmatrix} 91 \quad \text{and} \quad\grad T= 92 \begin{pmatrix} 93 \frac{1}{e_1}\pd[T]{i}\mystrut \\ 94 \frac{1}{e_2}\pd[T]{j}\mystrut \\ 95 \frac{1}{e_3}\pd[T]{k}\mystrut 96 \end{pmatrix}. 97 \end{equation} 98 \end{subequations} 99 % \left( {{\begin{array}{*{20}c} 100 % 1 \hfill & 0 \hfill & {-r_1 } \hfill \\ 101 % 0 \hfill & 1 \hfill & {-r_2 } \hfill \\ 102 % {-r_1 } \hfill & {-r_2 } \hfill & {r_1 ^2+r_2 ^2} \hfill \\ 103 % \end{array} }} \right) 104 Here \eqref{Eq_PE_iso_slopes} 26 105 \begin{align*} 27 106 r_1 &=-\frac{e_3 }{e_1 } \left( \frac{\partial \rho }{\partial i} … … 33 112 }{\partial k} \right)^{-1} 34 113 \end{align*} 35 is the i-component of the slope of the isoneutral surface relative to the computational 36 surface, and $r_2$ is the j-component. 37 38 The extra vertical diffusive flux associated with the $_{33}$ 114 is the $i$-component of the slope of the iso-neutral surface relative to the computational 115 surface, and $r_2$ is the $j$-component. 116 117 We will find it useful to consider the fluxes per unit area in $i,j,k$ 118 space; we write 119 \begin{equation} 120 \label{eq:triad:Fijk} 121 \vect{F}_{\mathrm{iso}}=\left(f_1^{lT}e_2e_3, f_2^{lT}e_1e_3, f_3^{lT}e_1e_2\right). 122 \end{equation} 123 Additionally, we will sometimes write the contributions towards the 124 fluxes $\vect{f}$ and $\vect{F}_\mathrm{iso}$ from the component 125 $R_{ij}$ of $\Re$ as $f_{ij}$, $F_{\mathrm{iso}\: ij}$, with 126 $f_{ij}=R_{ij}e_i^{-1}\partial T/\partial x_i$ (no summation) etc. 127 128 The off-diagonal terms of the small angle diffusion tensor 129 \eqref{Eq_PE_iso_tensor}, \eqref{eq:triad:PE_iso_tensor:c} produce skew-fluxes along the 130 $i$- and $j$-directions resulting from the vertical tracer gradient: 131 \begin{align} 132 \label{eq:triad:i13c} 133 f_{13}=&+\Alt r_1\frac{1}{e_3}\frac{\partial T}{\partial k},\qquad f_{23}=+\Alt r_2\frac{1}{e_3}\frac{\partial T}{\partial k}\\ 134 \intertext{and in the k-direction resulting from the lateral tracer gradients} 135 \label{eq:triad:i31c} 136 f_{31}+f_{32}=& \Alt r_1\frac{1}{e_1}\frac{\partial T}{\partial i}+\Alt r_2\frac{1}{e_1}\frac{\partial T}{\partial i} 137 \end{align} 138 139 The vertical diffusive flux associated with the $_{33}$ 39 140 component of the small angle diffusion tensor is 40 141 \begin{equation} 41 \label{eq: i33c}42 -\kappa(r_1^2 +r_2^2) \frac{1}{e_3}\frac{\partial T}{\partial k}.142 \label{eq:triad:i33c} 143 f_{33}=-\Alt(r_1^2 +r_2^2) \frac{1}{e_3}\frac{\partial T}{\partial k}. 43 144 \end{equation} 44 145 45 146 Since there are no cross terms involving $r_1$ and $r_2$ in the above, we can 46 consider the iso neutral diffusive fluxes separately in the i-k and j-k147 consider the iso-neutral diffusive fluxes separately in the $i$-$k$ and $j$-$k$ 47 148 planes, just adding together the vertical components from each 48 plane. The following description will describe the fluxes on the i-k149 plane. The following description will describe the fluxes on the $i$-$k$ 49 150 plane. 50 151 51 There is no natural discretization for the i-component of the52 skew-flux, \eqref{eq: i13c}, as53 although it must be evaluated at u-points, it involves vertical152 There is no natural discretization for the $i$-component of the 153 skew-flux, \eqref{eq:triad:i13c}, as 154 although it must be evaluated at $u$-points, it involves vertical 54 155 gradients (both for the tracer and the slope $r_1$), defined at 55 w-points. Similarly, the vertical skew flux, \eqref{eq:i31c}, is evaluated at56 w-points but involves horizontal gradients defined at u-points.156 $w$-points. Similarly, the vertical skew flux, \eqref{eq:triad:i31c}, is evaluated at 157 $w$-points but involves horizontal gradients defined at $u$-points. 57 158 58 159 \subsection{The standard discretization} 59 160 The straightforward approach to discretize the lateral skew flux 60 \eqref{eq: i13c} from tracer cell $i,k$ to $i+1,k$, introduced in 1995161 \eqref{eq:triad:i13c} from tracer cell $i,k$ to $i+1,k$, introduced in 1995 61 162 into OPA, \eqref{Eq_tra_ldf_iso}, is to calculate a mean vertical 62 gradient at the u-point from the average of the four surrounding163 gradient at the $u$-point from the average of the four surrounding 63 164 vertical tracer gradients, and multiply this by a mean slope at the 64 u-point, calculated from the averaged surrounding vertical density 65 gradients. The total area-integrated skew-flux from tracer cell $i,k$ 66 to $i+1,k$, noting that the $e_{{3u}_{i+1/2}^k}$ in the area 67 $e_{{3u}_{i+1/2}^k}e_{{2u}_{i+1/2}^k}$ at the u-point cancels out with 68 the $1/e_{{3u}_{i+1/2}^k}$ associated with the vertical tracer 165 $u$-point, calculated from the averaged surrounding vertical density 166 gradients. The total area-integrated skew-flux (flux per unit area in 167 $ijk$ space) from tracer cell $i,k$ 168 to $i+1,k$, noting that the $e_{{3}_{i+1/2}^k}$ in the area 169 $e{_{3}}_{i+1/2}^k{e_{2}}_{i+1/2}i^k$ at the $u$-point cancels out with 170 the $1/{e_{3}}_{i+1/2}^k$ associated with the vertical tracer 69 171 gradient, is then \eqref{Eq_tra_ldf_iso} 70 172 \begin{equation*} 71 \left(F_u^{ \mathrm{skew}} \right)_{i+\hhalf}^k = \kappa_{i+\hhalf}^k72 e_{{2u}_{i+1/2}^k}\overline{\overline173 \left(F_u^{13} \right)_{i+\hhalf}^k = \Alts_{i+\hhalf}^k 174 {e_{2}}_{i+1/2}^k \overline{\overline 73 175 r_1} ^{\,i,k}\,\overline{\overline{\delta_k T}}^{\,i,k}, 74 176 \end{equation*} … … 76 178 \begin{equation*} 77 179 \overline{\overline 78 r_1} ^{\,i,k} = -\frac{e_{{3u}_{i+1/2}^k}}{e_{{1u}_{i+1/2}^k}}79 \frac{\delta_{i+1/2} [\rho]}{\overline{\overline{\delta_k \rho}}^{\,i,k}} .180 r_1} ^{\,i,k} = -\frac{{e_{3u}}_{i+1/2}^k}{{e_{1u}}_{i+1/2}^k} 181 \frac{\delta_{i+1/2} [\rho]}{\overline{\overline{\delta_k \rho}}^{\,i,k}}, 80 182 \end{equation*} 81 183 and here and in the following we drop the $^{lT}$ superscript from 184 $\Alt$ for simplicity. 82 185 Unfortunately the resulting combination $\overline{\overline{\delta_k 83 186 \bullet}}^{\,i,k}$ of a $k$ average and a $k$ difference %of the tracer … … 89 192 global-average variance. To correct this, we introduced a smoothing of 90 193 the slopes of the iso-neutral surfaces (see \S\ref{LDF}). This 91 technique works f ine for $T$ and $S$as they are active tracers194 technique works for $T$ and $S$ in so far as they are active tracers 92 195 ($i.e.$ they enter the computation of density), but it does not work 93 196 for a passive tracer. … … 95 198 \citep{Griffies_al_JPO98} introduce a different discretization of the 96 199 off-diagonal terms that nicely solves the problem. 97 % Instead of multiplying the mean slope calculated at the u-point by98 % the mean vertical gradient at the u-point,200 % Instead of multiplying the mean slope calculated at the $u$-point by 201 % the mean vertical gradient at the $u$-point, 99 202 % >>>>>>>>>>>>>>>>>>>>>>>>>>>> 100 203 \begin{figure}[h] \begin{center} 101 204 \includegraphics[width=0.90\textwidth]{./TexFiles/Figures/Fig_triad_fluxes} 102 \caption{ \label{Fig_ISO_triad}205 \caption{ \label{fig:triad:ISO_triad} 103 206 (a) Arrangement of triads $S_i$ and tracer gradients to 104 give lateral tracer flux from box $i,k$ to $i+1,k$ 207 give lateral tracer flux from box $i,k$ to $i+1,k$ 105 208 (b) Triads $S'_i$ and tracer gradients to give vertical tracer flux from 106 209 box $i,k$ to $i,k+1$.} 107 \label{Fig_triad} 108 \end{center} \end{figure} 210 \end{center} \end{figure} 109 211 % >>>>>>>>>>>>>>>>>>>>>>>>>>>> 110 212 They get the skew flux from the products of the vertical gradients at 111 each w-point surrounding the u-point with the corresponding `triad'112 slope calculated from the lateral density gradient across the u-point113 divided by the vertical density gradient at the same w-point as the114 tracer gradient. See Fig.~\ref{ Fig_triad}a, where the thick lines213 each $w$-point surrounding the $u$-point with the corresponding `triad' 214 slope calculated from the lateral density gradient across the $u$-point 215 divided by the vertical density gradient at the same $w$-point as the 216 tracer gradient. See Fig.~\ref{fig:triad:ISO_triad}a, where the thick lines 115 217 denote the tracer gradients, and the thin lines the corresponding 116 218 triads, with slopes $s_1, \dotsc s_4$. The total area-integrated 117 219 skew-flux from tracer cell $i,k$ to $i+1,k$ 118 220 \begin{multline} 119 \label{eq: i13}120 \left( F_u^{13} \right)_{i+\frac{1}{2}}^k = \ kappa_{i+1}^k a_1 s_1221 \label{eq:triad:i13} 222 \left( F_u^{13} \right)_{i+\frac{1}{2}}^k = \Alts_{i+1}^k a_1 s_1 121 223 \delta _{k+\frac{1}{2}} \left[ T^{i+1} 122 \right]/e_{{3w}_{i+1}}^{k+\frac{1}{2}} + \ kappa_i^k a_2 s_2 \delta224 \right]/e_{{3w}_{i+1}}^{k+\frac{1}{2}} + \Alts _i^k a_2 s_2 \delta 123 225 _{k+\frac{1}{2}} \left[ T^i 124 226 \right]/e_{{3w}_{i+1}}^{k+\frac{1}{2}} \\ 125 +\ kappa_{i+1}^k a_3 s_3 \delta _{k-\frac{1}{2}} \left[ T^{i+1}126 \right]/e_{{3w}_{i+1}}^{k+\frac{1}{2}} +\ kappa_i^k a_4 s_4 \delta227 +\Alts _{i+1}^k a_3 s_3 \delta _{k-\frac{1}{2}} \left[ T^{i+1} 228 \right]/e_{{3w}_{i+1}}^{k+\frac{1}{2}} +\Alts _i^k a_4 s_4 \delta 127 229 _{k-\frac{1}{2}} \left[ T^i \right]/e_{{3w}_{i+1}}^{k+\frac{1}{2}}, 128 230 \end{multline} 129 231 where the contributions of the triad fluxes are weighted by areas 130 $a_1, \dotsc a_4$, and $\ kappa$ is now defined at the tracer points131 rather than the u-points. This discretization gives a much closer232 $a_1, \dotsc a_4$, and $\Alts$ is now defined at the tracer points 233 rather than the $u$-points. This discretization gives a much closer 132 234 stencil, and disallows the two-point computational modes. 133 235 134 The vertical skew flux \eqref{eq: i31c} from tracer cell $i,k$ to $i,k+1$ at the135 w-point $i,k+\hhalf$ is constructed similarly (Fig.~\ref{Fig_triad}b)236 The vertical skew flux \eqref{eq:triad:i31c} from tracer cell $i,k$ to $i,k+1$ at the 237 $w$-point $i,k+\hhalf$ is constructed similarly (Fig.~\ref{fig:triad:ISO_triad}b) 136 238 by multiplying lateral tracer gradients from each of the four 137 surrounding u-points by the appropriate triad slope:239 surrounding $u$-points by the appropriate triad slope: 138 240 \begin{multline} 139 \label{eq: i31}140 \left( F_w^{31} \right) _i ^{k+\frac{1}{2}} = \ kappa_i^{k+1} a_{1}'241 \label{eq:triad:i31} 242 \left( F_w^{31} \right) _i ^{k+\frac{1}{2}} = \Alts_i^{k+1} a_{1}' 141 243 s_{1}' \delta _{i-\frac{1}{2}} \left[ T^{k+1} \right]/{e_{3u}}_{i-\frac{1}{2}}^{k+1} 142 +\ kappa_i^{k+1} a_{2}' s_{2}' \delta _{i+\frac{1}{2}} \left[ T^{k+1} \right]/{e_{3u}}_{i+\frac{1}{2}}^{k+1}\\143 + \ kappa_i^k a_{3}' s_{3}' \delta _{i-\frac{1}{2}} \left[ T^k\right]/{e_{3u}}_{i-\frac{1}{2}}^k144 +\ kappa_i^k a_{4}' s_{4}' \delta _{i+\frac{1}{2}} \left[ T^k \right]/{e_{3u}}_{i+\frac{1}{2}}^k.244 +\Alts_i^{k+1} a_{2}' s_{2}' \delta _{i+\frac{1}{2}} \left[ T^{k+1} \right]/{e_{3u}}_{i+\frac{1}{2}}^{k+1}\\ 245 + \Alts_i^k a_{3}' s_{3}' \delta _{i-\frac{1}{2}} \left[ T^k\right]/{e_{3u}}_{i-\frac{1}{2}}^k 246 +\Alts_i^k a_{4}' s_{4}' \delta _{i+\frac{1}{2}} \left[ T^k \right]/{e_{3u}}_{i+\frac{1}{2}}^k. 145 247 \end{multline} 146 147 We notate the triad slopes in terms of the `anchor point' $i,k$148 (appearing in both the vertical and lateral gradient), and the u- and149 w-points $(i+i_p,k)$, $(i,k+k_p)$ at the centres of the `arms' of the150 triad as follows (see also Fig.~\ref{ Fig_triad}):151 \begin{equation} 152 \label{ Gf_slopes}153 _i^k \mathbb{R}_{i_p}^{k_p} 154 = \frac{ {e_{3w}}_{\,i}^{\,k+k_p}} { {e_{1u}}_{\,i+i_p}^{\,k}}248 249 We notate the triad slopes $s_i$ and $s'_i$ in terms of the `anchor point' $i,k$ 250 (appearing in both the vertical and lateral gradient), and the $u$- and 251 $w$-points $(i+i_p,k)$, $(i,k+k_p)$ at the centres of the `arms' of the 252 triad as follows (see also Fig.~\ref{fig:triad:ISO_triad}): 253 \begin{equation} 254 \label{eq:triad:R} 255 _i^k \mathbb{R}_{i_p}^{k_p} 256 =-\frac{ {e_{3w}}_{\,i}^{\,k+k_p}} { {e_{1u}}_{\,i+i_p}^{\,k}} 155 257 \ 156 \frac 258 \frac 157 259 {\left(\alpha / \beta \right)_i^k \ \delta_{i + i_p}[T^k] - \delta_{i + i_p}[S^k] } 158 260 {\left(\alpha / \beta \right)_i^k \ \delta_{k+k_p}[T^i ] - \delta_{k+k_p}[S^i ] }. … … 160 262 In calculating the slopes of the local neutral 161 263 surfaces, the expansion coefficients $\alpha$ and $\beta$ are 162 evaluated at the anchor points of the triad \footnote{Note that in \eqref{ Gf_slopes} we use the ratio $\alpha / \beta$264 evaluated at the anchor points of the triad \footnote{Note that in \eqref{eq:triad:R} we use the ratio $\alpha / \beta$ 163 265 instead of multiplying the temperature derivative by $\alpha$ and the 164 266 salinity derivative by $\beta$. This is more efficient as the ratio 165 267 $\alpha / \beta$ can to be evaluated directly}, while the metrics are 166 calculated at the u- and w-points on the arms.268 calculated at the $u$- and $w$-points on the arms. 167 269 168 270 % >>>>>>>>>>>>>>>>>>>>>>>>>>>> 169 271 \begin{figure}[h] \begin{center} 170 272 \includegraphics[width=0.60\textwidth]{./TexFiles/Figures/Fig_qcells} 171 \caption{ \label{Fig_ISO_triad_notation} 172 Triad notation for quarter cells.T-cells are inside 173 boxes, while the $i+\half,k$ u-cell is shaded in green and the 174 $i,k+\half$ w-cell is shaded in pink.} 175 \label{qcells} 273 \caption{ \label{fig:triad:qcells} 274 Triad notation for quarter cells.$T$-cells are inside 275 boxes, while the $i+\half,k$ $u$-cell is shaded in green and the 276 $i,k+\half$ $w$-cell is shaded in pink.} 176 277 \end{center} \end{figure} 177 278 % >>>>>>>>>>>>>>>>>>>>>>>>>>>> 178 279 179 Each triad $\{_i^k\:_{i_p}^{k_p}\}$ is associated (Fig.~\ref{ qcells}) with the quarter180 cell that is the intersection of the $i,k$ T-cell, the $i+i_p,k$181 u-cell and the $i,k+k_p$ w-cell. Expressing the slopes $s_i$ and182 $s'_i$ in \eqref{eq: i13} and \eqref{eq:i31} in this notation, we have280 Each triad $\{_i^k\:_{i_p}^{k_p}\}$ is associated (Fig.~\ref{fig:triad:qcells}) with the quarter 281 cell that is the intersection of the $i,k$ $T$-cell, the $i+i_p,k$ 282 $u$-cell and the $i,k+k_p$ $w$-cell. Expressing the slopes $s_i$ and 283 $s'_i$ in \eqref{eq:triad:i13} and \eqref{eq:triad:i31} in this notation, we have 183 284 e.g.\ $s_1=s'_1={\:}_i^k \mathbb{R}_{1/2}^{1/2}$. Each triad slope $_i^k 184 285 \mathbb{R}_{i_p}^{k_p}$ is used once (as an $s$) to calculate the 185 lateral flux along its u-arm, at $(i+i_p,k)$, and then again as an186 $s'$ to calculate the vertical flux along its w-arm at286 lateral flux along its $u$-arm, at $(i+i_p,k)$, and then again as an 287 $s'$ to calculate the vertical flux along its $w$-arm at 187 288 $(i,k+k_p)$. Each vertical area $a_i$ used to calculate the lateral 188 289 flux and horizontal area $a'_i$ used to calculate the vertical flux 189 can also be identified as the area across the u- and w-arms of a190 unique triad, and we cannotate these areas, similarly to the triad290 can also be identified as the area across the $u$- and $w$-arms of a 291 unique triad, and we notate these areas, similarly to the triad 191 292 slopes, as $_i^k{\mathbb{A}_u}_{i_p}^{k_p}$, 192 $_i^k{\mathbb{A}_w}_{i_p}^{k_p}$, where e.g. in \eqref{eq: i13}193 $a_{1}={\:}_i^k{\mathbb{A}_u}_{1/2}^{1/2}$, and in \eqref{eq: i31}293 $_i^k{\mathbb{A}_w}_{i_p}^{k_p}$, where e.g. in \eqref{eq:triad:i13} 294 $a_{1}={\:}_i^k{\mathbb{A}_u}_{1/2}^{1/2}$, and in \eqref{eq:triad:i31} 194 295 $a'_{1}={\:}_i^k{\mathbb{A}_w}_{1/2}^{1/2}$. 195 296 196 297 \subsection{The full triad fluxes} 197 A key property of iso neutral diffusion is that it should not affect298 A key property of iso-neutral diffusion is that it should not affect 198 299 the (locally referenced) density. In particular there should be no 199 300 lateral or vertical density flux. The lateral density flux disappears so long as the … … 202 303 form 203 304 \begin{equation} 204 \label{eq: i11}305 \label{eq:triad:i11} 205 306 \left( F_u^{11} \right) _{i+\frac{1}{2}} ^{k} = 206 - \left( \ kappa_i^{k+1} a_{1} + \kappa_i^{k+1} a_{2} + \kappa_i^k207 a_{3} + \ kappa_i^k a_{4} \right)307 - \left( \Alts_i^{k+1} a_{1} + \Alts_i^{k+1} a_{2} + \Alts_i^k 308 a_{3} + \Alts_i^k a_{4} \right) 208 309 \frac{\delta _{i+1/2} \left[ T^k\right]}{{e_{1u}}_{\,i+1/2}^{\,k}}, 209 310 \end{equation} 210 where the areas $a_i$ are as in \eqref{eq: i13}. In this case,211 separating the total lateral flux, the sum of \eqref{eq: i13} and212 \eqref{eq: i11}, into triad components, a lateral tracer311 where the areas $a_i$ are as in \eqref{eq:triad:i13}. In this case, 312 separating the total lateral flux, the sum of \eqref{eq:triad:i13} and 313 \eqref{eq:triad:i11}, into triad components, a lateral tracer 213 314 flux 214 315 \begin{equation} 215 \label{eq: latflux-triad}216 _i^k {\mathbb{F}_u}_{i_p}^{k_p} (T) = - A_i^k{ \:}_i^k{\mathbb{A}_u}_{i_p}^{k_p}316 \label{eq:triad:latflux-triad} 317 _i^k {\mathbb{F}_u}_{i_p}^{k_p} (T) = - \Alts_i^k{ \:}_i^k{\mathbb{A}_u}_{i_p}^{k_p} 217 318 \left( 218 319 \frac{ \delta_{i+ i_p}[T^k] }{ {e_{1u}}_{\,i + i_p}^{\,k} } … … 227 328 density flux associated with each triad separately disappears. 228 329 \begin{equation} 229 \label{eq: latflux-rho}330 \label{eq:triad:latflux-rho} 230 331 {\mathbb{F}_u}_{i_p}^{k_p} (\rho)=-\alpha _i^k {\:}_i^k {\mathbb{F}_u}_{i_p}^{k_p} (T) + \beta_i^k {\:}_i^k {\mathbb{F}_u}_{i_p}^{k_p} (S)=0 231 332 \end{equation} … … 234 335 to $i+1,k$ must also vanish since it is a sum of four such triad fluxes. 235 336 236 The squared slope $r_1^2$ in the expression \eqref{eq: i33c} for the337 The squared slope $r_1^2$ in the expression \eqref{eq:triad:i33c} for the 237 338 $_{33}$ component is also expressed in terms of area-weighted 238 339 squared triad slopes, so the area-integrated vertical flux from tracer 239 340 cell $i,k$ to $i,k+1$ resulting from the $r_1^2$ term is 240 341 \begin{equation} 241 \label{eq: i33}342 \label{eq:triad:i33} 242 343 \left( F_w^{33} \right) _i^{k+\frac{1}{2}} = 243 - \left( \ kappa_i^{k+1} a_{1}' s_{1}'^2244 + \ kappa_i^{k+1} a_{2}' s_{2}'^2245 + \ kappa_i^k a_{3}' s_{3}'^2246 + \ kappa_i^k a_{4}' s_{4}'^2 \right)\delta_{k+\frac{1}{2}} \left[ T^{i+1} \right],344 - \left( \Alts_i^{k+1} a_{1}' s_{1}'^2 345 + \Alts_i^{k+1} a_{2}' s_{2}'^2 346 + \Alts_i^k a_{3}' s_{3}'^2 347 + \Alts_i^k a_{4}' s_{4}'^2 \right)\delta_{k+\frac{1}{2}} \left[ T^{i+1} \right], 247 348 \end{equation} 248 349 where the areas $a'$ and slopes $s'$ are the same as in 249 \eqref{eq: i31}.250 Then, separating the total vertical flux, the sum of \eqref{eq: i31} and251 \eqref{eq: i33}, into triad components, a vertical flux350 \eqref{eq:triad:i31}. 351 Then, separating the total vertical flux, the sum of \eqref{eq:triad:i31} and 352 \eqref{eq:triad:i33}, into triad components, a vertical flux 252 353 \begin{align} 253 \label{eq: vertflux-triad}354 \label{eq:triad:vertflux-triad} 254 355 _i^k {\mathbb{F}_w}_{i_p}^{k_p} (T) 255 &= A_i^k{\: }_i^k{\mathbb{A}_w}_{i_p}^{k_p}356 &= \Alts_i^k{\: }_i^k{\mathbb{A}_w}_{i_p}^{k_p} 256 357 \left( 257 358 {_i^k\mathbb{R}_{i_p}^{k_p}}\frac{ \delta_{i+ i_p}[T^k] }{ {e_{1u}}_{\,i + i_p}^{\,k} } … … 260 361 \right) \\ 261 362 &= - \left(\left.{ }_i^k{\mathbb{A}_w}_{i_p}^{k_p}\right/{ }_i^k{\mathbb{A}_u}_{i_p}^{k_p}\right) 262 {_i^k\mathbb{R}_{i_p}^{k_p}}{\: }_i^k{\mathbb{F}_u}_{i_p}^{k_p} (T) \label{eq: vertflux-triad2}363 {_i^k\mathbb{R}_{i_p}^{k_p}}{\: }_i^k{\mathbb{F}_u}_{i_p}^{k_p} (T) \label{eq:triad:vertflux-triad2} 263 364 \end{align} 264 365 may be associated with each triad. Each vertical density flux $_i^k {\mathbb{F}_w}_{i_p}^{k_p} (\rho)$ … … 270 371 fluxes. 271 372 272 We can explicitly identify (Fig.~\ref{ qcells}) the triads associated with the $s_i$, $a_i$, and $s'_i$, $a'_i$ used in the definition of273 the u-fluxes and w-fluxes in274 \eqref{eq: i31}, \eqref{eq:i13}, \eqref{eq:i11} \eqref{eq:i33} and275 Fig.~\ref{ Fig_triad} to write out the iso-neutral fluxes at $u$- and373 We can explicitly identify (Fig.~\ref{fig:triad:qcells}) the triads associated with the $s_i$, $a_i$, and $s'_i$, $a'_i$ used in the definition of 374 the $u$-fluxes and $w$-fluxes in 375 \eqref{eq:triad:i31}, \eqref{eq:triad:i13}, \eqref{eq:triad:i11} \eqref{eq:triad:i33} and 376 Fig.~\ref{fig:triad:ISO_triad} to write out the iso-neutral fluxes at $u$- and 276 377 $w$-points as sums of the triad fluxes that cross the $u$- and $w$-faces: 277 378 %(Fig.~\ref{Fig_ISO_triad}): 278 \begin{flalign} \label{Eq_iso_flux} \ textbf{F}_{iso}(T) &\equiv379 \begin{flalign} \label{Eq_iso_flux} \vect{F}_\mathrm{iso}(T) &\equiv 279 380 \sum_{\substack{i_p,\,k_p}} 280 381 \begin{pmatrix} … … 284 385 \end{pmatrix}. 285 386 \end{flalign} 286 \subsection{Ensuring the scheme cannot increase tracer variance}287 \label{sec: variance}288 289 We now require that this operator cannot increase the387 \subsection{Ensuring the scheme does not increase tracer variance} 388 \label{sec:triad:variance} 389 390 We now require that this operator should not increase the 290 391 globally-integrated tracer variance. 291 392 %This changes according to 292 393 % \begin{align*} 293 394 % &\int_D D_l^T \; T \;dv \equiv \sum_{i,k} \left\{ T \ D_l^T \ b_T \right\} \\ 294 % &\equiv + \sum_{i,k} \sum_{\substack{i_p,\,k_p}} \left\{ 295 % \delta_{i} \left[{_{i+1/2-i_p}^k {\mathbb{F}_u }_{i_p}^{k_p}} \right] 395 % &\equiv + \sum_{i,k} \sum_{\substack{i_p,\,k_p}} \left\{ 396 % \delta_{i} \left[{_{i+1/2-i_p}^k {\mathbb{F}_u }_{i_p}^{k_p}} \right] 296 397 % + \delta_{k} \left[ {_i^{k+1/2-k_p} {\mathbb{F}_w}_{i_p}^{k_p}} \right] \ T \right\} \\ 297 % &\equiv - \sum_{i,k} \sum_{\substack{i_p,\,k_p}} \left\{ 398 % &\equiv - \sum_{i,k} \sum_{\substack{i_p,\,k_p}} \left\{ 298 399 % {_{i+1/2-i_p}^k {\mathbb{F}_u }_{i_p}^{k_p}} \ \delta_{i+1/2} [T] 299 400 % + {_i^{k+1/2-k_p} {\mathbb{F}_w}_{i_p}^{k_p}} \ \delta_{k+1/2} [T] \right\} \\ 300 401 % \end{align*} 301 402 Each triad slope $_i^k\mathbb{R}_{i_p}^{k_p}$ drives a lateral flux 302 $_i^k{\mathbb{F}_u}_{i_p}^{k_p} (T)$ across the u-point $i+i_p,k$ and403 $_i^k{\mathbb{F}_u}_{i_p}^{k_p} (T)$ across the $u$-point $i+i_p,k$ and 303 404 a vertical flux $_i^k{\mathbb{F}_w}_{i_p}^{k_p} (T)$ across the 304 w-point $i,k+k_p$. The lateral flux drives a net rate of change of305 variance at points $i+i_p-\half,k$ and $i+i_p+\half,k$of405 $w$-point $i,k+k_p$. The lateral flux drives a net rate of change of 406 variance, summed over the two $T$-points $i+i_p-\half,k$ and $i+i_p+\half,k$, of 306 407 \begin{multline} 307 408 {b_T}_{i+i_p-1/2}^k\left(\frac{\partial T}{\partial t}T\right)_{i+i_p-1/2}^k+ … … 311 412 &= -T_{i+i_p-1/2}^k{\;} _i^k{\mathbb{F}_u}_{i_p}^{k_p} (T) \quad + \quad T_{i+i_p+1/2}^k 312 413 {\;}_i^k{\mathbb{F}_u}_{i_p}^{k_p} (T) \\ 313 &={\;} _i^k{\mathbb{F}_u}_{i_p}^{k_p} (T)\,\delta_{i+ i_p}[T^k], \label{ locFdtdx}414 &={\;} _i^k{\mathbb{F}_u}_{i_p}^{k_p} (T)\,\delta_{i+ i_p}[T^k], \label{eq:triad:dvar_iso_i} 314 415 \end{split} 315 416 \end{multline} 316 while the vertical flux similarly drives a net rate of change of variance at points $i,k+k_p-\half$ and 317 $i,k+k_p+\half$ of 318 \begin{equation} 319 \label{locFdtdz} 417 while the vertical flux similarly drives a net rate of change of 418 variance summed over the $T$-points $i,k+k_p-\half$ (above) and 419 $i,k+k_p+\half$ (below) of 420 \begin{equation} 421 \label{eq:triad:dvar_iso_k} 320 422 _i^k{\mathbb{F}_w}_{i_p}^{k_p} (T) \,\delta_{k+ k_p}[T^i]. 321 423 \end{equation} 322 424 The total variance tendency driven by the triad is the sum of these 323 425 two. Expanding $_i^k{\mathbb{F}_u}_{i_p}^{k_p} (T)$ and 324 $_i^k{\mathbb{F}_w}_{i_p}^{k_p} (T)$ with \eqref{eq: latflux-triad} and325 \eqref{eq: vertflux-triad}, it is426 $_i^k{\mathbb{F}_w}_{i_p}^{k_p} (T)$ with \eqref{eq:triad:latflux-triad} and 427 \eqref{eq:triad:vertflux-triad}, it is 326 428 \begin{multline*} 327 - A_i^k\left \{429 -\Alts_i^k\left \{ 328 430 { } _i^k{\mathbb{A}_u}_{i_p}^{k_p} 329 431 \left( … … 343 445 to be related to a triad volume $_i^k\mathbb{V}_{i_p}^{k_p}$ by 344 446 \begin{equation} 345 \label{eq: V-A}447 \label{eq:triad:V-A} 346 448 _i^k\mathbb{V}_{i_p}^{k_p} 347 449 ={\;}_i^k{\mathbb{A}_u}_{i_p}^{k_p}\,{e_{1u}}_{\,i + i_p}^{\,k} … … 350 452 the variance tendency reduces to the perfect square 351 453 \begin{equation} 352 \label{eq: perfect-square}353 - A_i^k{\:} _i^k\mathbb{V}_{i_p}^{k_p}454 \label{eq:triad:perfect-square} 455 -\Alts_i^k{\:} _i^k\mathbb{V}_{i_p}^{k_p} 354 456 \left( 355 457 \frac{ \delta_{i+ i_p}[T^k] }{ {e_{1u}}_{\,i + i_p}^{\,k} } … … 358 460 \right)^2\leq 0. 359 461 \end{equation} 360 Thus, the constraint \eqref{eq: V-A} ensures that the fluxesassociated462 Thus, the constraint \eqref{eq:triad:V-A} ensures that the fluxes (\ref{eq:triad:latflux-triad}, \ref{eq:triad:vertflux-triad}) associated 361 463 with a given slope triad $_i^k\mathbb{R}_{i_p}^{k_p}$ do not increase 362 464 the net variance. Since the total fluxes are sums of such fluxes from … … 365 467 increase. 366 468 367 The expression \eqref{eq: V-A} can be interpreted as a discretization469 The expression \eqref{eq:triad:V-A} can be interpreted as a discretization 368 470 of the global integral 369 471 \begin{equation} 370 \label{eq: cts-var}371 \frac{\partial}{\partial t}\int\ half T^2\, dV =372 \int\ mathbf{F}\cdot\nabla T\, dV,472 \label{eq:triad:cts-var} 473 \frac{\partial}{\partial t}\int\!\half T^2\, dV = 474 \int\!\mathbf{F}\cdot\nabla T\, dV, 373 475 \end{equation} 374 476 where, within each triad volume $_i^k\mathbb{V}_{i_p}^{k_p}$, the … … 376 478 \[ 377 479 \mathbf{F}=\left( 378 _i^k{\mathbb{F}_u}_{i_p}^{k_p} (T)/_i^k{\mathbb{A}_u}_{i_p}^{k_p},379 {\:}_i^k{\mathbb{F}_w}_{i_p}^{k_p} (T)/_i^k{\mathbb{A}_w}_{i_p}^{k_p}480 \left.{}_i^k{\mathbb{F}_u}_{i_p}^{k_p} (T)\right/{}_i^k{\mathbb{A}_u}_{i_p}^{k_p}, 481 \left.{\:}_i^k{\mathbb{F}_w}_{i_p}^{k_p} (T)\right/{}_i^k{\mathbb{A}_w}_{i_p}^{k_p} 380 482 \right) 381 483 \] 382 484 and the gradient 383 485 \[\nabla T = \left( 384 \ delta_{i+ i_p}[T^k]/ {e_{1u}}_{\,i + i_p}^{\,k},385 \ delta_{k+ k_p}[T^i]/ {e_{3w}}_{\,i}^{\,k + k_p}486 \left.\delta_{i+ i_p}[T^k] \right/ {e_{1u}}_{\,i + i_p}^{\,k}, 487 \left.\delta_{k+ k_p}[T^i] \right/ {e_{3w}}_{\,i}^{\,k + k_p} 386 488 \right) 387 489 \] … … 390 492 volumes $_i^k\mathbb{V}_{i_p}^{k_p}$. \citet{Griffies_al_JPO98} identify 391 493 these $_i^k\mathbb{V}_{i_p}^{k_p}$ as the volumes of the quarter 392 cells, defined in terms of the distances between T, u,fand393 w-points. This is the natural discretization of394 \eqref{eq: cts-var}. The \NEMO model, however, operates with scale494 cells, defined in terms of the distances between $T$, $u$,$f$ and 495 $w$-points. This is the natural discretization of 496 \eqref{eq:triad:cts-var}. The \NEMO model, however, operates with scale 395 497 factors instead of grid sizes, and scale factors for the quarter 396 498 cells are not defined. Instead, therefore we simply choose 397 499 \begin{equation} 398 \label{eq: V-NEMO}500 \label{eq:triad:V-NEMO} 399 501 _i^k\mathbb{V}_{i_p}^{k_p}=\quarter {b_u}_{i+i_p}^k, 400 502 \end{equation} 401 as a quarter of the volume of the u-cell inside which the triad503 as a quarter of the volume of the $u$-cell inside which the triad 402 504 quarter-cell lies. This has the nice property that when the slopes 403 505 $\mathbb{R}$ vanish, the lateral flux from tracer cell $i,k$ to 404 506 $i+1,k$ reduces to the classical form 405 507 \begin{equation} 406 \label{eq: lat-normal}407 -\overline {A}_{\,i+1/2}^k\;508 \label{eq:triad:lat-normal} 509 -\overline\Alts_{\,i+1/2}^k\; 408 510 \frac{{b_u}_{i+1/2}^k}{{e_{1u}}_{\,i + i_p}^{\,k}} 409 511 \;\frac{\delta_{i+ 1/2}[T^k] }{{e_{1u}}_{\,i + i_p}^{\,k}} 410 = -\overline {A}_{\,i+1/2}^k\;\frac{{e_{1w}}_{\,i + 1/2}^{\,k}\:{e_{1v}}_{\,i + 1/2}^{\,k}}{{e_{1u}}_{\,i + 1/2}^{\,k}}.411 \end{equation} 412 In fact if the diffusive coefficient is defined at u-points, so that413 we employ $ A_{i+i_p}^k$ instead of $A_i^k$ in the definitions of the414 triad fluxes \eqref{eq: latflux-triad} and \eqref{eq:vertflux-triad},512 = -\overline\Alts_{\,i+1/2}^k\;\frac{{e_{1w}}_{\,i + 1/2}^{\,k}\:{e_{1v}}_{\,i + 1/2}^{\,k}\;\delta_{i+ 1/2}[T^k]}{{e_{1u}}_{\,i + 1/2}^{\,k}}. 513 \end{equation} 514 In fact if the diffusive coefficient is defined at $u$-points, so that 515 we employ $\Alts_{i+i_p}^k$ instead of $\Alts_i^k$ in the definitions of the 516 triad fluxes \eqref{eq:triad:latflux-triad} and \eqref{eq:triad:vertflux-triad}, 415 517 we can replace $\overline{A}_{\,i+1/2}^k$ by $A_{i+1/2}^k$ in the above. 416 518 417 519 \subsection{Summary of the scheme} 418 The divergence of the expression \eqref{Eq_iso_flux} for the fluxes gives the iso-neutral diffusion tendency at 520 The iso-neutral fluxes at $u$- and 521 $w$-points are the sums of the triad fluxes that cross the $u$- and 522 $w$-faces \eqref{Eq_iso_flux}: 523 \begin{subequations}\label{eq:triad:alltriadflux} 524 \begin{flalign}\label{eq:triad:vect_isoflux} 525 \vect{F}_\mathrm{iso}(T) &\equiv 526 \sum_{\substack{i_p,\,k_p}} 527 \begin{pmatrix} 528 {_{i+1/2-i_p}^k {\mathbb{F}_u}_{i_p}^{k_p} } (T) \\ 529 \\ 530 {_i^{k+1/2-k_p} {\mathbb{F}_w}_{i_p}^{k_p} } (T) 531 \end{pmatrix}, 532 \end{flalign} 533 where \eqref{eq:triad:latflux-triad}: 534 \begin{align} 535 \label{eq:triad:triadfluxu} 536 _i^k {\mathbb{F}_u}_{i_p}^{k_p} (T) &= - \Alts_i^k{ 537 \:}\frac{{{}_i^k\mathbb{V}}_{i_p}^{k_p}}{{e_{1u}}_{\,i + i_p}^{\,k}} 538 \left( 539 \frac{ \delta_{i+ i_p}[T^k] }{ {e_{1u}}_{\,i + i_p}^{\,k} } 540 -\ {_i^k\mathbb{R}_{i_p}^{k_p}} \ 541 \frac{ \delta_{k+k_p} [T^i] }{{e_{3w}}_{\,i}^{\,k+k_p} } 542 \right),\\ 543 \intertext{and} 544 _i^k {\mathbb{F}_w}_{i_p}^{k_p} (T) 545 &= \Alts_i^k{\: }\frac{{{}_i^k\mathbb{V}}_{i_p}^{k_p}}{{e_{3w}}_{\,i}^{\,k+k_p}} 546 \left( 547 {_i^k\mathbb{R}_{i_p}^{k_p}}\frac{ \delta_{i+ i_p}[T^k] }{ {e_{1u}}_{\,i + i_p}^{\,k} } 548 -\ \left({_i^k\mathbb{R}_{i_p}^{k_p}}\right)^2 \ 549 \frac{ \delta_{k+k_p} [T^i] }{{e_{3w}}_{\,i}^{\,k+k_p} } 550 \right),\label{eq:triad:triadfluxw} 551 \end{align} 552 with \eqref{eq:triad:V-NEMO} 553 \begin{equation} 554 \label{eq:triad:V-NEMO2} 555 _i^k{\mathbb{V}}_{i_p}^{k_p}=\quarter {b_u}_{i+i_p}^k. 556 \end{equation} 557 \end{subequations} 558 559 The divergence of the expression \eqref{Eq_iso_flux} for the fluxes gives the iso-neutral diffusion tendency at 419 560 each tracer point: 420 \begin{equation} \label{ Gf_operator} D_l^T = \frac{1}{b_T}561 \begin{equation} \label{eq:triad:iso_operator} D_l^T = \frac{1}{b_T} 421 562 \sum_{\substack{i_p,\,k_p}} \left\{ \delta_{i} \left[{_{i+1/2-i_p}^k 422 563 {\mathbb{F}_u }_{i_p}^{k_p}} \right] + \delta_{k} \left[ … … 427 568 \begin{description} 428 569 \item[$\bullet$ horizontal diffusion] The discretization of the 429 diffusion operator recovers \eqref{eq: lat-normal} the traditional five-point Laplacian in570 diffusion operator recovers \eqref{eq:triad:lat-normal} the traditional five-point Laplacian in 430 571 the limit of flat iso-neutral direction : 431 \begin{equation} \label{ Gf_property1a} D_l^T = \frac{1}{b_T} \572 \begin{equation} \label{eq:triad:iso_property0} D_l^T = \frac{1}{b_T} \ 432 573 \delta_{i} \left[ \frac{e_{2u}\,e_{3u}}{e_{1u}} \; 433 \overline {A}^{\,i} \; \delta_{i+1/2}[T] \right] \qquad574 \overline\Alts^{\,i} \; \delta_{i+1/2}[T] \right] \qquad 434 575 \text{when} \quad { _i^k \mathbb{R}_{i_p}^{k_p} }=0 435 576 \end{equation} … … 437 578 \item[$\bullet$ implicit treatment in the vertical] Only tracer values 438 579 associated with a single water column appear in the expression 439 \eqref{eq: i33} for the $_{33}$ fluxes, vertical fluxes driven by580 \eqref{eq:triad:i33} for the $_{33}$ fluxes, vertical fluxes driven by 440 581 vertical gradients. This is of paramount importance since it means 441 that an implicit in time algorithm can be used to solve the vertical 442 diffusion equation. This is a necessity since the vertical eddy 582 that a time-implicit algorithm can be used to solve the vertical 583 diffusion equation. This is necessary 584 since the vertical eddy 443 585 diffusivity associated with this term, 444 586 \begin{equation} 445 \frac{1}{b_w}\sum_{\substack{i_p, \,k_p}} \left\{ 446 {\:}_i^k\mathbb{V}_{i_p}^{k_p} \: A_i^k \: \left(_i^k \mathbb{R}_{i_p}^{k_p}\right)^2447 \right\} = 448 \frac{1}{4b_w}\sum_{\substack{i_p, \,k_p}} \left\{ 449 {b_u}_{i+i_p}^k\: A_i^k \: \left(_i^k \mathbb{R}_{i_p}^{k_p}\right)^2587 \frac{1}{b_w}\sum_{\substack{i_p, \,k_p}} \left\{ 588 {\:}_i^k\mathbb{V}_{i_p}^{k_p} \: \Alts_i^k \: \left(_i^k \mathbb{R}_{i_p}^{k_p}\right)^2 589 \right\} = 590 \frac{1}{4b_w}\sum_{\substack{i_p, \,k_p}} \left\{ 591 {b_u}_{i+i_p}^k\: \Alts_i^k \: \left(_i^k \mathbb{R}_{i_p}^{k_p}\right)^2 450 592 \right\}, 451 593 \end{equation} … … 454 596 \item[$\bullet$ pure iso-neutral operator] The iso-neutral flux of 455 597 locally referenced potential density is zero. See 456 \eqref{eq: latflux-rho} and \eqref{eq:vertflux-triad2}.598 \eqref{eq:triad:latflux-rho} and \eqref{eq:triad:vertflux-triad2}. 457 599 458 600 \item[$\bullet$ conservation of tracer] The iso-neutral diffusion 459 601 conserves tracer content, $i.e.$ 460 \begin{equation} \label{ Gf_property1} \sum_{i,j,k} \left\{ D_l^T \602 \begin{equation} \label{eq:triad:iso_property1} \sum_{i,j,k} \left\{ D_l^T \ 461 603 b_T \right\} = 0 462 604 \end{equation} … … 466 608 \item[$\bullet$ no increase of tracer variance] The iso-neutral diffusion 467 609 does not increase the tracer variance, $i.e.$ 468 \begin{equation} \label{ Gf_property1} \sum_{i,j,k} \left\{ T \ D_l^T610 \begin{equation} \label{eq:triad:iso_property2} \sum_{i,j,k} \left\{ T \ D_l^T 469 611 \ b_T \right\} \leq 0 470 612 \end{equation} 471 613 The property is demonstrated in 472 \ ref{sec:variance} above. It is a key property for a diffusion473 term. It means that it is also a dissipation term, $i.e.$ it is a474 di ffusion ofthe square of the quantity on which it is applied. It614 \S\ref{sec:triad:variance} above. It is a key property for a diffusion 615 term. It means that it is also a dissipation term, $i.e.$ it 616 dissipates the square of the quantity on which it is applied. It 475 617 therefore ensures that, when the diffusivity coefficient is large 476 enough, the field on which it is applied become free of grid-point618 enough, the field on which it is applied becomes free of grid-point 477 619 noise. 478 620 479 621 \item[$\bullet$ self-adjoint operator] The iso-neutral diffusion 480 622 operator is self-adjoint, $i.e.$ 481 \begin{equation} \label{ Gf_property1} \sum_{i,j,k} \left\{ S \ D_l^T623 \begin{equation} \label{eq:triad:iso_property3} \sum_{i,j,k} \left\{ S \ D_l^T 482 624 \ b_T \right\} = \sum_{i,j,k} \left\{ D_l^S \ T \ b_T \right\} 483 625 \end{equation} … … 486 628 routine. This property can be demonstrated similarly to the proof of 487 629 the `no increase of tracer variance' property. The contribution by a 488 single triad towards the left hand side of \eqref{ Gf_property1}, can489 be found by replacing $\delta[T]$ by $\delta[S]$ in \eqref{ locFdtdx}490 and \eqref{ locFdtdx}. This results in a term similar to491 \eqref{eq: perfect-square},492 \begin{equation} 493 \label{eq: TScovar}494 - A_i^k{\:} _i^k\mathbb{V}_{i_p}^{k_p}630 single triad towards the left hand side of \eqref{eq:triad:iso_property3}, can 631 be found by replacing $\delta[T]$ by $\delta[S]$ in \eqref{eq:triad:dvar_iso_i} 632 and \eqref{eq:triad:dvar_iso_k}. This results in a term similar to 633 \eqref{eq:triad:perfect-square}, 634 \begin{equation} 635 \label{eq:triad:TScovar} 636 - \Alts_i^k{\:} _i^k\mathbb{V}_{i_p}^{k_p} 495 637 \left( 496 638 \frac{ \delta_{i+ i_p}[T^k] }{ {e_{1u}}_{\,i + i_p}^{\,k} } … … 506 648 This is symmetrical in $T $ and $S$, so exactly the same term arises 507 649 from the discretization of this triad's contribution towards the 508 RHS of \eqref{ Gf_property1}.650 RHS of \eqref{eq:triad:iso_property3}. 509 651 \end{description} 510 511 512 $\ $\newline %force an empty line 652 \subsection{Treatment of the triads at the boundaries}\label{sec:triad:iso_bdry} 653 The triad slope can only be defined where both the grid boxes centred at 654 the end of the arms exist. Triads that would poke up 655 through the upper ocean surface into the atmosphere, or down into the 656 ocean floor, must be masked out. See Fig.~\ref{fig:triad:bdry_triads}. Surface layer triads 657 $\triad{i}{1}{R}{1/2}{-1/2}$ (magenta) and 658 $\triad{i+1}{1}{R}{-1/2}{-1/2}$ (blue) that require density to be 659 specified above the ocean surface are masked (Fig.~\ref{fig:triad:bdry_triads}a): this ensures that lateral 660 tracer gradients produce no flux through the ocean surface. However, 661 to prevent surface noise, it is customary to retain the $_{11}$ contributions towards 662 the lateral triad fluxes $\triad[u]{i}{1}{F}{1/2}{-1/2}$ and 663 $\triad[u]{i+1}{1}{F}{-1/2}{-1/2}$; this drives diapycnal tracer 664 fluxes. Similar comments apply to triads that would intersect the 665 ocean floor (Fig.~\ref{fig:triad:bdry_triads}b). Note that both near bottom 666 triad slopes $\triad{i}{k}{R}{1/2}{1/2}$ and 667 $\triad{i+1}{k}{R}{-1/2}{1/2}$ are masked when either of the $i,k+1$ 668 or $i+1,k+1$ tracer points is masked, i.e.\ the $i,k+1$ $u$-point is 669 masked. The associated lateral fluxes (grey-black dashed line) are 670 masked if \np{ln\_botmix\_grif}=false, but left unmasked, 671 giving bottom mixing, if \np{ln\_botmix\_grif}=true. 672 673 The default option \np{ln\_botmix\_grif}=false is suitable when the 674 bbl mixing option is enabled (\key{trabbl}, with \np{nn\_bbl\_ldf}=1), 675 or for simple idealized problems. For setups with topography without 676 bbl mixing, \np{ln\_botmix\_grif}=true may be necessary. 677 % >>>>>>>>>>>>>>>>>>>>>>>>>>>> 678 \begin{figure}[h] \begin{center} 679 \includegraphics[width=0.60\textwidth]{./TexFiles/Figures/Fig_bdry_triads} 680 \caption{ \label{fig:triad:bdry_triads} 681 (a) Uppermost model layer $k=1$ with $i,1$ and $i+1,1$ tracer 682 points (black dots), and $i+1/2,1$ $u$-point (blue square). Triad 683 slopes $\triad{i}{1}{R}{1/2}{-1/2}$ (magenta) and $\triad{i+1}{1}{R}{-1/2}{-1/2}$ 684 (blue) poking through the ocean surface are masked (faded in 685 figure). However, the lateral $_{11}$ contributions towards 686 $\triad[u]{i}{1}{F}{1/2}{-1/2}$ and $\triad[u]{i+1}{1}{F}{-1/2}{-1/2}$ 687 (yellow line) are still applied, giving diapycnal diffusive 688 fluxes.\\ 689 (b) Both near bottom triad slopes $\triad{i}{k}{R}{1/2}{1/2}$ and 690 $\triad{i+1}{k}{R}{-1/2}{1/2}$ are masked when either of the $i,k+1$ 691 or $i+1,k+1$ tracer points is masked, i.e.\ the $i,k+1$ $u$-point 692 is masked. The associated lateral fluxes (grey-black dashed 693 line) are masked if \np{botmix\_grif}=.false., but left 694 unmasked, giving bottom mixing, if \np{botmix\_grif}=.true.} 695 \end{center} \end{figure} 696 % >>>>>>>>>>>>>>>>>>>>>>>>>>>> 697 \subsection{ Limiting of the slopes within the interior}\label{sec:triad:limit} 698 As discussed in \S\ref{LDF_slp_iso}, iso-neutral slopes relative to 699 geopotentials must be bounded everywhere, both for consistency with the small-slope 700 approximation and for numerical stability \citep{Cox1987, 701 Griffies_Bk04}. The bound chosen in \NEMO is applied to each 702 component of the slope separately and has a value of $1/100$ in the ocean interior. 703 %, ramping linearly down above 70~m depth to zero at the surface 704 It is of course relevant to the iso-neutral slopes $\tilde{r}_i=r_i+\sigma_i$ relative to 705 geopotentials (here the $\sigma_i$ are the slopes of the coordinate surfaces relative to 706 geopotentials) \eqref{Eq_PE_slopes_eiv} rather than the slope $r_i$ relative to coordinate 707 surfaces, so we require 708 \begin{equation*} 709 |\tilde{r}_i|\leq \tilde{r}_\mathrm{max}=0.01. 710 \end{equation*} 711 and then recalculate the slopes $r_i$ relative to coordinates. 712 Each individual triad slope 713 \begin{equation} 714 \label{eq:triad:Rtilde} 715 _i^k\tilde{\mathbb{R}}_{i_p}^{k_p} = {}_i^k\mathbb{R}_{i_p}^{k_p} + \frac{\delta_{i+i_p}[z_T^k]}{{e_{1u}}_{\,i + i_p}^{\,k}} 716 \end{equation} 717 is limited like this and then the corresponding 718 $_i^k\mathbb{R}_{i_p}^{k_p} $ are recalculated and combined to form the fluxes. 719 Note that where the slopes have been limited, there is now a non-zero 720 iso-neutral density flux that drives dianeutral mixing. In particular this iso-neutral density flux 721 is always downwards, and so acts to reduce gravitational potential energy. 722 \subsection{Tapering within the surface mixed layer}\label{sec:triad:taper} 723 724 Additional tapering of the iso-neutral fluxes is necessary within the 725 surface mixed layer. When the Griffies triads are used, we offer two 726 options for this. 727 \subsubsection{Linear slope tapering within the surface mixed layer}\label{sec:triad:lintaper} 728 This is the option activated by the default choice 729 \np{ln\_triad\_iso}=false. Slopes $\tilde{r}_i$ relative to 730 geopotentials are tapered linearly from their value immediately below the mixed layer to zero at the 731 surface, as described in option (c) of Fig.~\ref{Fig_eiv_slp}, to values 732 \begin{subequations} 733 \begin{equation} 734 \label{eq:triad:rmtilde} 735 \rMLt = 736 -\frac{z}{h}\left.\tilde{r}_i\right|_{z=-h}\quad \text{ for } z>-h, 737 \end{equation} 738 and then the $r_i$ relative to vertical coordinate surfaces are appropriately 739 adjusted to 740 \begin{equation} 741 \label{eq:triad:rm} 742 \rML =\rMLt -\sigma_i \quad \text{ for } z>-h. 743 \end{equation} 744 \end{subequations} 745 Thus the diffusion operator within the mixed layer is given by: 746 \begin{equation} \label{eq:triad:iso_tensor_ML} 747 D^{lT}=\nabla {\rm {\bf .}}\left( {A^{lT}\;\Re \;\nabla T} \right) \qquad 748 \mbox{with}\quad \;\;\Re =\left( {{\begin{array}{*{20}c} 749 1 \hfill & 0 \hfill & {-\rML[1]}\hfill \\ 750 0 \hfill & 1 \hfill & {-\rML[2]} \hfill \\ 751 {-\rML[1]}\hfill & {-\rML[2]} \hfill & {\rML[1]^2+\rML[2]^2} \hfill 752 \end{array} }} \right) 753 \end{equation} 754 755 This slope tapering gives a natural connection between tracer in the 756 mixed-layer and in isopycnal layers immediately below, in the 757 thermocline. It is consistent with the way the $\tilde{r}_i$ are 758 tapered within the mixed layer (see \S\ref{sec:triad:taperskew} below) 759 so as to ensure a uniform GM eddy-induced velocity throughout the 760 mixed layer. However, it gives a downwards density flux and so acts so 761 as to reduce potential energy in the same way as does the slope 762 limiting discussed above in \S\ref{sec:triad:limit}. 763 764 As in \S\ref{sec:triad:limit} above, the tapering 765 \eqref{eq:triad:rmtilde} is applied separately to each triad 766 $_i^k\tilde{\mathbb{R}}_{i_p}^{k_p}$, and the 767 $_i^k\mathbb{R}_{i_p}^{k_p}$ adjusted. For clarity, we assume 768 $z$-coordinates in the following; the conversion from 769 $\mathbb{R}$ to $\tilde{\mathbb{R}}$ and back to $\mathbb{R}$ follows exactly as described 770 above by \eqref{eq:triad:Rtilde}. 771 \begin{enumerate} 772 \item Mixed-layer depth is defined so as to avoid including regions of weak 773 vertical stratification in the slope definition. 774 At each $i,j$ (simplified to $i$ in 775 Fig.~\ref{fig:triad:MLB_triad}), we define the mixed-layer by setting 776 the vertical index of the tracer point immediately below the mixed 777 layer, $k_\mathrm{ML}$, as the maximum $k$ (shallowest tracer point) 778 such that the potential density 779 ${\rho_0}_{i,k}>{\rho_0}_{i,k_{10}}+\Delta\rho_c$, where $i,k_{10}$ is 780 the tracer gridbox within which the depth reaches 10~m. See the left 781 side of Fig.~\ref{fig:triad:MLB_triad}. We use the $k_{10}$-gridbox 782 instead of the surface gridbox to avoid problems e.g.\ with thin 783 daytime mixed-layers. Currently we use the same 784 $\Delta\rho_c=0.01\;\mathrm{kg\:m^{-3}}$ for ML triad tapering as is 785 used to output the diagnosed mixed-layer depth 786 $h_\mathrm{ML}=|z_{W}|_{k_\mathrm{ML}+1/2}$, the depth of the $w$-point 787 above the $i,k_\mathrm{ML}$ tracer point. 788 789 \item We define `basal' triad slopes 790 ${\:}_i{\mathbb{R}_\mathrm{base}}_{\,i_p}^{k_p}$ as the slopes 791 of those triads whose vertical `arms' go down from the 792 $i,k_\mathrm{ML}$ tracer point to the $i,k_\mathrm{ML}-1$ tracer point 793 below. This is to ensure that the vertical density gradients 794 associated with these basal triad slopes 795 ${\:}_i{\mathbb{R}_\mathrm{base}}_{\,i_p}^{k_p}$ are 796 representative of the thermocline. The four basal triads defined in the bottom part 797 of Fig.~\ref{fig:triad:MLB_triad} are then 798 \begin{align} 799 {\:}_i{\mathbb{R}_\mathrm{base}}_{\,i_p}^{k_p} &= 800 {\:}^{k_\mathrm{ML}-k_p-1/2}_i{\mathbb{R}_\mathrm{base}}_{\,i_p}^{k_p}, \label{eq:triad:Rbase} 801 \\ 802 \intertext{with e.g.\ the green triad} 803 {\:}_i{\mathbb{R}_\mathrm{base}}_{1/2}^{-1/2}&= 804 {\:}^{k_\mathrm{ML}}_i{\mathbb{R}_\mathrm{base}}_{\,1/2}^{-1/2}. \notag 805 \end{align} 806 The vertical flux associated with each of these triads passes through the $w$-point 807 $i,k_\mathrm{ML}-1/2$ lying \emph{below} the $i,k_\mathrm{ML}$ tracer point, 808 so it is this depth 809 \begin{equation} 810 \label{eq:triad:zbase} 811 {z_\mathrm{base}}_{\,i}={z_{w}}_{k_\mathrm{ML}-1/2} 812 \end{equation} 813 (one gridbox deeper than the 814 diagnosed ML depth $z_\mathrm{ML})$ that sets the $h$ used to taper 815 the slopes in \eqref{eq:triad:rmtilde}. 816 \item Finally, we calculate the adjusted triads 817 ${\:}_i^k{\mathbb{R}_\mathrm{ML}}_{\,i_p}^{k_p}$ within the mixed 818 layer, by multiplying the appropriate 819 ${\:}_i{\mathbb{R}_\mathrm{base}}_{\,i_p}^{k_p}$ by the ratio of 820 the depth of the $w$-point ${z_w}_{k+k_p}$ to ${z_\mathrm{base}}_{\,i}$. For 821 instance the green triad centred on $i,k$ 822 \begin{align} 823 {\:}_i^k{\mathbb{R}_\mathrm{ML}}_{\,1/2}^{-1/2} &= 824 \frac{{z_w}_{k-1/2}}{{z_\mathrm{base}}_{\,i}}{\:}_i{\mathbb{R}_\mathrm{base}}_{\,1/2}^{-1/2} 825 \notag \\ 826 \intertext{and more generally} 827 {\:}_i^k{\mathbb{R}_\mathrm{ML}}_{\,i_p}^{k_p} &= 828 \frac{{z_w}_{k+k_p}}{{z_\mathrm{base}}_{\,i}}{\:}_i{\mathbb{R}_\mathrm{base}}_{\,i_p}^{k_p}.\label{eq:triad:RML} 829 \end{align} 830 \end{enumerate} 831 832 % >>>>>>>>>>>>>>>>>>>>>>>>>>>> 833 \begin{figure}[h] 834 \fcapside {\caption{\label{fig:triad:MLB_triad} Definition of 835 mixed-layer depth and calculation of linearly tapered 836 triads. The figure shows a water column at a given $i,j$ 837 (simplified to $i$), with the ocean surface at the top. Tracer points are denoted by 838 bullets, and black lines the edges of the tracer cells; $k$ 839 increases upwards. \\ 840 \hspace{5 em}We define the mixed-layer by setting the vertical index 841 of the tracer point immediately below the mixed layer, 842 $k_\mathrm{ML}$, as the maximum $k$ (shallowest tracer point) 843 such that ${\rho_0}_{i,k}>{\rho_0}_{i,k_{10}}+\Delta\rho_c$, 844 where $i,k_{10}$ is the tracer gridbox within which the depth 845 reaches 10~m. We calculate the triad slopes within the mixed 846 layer by linearly tapering them from zero (at the surface) to 847 the `basal' slopes, the slopes of the four triads passing through the 848 $w$-point $i,k_\mathrm{ML}-1/2$ (blue square), 849 ${\:}_i{\mathbb{R}_\mathrm{base}}_{\,i_p}^{k_p}$. Triads with 850 different $i_p,k_p$, denoted by different colours, (e.g. the green 851 triad $i_p=1/2,k_p=-1/2$) are tapered to the appropriate basal triad.}} 852 {\includegraphics[width=0.60\textwidth]{./TexFiles/Figures/Fig_triad_MLB}} 853 \end{figure} 854 % >>>>>>>>>>>>>>>>>>>>>>>>>>>> 855 856 \subsubsection{Additional truncation of skew iso-neutral flux 857 components} 858 \label{sec:triad:Gerdes-taper} 859 The alternative option is activated by setting \np{ln\_triad\_iso} = 860 true. This retains the same tapered slope $\rML$ described above for the 861 calculation of the $_{33}$ term of the iso-neutral diffusion tensor (the 862 vertical tracer flux driven by vertical tracer gradients), but 863 replaces the $\rML$ in the skew term by 864 \begin{equation} 865 \label{eq:triad:rm*} 866 \rML^*=\left.\rMLt^2\right/\tilde{r}_i-\sigma_i, 867 \end{equation} 868 giving a ML diffusive operator 869 \begin{equation} \label{eq:triad:iso_tensor_ML2} 870 D^{lT}=\nabla {\rm {\bf .}}\left( {A^{lT}\;\Re \;\nabla T} \right) \qquad 871 \mbox{with}\quad \;\;\Re =\left( {{\begin{array}{*{20}c} 872 1 \hfill & 0 \hfill & {-\rML[1]^*}\hfill \\ 873 0 \hfill & 1 \hfill & {-\rML[2]^*} \hfill \\ 874 {-\rML[1]^*}\hfill & {-\rML[2]^*} \hfill & {\rML[1]^2+\rML[2]^2} \hfill \\ 875 \end{array} }} \right). 876 \end{equation} 877 This operator 878 \footnote{To ensure good behaviour where horizontal density 879 gradients are weak, we in fact follow \citet{Gerdes1991} and set 880 $\rML^*=\mathrm{sgn}(\tilde{r}_i)\min(|\rMLt^2/\tilde{r}_i|,|\tilde{r}_i|)-\sigma_i$.} 881 then has the property it gives no vertical density flux, and so does 882 not change the potential energy. 883 This approach is similar to multiplying the iso-neutral diffusion 884 coefficient by $\tilde{r}_\mathrm{max}^{-2}\tilde{r}_i^{-2}$ for steep 885 slopes, as suggested by \citet{Gerdes1991} (see also \citet{Griffies_Bk04}). 886 Again it is applied separately to each triad $_i^k\mathbb{R}_{i_p}^{k_p}$ 887 888 In practice, this approach gives weak vertical tracer fluxes through 889 the mixed-layer, as well as vanishing density fluxes. While it is 890 theoretically advantageous that it does not change the potential 891 energy, it may give a discontinuity between the 892 fluxes within the mixed-layer (purely horizontal) and just below (along 893 iso-neutral surfaces). 894 % This may give strange looking results, 895 % particularly where the mixed-layer depth varies strongly laterally. 513 896 % ================================================================ 514 897 % Skew flux formulation for Eddy Induced Velocity : 515 898 % ================================================================ 516 \section{ Eddy induced velocity and Skew flux formulation} 517 518 When Gent and McWilliams's [1990] diffusion is used (\key{traldf\_eiv} defined), 519 an additional advection term is added. The associated velocity is the so called 899 \section{Eddy induced advection formulated as a skew flux}\label{sec:triad:skew-flux} 900 901 \subsection{The continuous skew flux formulation}\label{sec:triad:continuous-skew-flux} 902 903 When Gent and McWilliams's [1990] diffusion is used, 904 an additional advection term is added. The associated velocity is the so called 520 905 eddy induced velocity, the formulation of which depends on the slopes of iso- 521 neutral surfaces. Contrary to the case of iso-neutral mixing, the slopes used 522 here are referenced to the geopotential surfaces, $i.e.$ \eqref{Eq_ldfslp_geo} 906 neutral surfaces. Contrary to the case of iso-neutral mixing, the slopes used 907 here are referenced to the geopotential surfaces, $i.e.$ \eqref{Eq_ldfslp_geo} 523 908 is used in $z$-coordinate, and the sum \eqref{Eq_ldfslp_geo} 524 + \eqref{Eq_ldfslp_iso} in $z^*$ or $s$-coordinates. 525 526 The eddy induced velocity is given by: 527 \begin{equation} \label{Eq_eiv_v} 909 + \eqref{Eq_ldfslp_iso} in $z^*$ or $s$-coordinates. 910 911 The eddy induced velocity is given by: 912 \begin{subequations} \label{eq:triad:eiv} 913 \begin{equation}\label{eq:triad:eiv_v} 528 914 \begin{split} 529 u^* & = - \frac{1}{e_{ 2}e_{3}}\; \partial_k \left( e_{2} \, A_{e} \; r_i \right)\\530 v^* & = - \frac{1}{e_{ 1}e_{3}}\; \partial_k \left( e_{1} \, A_{e} \; r_j \right)\\531 w^* & = \frac{1}{e_{1}e_{2}}\; \left\{ \partial_i \left( e_{2} \, A_{e} \; r_i \right)532 + \partial_j \left( e_{1} \, A_{e} \;r_j \right) \right\} \\915 u^* & = - \frac{1}{e_{3}}\; \partial_i\psi_1, \\ 916 v^* & = - \frac{1}{e_{3}}\; \partial_j\psi_2, \\ 917 w^* & = \frac{1}{e_{1}e_{2}}\; \left\{ \partial_i \left( e_{2} \, \psi_1\right) 918 + \partial_j \left( e_{1} \, \psi_2\right) \right\}, 533 919 \end{split} 534 920 \end{equation} 535 where $A_{e}$ is the eddy induced velocity coefficient, and $r_i$ and $r_j$ the slopes between the iso-neutral and the geopotential surfaces. 536 537 The traditional way to implement this additional advection is to add it to the Eulerian 538 velocity prior to computing the tracer advection. This allows us to take advantage of 539 all the advection schemes offered for the tracers (see \S\ref{TRA_adv}) and not just 540 a $2^{nd}$ order advection scheme. This is particularly useful for passive tracers 541 where \emph{positivity} of the advection scheme is of paramount importance. 542 543 \citet{Griffies_JPO98} introduces another way to implement the eddy induced advection, 544 the so-called skew form. It is based on a transformation of the advective fluxes 545 using the non-divergent nature of the eddy induced velocity. 546 For example in the (\textbf{i},\textbf{k}) plane, the tracer advective fluxes can be 921 where the streamfunctions $\psi_i$ are given by 922 \begin{equation} \label{eq:triad:eiv_psi} 923 \begin{split} 924 \psi_1 & = A_{e} \; \tilde{r}_1, \\ 925 \psi_2 & = A_{e} \; \tilde{r}_2, 926 \end{split} 927 \end{equation} 928 \end{subequations} 929 with $A_{e}$ the eddy induced velocity coefficient, and $\tilde{r}_1$ and $\tilde{r}_2$ the slopes between the iso-neutral and the geopotential surfaces. 930 931 The traditional way to implement this additional advection is to add 932 it to the Eulerian velocity prior to computing the tracer 933 advection. This is implemented if \key{traldf\_eiv} is set in the 934 default implementation, where \np{ln\_traldf\_grif} is set 935 false. This allows us to take advantage of all the advection schemes 936 offered for the tracers (see \S\ref{TRA_adv}) and not just a $2^{nd}$ 937 order advection scheme. This is particularly useful for passive 938 tracers where \emph{positivity} of the advection scheme is of 939 paramount importance. 940 941 However, when \np{ln\_traldf\_grif} is set true, \NEMO instead 942 implements eddy induced advection according to the so-called skew form 943 \citep{Griffies_JPO98}. It is based on a transformation of the advective fluxes 944 using the non-divergent nature of the eddy induced velocity. 945 For example in the (\textbf{i},\textbf{k}) plane, the tracer advective 946 fluxes per unit area in $ijk$ space can be 547 947 transformed as follows: 548 948 \begin{flalign*} 549 949 \begin{split} 550 \textbf{F}_ {eiv}^T =551 \begin{pmatrix} 950 \textbf{F}_\mathrm{eiv}^T = 951 \begin{pmatrix} 552 952 {e_{2}\,e_{3}\; u^*} \\ 553 953 {e_{1}\,e_{2}\; w^*} \\ 554 954 \end{pmatrix} \; T 555 955 &= 556 \begin{pmatrix} 557 { - \partial_k \left( e_{2} \, A_{e} \; r_i\right) \; T \;} \\558 {+ \partial_i \left( e_{2} \, A_{e} \; r_i\right) \; T \;} \\956 \begin{pmatrix} 957 { - \partial_k \left( e_{2} \,\psi_1 \right) \; T \;} \\ 958 {+ \partial_i \left( e_{2} \, \psi_1 \right) \; T \;} \\ 559 959 \end{pmatrix} \\ 560 &= 561 \begin{pmatrix} 562 { - \partial_k \left( e_{2} \, A_{e} \; r_i\; T \right) \;} \\563 {+ \partial_i \left( e_{2} \, A_{e} \; r_i\; T \right) \;} \\564 \end{pmatrix} 565 + 566 \begin{pmatrix} 567 {+ e_{2} \, A_{e} \; r_i\; \partial_k T} \\568 { - e_{2} \, A_{e} \; r_i\; \partial_i T} \\569 \end{pmatrix} 960 &= 961 \begin{pmatrix} 962 { - \partial_k \left( e_{2} \, \psi_1 \; T \right) \;} \\ 963 {+ \partial_i \left( e_{2} \,\psi_1 \; T \right) \;} \\ 964 \end{pmatrix} 965 + 966 \begin{pmatrix} 967 {+ e_{2} \, \psi_1 \; \partial_k T} \\ 968 { - e_{2} \, \psi_1 \; \partial_i T} \\ 969 \end{pmatrix} 570 970 \end{split} 571 971 \end{flalign*} 572 and since the eddy induce s velocity field is no-divergent, we end up with the skew573 form of the eddy induced advective fluxes :574 \begin{equation} \label{ Eq_eiv_skew_continuous}575 \textbf{F}_ {eiv}^T = \begin{pmatrix}576 {+ e_{2} \, A_{e} \; r_i\; \partial_k T} \\577 { - e_{2} \, A_{e} \; r_i\; \partial_i T} \\972 and since the eddy induced velocity field is non-divergent, we end up with the skew 973 form of the eddy induced advective fluxes per unit area in $ijk$ space: 974 \begin{equation} \label{eq:triad:eiv_skew_ijk} 975 \textbf{F}_\mathrm{eiv}^T = \begin{pmatrix} 976 {+ e_{2} \, \psi_1 \; \partial_k T} \\ 977 { - e_{2} \, \psi_1 \; \partial_i T} \\ 578 978 \end{pmatrix} 579 979 \end{equation} 580 The tendency associated with eddy induced velocity is then simply the divergence 581 of the \eqref{Eq_eiv_skew_continuous} fluxes. It naturally conserves the tracer 582 content, as it is expressed in flux form. It also preserve the tracer variance. 583 584 The discrete form of \eqref{Eq_eiv_skew_continuous} using the slopes \eqref{Gf_slopes} and defining $A_e$ at $T$-point is then given by: 585 \begin{flalign} \label{Eq_eiv_skew} \begin{split} 586 \textbf{F}_{eiv}^T \equiv 587 \sum_{\substack{i_p,\,k_p}} \begin{pmatrix} 588 +{e_{2u}}_{i+1/2-i_p}^{k} \ {A_{e}}_{i+1/2-i_p}^{k} 589 \ \ { _{i+1/2-i_p}^k \mathbb{R}_{i_p}^{k_p} } \ \ \delta_{k+k_p}[T_{i+1/2-i_p}] \\ 590 \\ 591 - {e_{2u}}_i^{k+1/2-k_p} \ {A_{e}}_i^{k+1/2-k_p} 592 \ \ { _i^{k+1/2-k_p} \mathbb{R}_{i_p}^{k_p} } \ \delta_{i+i_p}[T^{k+1/2-k_p}] \\ 593 \end{pmatrix} 594 \end{split} \end{flalign} 595 Note that \eqref{Eq_eiv_skew} is valid in $z$-coordinate with or without partial cells. In $z^*$ or $s$-coordinate, the the slope between the level and the geopotential surfaces must be added to $\mathbb{R}$ for the discret form to be exact. 596 597 Such a choice of discretisation is consistent with the iso-neutral operator as it uses the same definition for the slopes. It also ensures the conservation of the tracer variance (see Appendix \ref{Apdx_eiv_skew}), $i.e.$ it does not include a diffusive component but is a `pure' advection term. 598 599 600 601 602 \newpage %force an empty line 603 % ================================================================ 604 % Discrete Invariants of the skew flux formulation 605 % ================================================================ 606 \subsection{Discrete Invariants of the skew flux formulation} 607 \label{Apdx_eiv_skew} 608 609 610 Demonstration for the conservation of the tracer variance in the (\textbf{i},\textbf{j}) plane. 611 612 This have to be moved in an Appendix. 613 614 The continuous property to be demonstrated is : 615 \begin{align*} 616 \int_D \nabla \cdot \textbf{F}_{eiv}(T) \; T \;dv \equiv 0 617 \end{align*} 618 The discrete form of its left hand side is obtained using \eqref{Eq_eiv_skew} 619 \begin{align*} 620 \sum\limits_{i,k} \sum_{\substack{i_p,\,k_p}} \Biggl\{ \;\; 621 \delta_i &\left[ 622 {e_{2u}}_{i+i_p+1/2}^{k} \;\ \ {A_{e}}_{i+i_p+1/2}^{k} 623 \ \ \ { _{i+i_p+1/2}^k \mathbb{R}_{-i_p}^{k_p} } \quad \delta_{k+k_p}[T_{i+i_p+1/2}] 624 \right] \; T_i^k \\ 625 - \delta_k &\left[ 626 {e_{2u}}_i^{k+k_p+1/2} \ \ {A_{e}}_i^{k+k_p+1/2} 627 \ \ { _i^{k+k_p+1/2} \mathbb{R}_{i_p}^{-k_p} } \ \ \delta_{i+i_p}[T^{k+k_p+1/2}] 628 \right] \; T_i^k \ \Biggr\} 629 \end{align*} 630 apply the adjoint of delta operator, it becomes 631 \begin{align*} 632 \sum\limits_{i,k} \sum_{\substack{i_p,\,k_p}} \Biggl\{ \;\; 633 &\left( 634 {e_{2u}}_{i+i_p+1/2}^{k} \;\ \ {A_{e}}_{i+i_p+1/2}^{k} 635 \ \ \ { _{i+i_p+1/2}^k \mathbb{R}_{-i_p}^{k_p} } \quad \delta_{k+k_p}[T_{i+i_p+1/2}] 636 \right) \; \delta_{i+1/2}[T^{k}] \\ 637 - &\left( 638 {e_{2u}}_i^{k+k_p+1/2} \ \ {A_{e}}_i^{k+k_p+1/2} 639 \ \ { _i^{k+k_p+1/2} \mathbb{R}_{i_p}^{-k_p} } \ \ \delta_{i+i_p}[T^{k+k_p+1/2}] 640 \right) \; \delta_{k+1/2}[T_{i}] \ \Biggr\} 641 \end{align*} 642 Expending the summation on $i_p$ and $k_p$, it becomes: 643 \begin{align*} 644 \begin{matrix} 645 &\sum\limits_{i,k} \Bigl\{ 646 &+{e_{2u}}_{i+1}^{k} &{A_{e}}_{i+1 }^{k} 647 &\ {_{i+1}^k \mathbb{R}_{- 1/2}^{-1/2}} &\delta_{k-1/2}[T_{i+1}] &\delta_{i+1/2}[T^{k}] &\\ 648 &&+{e_{2u}}_i^{k\ \ \ \:} &{A_{e}}_{i}^{k\ \ \ \:} 649 &\ {\ \ \;_i^k \mathbb{R}_{+1/2}^{-1/2}} &\delta_{k-1/2}[T_{i\ \ \ \;}] &\delta_{i+1/2}[T^{k}] &\\ 650 &&+{e_{2u}}_{i+1}^{k} &{A_{e}}_{i+1 }^{k} 651 &\ {_{i+1}^k \mathbb{R}_{- 1/2}^{+1/2}} &\delta_{k+1/2}[T_{i+1}] &\delta_{i+1/2}[T^{k}] &\\ 652 &&+{e_{2u}}_i^{k\ \ \ \:} &{A_{e}}_{i}^{k\ \ \ \:} 653 &\ {\ \ \;_i^k \mathbb{R}_{+1/2}^{+1/2}} &\delta_{k+1/2}[T_{i\ \ \ \;}] &\delta_{i+1/2}[T^{k}] &\\ 654 % 655 &&-{e_{2u}}_i^{k+1} &{A_{e}}_i^{k+1} 656 &{_i^{k+1} \mathbb{R}_{-1/2}^{- 1/2}} &\delta_{i-1/2}[T^{k+1}] &\delta_{k+1/2}[T_{i}] &\\ 657 &&-{e_{2u}}_i^{k\ \ \ \:} &{A_{e}}_i^{k\ \ \ \:} 658 &{\ \ \;_i^k \mathbb{R}_{-1/2}^{+1/2}} &\delta_{i-1/2}[T^{k\ \ \ \:}] &\delta_{k+1/2}[T_{i}] &\\ 659 &&-{e_{2u}}_i^{k+1 } &{A_{e}}_i^{k+1} 660 &{_i^{k+1} \mathbb{R}_{+1/2}^{- 1/2}} &\delta_{i+1/2}[T^{k+1}] &\delta_{k+1/2}[T_{i}] &\\ 661 &&-{e_{2u}}_i^{k\ \ \ \:} &{A_{e}}_i^{k\ \ \ \:} 662 &{\ \ \;_i^k \mathbb{R}_{+1/2}^{+1/2}} &\delta_{i+1/2}[T^{k\ \ \ \:}] &\delta_{k+1/2}[T_{i}] 663 &\Bigr\} \\ 664 \end{matrix} 665 \end{align*} 666 The two terms associated with the triad ${_i^k \mathbb{R}_{+1/2}^{+1/2}}$ are the 667 same but of opposite signs, they cancel out. 668 Exactly the same thing occurs for the triad ${_i^k \mathbb{R}_{-1/2}^{-1/2}}$. 669 The two terms associated with the triad ${_i^k \mathbb{R}_{+1/2}^{-1/2}}$ are the 670 same but both of opposite signs and shifted by 1 in $k$ direction. When summing over $k$ 671 they cancel out with the neighbouring grid points. 672 Exactly the same thing occurs for the triad ${_i^k \mathbb{R}_{-1/2}^{+1/2}}$ in the 673 $i$ direction. Therefore the sum over the domain is zero, $i.e.$ the variance of the 674 tracer is preserved by the discretisation of the skew fluxes. 675 676 %%% Local Variables: 677 %%% TeX-master: "../../NEMO_book.tex" 678 %%% End: 980 The total fluxes per unit physical area are then 981 \begin{equation}\label{eq:triad:eiv_skew_physical} 982 \begin{split} 983 f^*_1 & = \frac{1}{e_{3}}\; \psi_1 \partial_k T \\ 984 f^*_2 & = \frac{1}{e_{3}}\; \psi_2 \partial_k T \\ 985 f^*_3 & = -\frac{1}{e_{1}e_{2}}\; \left\{ e_{2} \psi_1 \partial_i T 986 + e_{1} \psi_2 \partial_j T \right\}. \\ 987 \end{split} 988 \end{equation} 989 Note that Eq.~ \eqref{eq:triad:eiv_skew_physical} takes the same form whatever the 990 vertical coordinate, though of course the slopes 991 $\tilde{r}_i$ which define the $\psi_i$ in \eqref{eq:triad:eiv_psi} are relative to geopotentials. 992 The tendency associated with eddy induced velocity is then simply the convergence 993 of the fluxes (\ref{eq:triad:eiv_skew_ijk}, \ref{eq:triad:eiv_skew_physical}), so 994 \begin{equation} \label{eq:triad:skew_eiv_conv} 995 \frac{\partial T}{\partial t}= -\frac{1}{e_1 \, e_2 \, e_3 } \left[ 996 \frac{\partial}{\partial i} \left( e_2 \psi_1 \partial_k T\right) 997 + \frac{\partial}{\partial j} \left( e_1 \; 998 \psi_2 \partial_k T\right) 999 - \frac{\partial}{\partial k} \left( e_{2} \psi_1 \partial_i T 1000 + e_{1} \psi_2 \partial_j T \right) \right] 1001 \end{equation} 1002 It naturally conserves the tracer content, as it is expressed in flux 1003 form. Since it has the same divergence as the advective form it also 1004 preserves the tracer variance. 1005 1006 \subsection{The discrete skew flux formulation} 1007 The skew fluxes in (\ref{eq:triad:eiv_skew_physical}, \ref{eq:triad:eiv_skew_ijk}), like the off-diagonal terms 1008 (\ref{eq:triad:i13c}, \ref{eq:triad:i31c}) of the small angle diffusion tensor, are best 1009 expressed in terms of the triad slopes, as in Fig.~\ref{fig:triad:ISO_triad} 1010 and Eqs~(\ref{eq:triad:i13}, \ref{eq:triad:i31}); but now in terms of the triad slopes 1011 $\tilde{\mathbb{R}}$ relative to geopotentials instead of the 1012 $\mathbb{R}$ relative to coordinate surfaces. The discrete form of 1013 \eqref{eq:triad:eiv_skew_ijk} using the slopes \eqref{eq:triad:R} and 1014 defining $A_e$ at $T$-points is then given by: 1015 1016 1017 \begin{subequations}\label{eq:triad:allskewflux} 1018 \begin{flalign}\label{eq:triad:vect_skew_flux} 1019 \vect{F}_\mathrm{eiv}(T) &\equiv 1020 \sum_{\substack{i_p,\,k_p}} 1021 \begin{pmatrix} 1022 {_{i+1/2-i_p}^k {\mathbb{S}_u}_{i_p}^{k_p} } (T) \\ 1023 \\ 1024 {_i^{k+1/2-k_p} {\mathbb{S}_w}_{i_p}^{k_p} } (T) \\ 1025 \end{pmatrix}, 1026 \end{flalign} 1027 where the skew flux in the $i$-direction associated with a given 1028 triad is (\ref{eq:triad:latflux-triad}, \ref{eq:triad:triadfluxu}): 1029 \begin{align} 1030 \label{eq:triad:skewfluxu} 1031 _i^k {\mathbb{S}_u}_{i_p}^{k_p} (T) &= + \quarter {A_e}_i^k{ 1032 \:}\frac{{b_u}_{i+i_p}^k}{{e_{1u}}_{\,i + i_p}^{\,k}} 1033 \ {_i^k\tilde{\mathbb{R}}_{i_p}^{k_p}} \ 1034 \frac{ \delta_{k+k_p} [T^i] }{{e_{3w}}_{\,i}^{\,k+k_p} }, 1035 \\ 1036 \intertext{and \eqref{eq:triad:triadfluxw} in the $k$-direction, changing the sign 1037 to be consistent with \eqref{eq:triad:eiv_skew_ijk}:} 1038 _i^k {\mathbb{S}_w}_{i_p}^{k_p} (T) 1039 &= -\quarter {A_e}_i^k{\: }\frac{{b_u}_{i+i_p}^k}{{e_{3w}}_{\,i}^{\,k+k_p}} 1040 {_i^k\tilde{\mathbb{R}}_{i_p}^{k_p}}\frac{ \delta_{i+ i_p}[T^k] }{ {e_{1u}}_{\,i + i_p}^{\,k} }.\label{eq:triad:skewfluxw} 1041 \end{align} 1042 \end{subequations} 1043 1044 Such a discretisation is consistent with the iso-neutral 1045 operator as it uses the same definition for the slopes. It also 1046 ensures the following two key properties. 1047 \subsubsection{No change in tracer variance} 1048 The discretization conserves tracer variance, $i.e.$ it does not 1049 include a diffusive component but is a `pure' advection term. This can 1050 be seen 1051 %either from Appendix \ref{Apdx_eiv_skew} or 1052 by considering the 1053 fluxes associated with a given triad slope 1054 $_i^k{\mathbb{R}}_{i_p}^{k_p} (T)$. For, following 1055 \S\ref{sec:triad:variance} and \eqref{eq:triad:dvar_iso_i}, the 1056 associated horizontal skew-flux $_i^k{\mathbb{S}_u}_{i_p}^{k_p} (T)$ 1057 drives a net rate of change of variance, summed over the two 1058 $T$-points $i+i_p-\half,k$ and $i+i_p+\half,k$, of 1059 \begin{equation} 1060 \label{eq:triad:dvar_eiv_i} 1061 _i^k{\mathbb{S}_u}_{i_p}^{k_p} (T)\,\delta_{i+ i_p}[T^k], 1062 \end{equation} 1063 while the associated vertical skew-flux gives a variance change summed over the 1064 $T$-points $i,k+k_p-\half$ (above) and $i,k+k_p+\half$ (below) of 1065 \begin{equation} 1066 \label{eq:triad:dvar_eiv_k} 1067 _i^k{\mathbb{S}_w}_{i_p}^{k_p} (T) \,\delta_{k+ k_p}[T^i]. 1068 \end{equation} 1069 Inspection of the definitions (\ref{eq:triad:skewfluxu}, \ref{eq:triad:skewfluxw}) 1070 shows that these two variance changes (\ref{eq:triad:dvar_eiv_i}, \ref{eq:triad:dvar_eiv_k}) 1071 sum to zero. Hence the two fluxes associated with each triad make no 1072 net contribution to the variance budget. 1073 1074 \subsubsection{Reduction in gravitational PE} 1075 The vertical density flux associated with the vertical skew-flux 1076 always has the same sign as the vertical density gradient; thus, so 1077 long as the fluid is stable (the vertical density gradient is 1078 negative) the vertical density flux is negative (downward) and hence 1079 reduces the gravitational PE. 1080 1081 For the change in gravitational PE driven by the $k$-flux is 1082 \begin{align} 1083 \label{eq:triad:vert_densityPE} 1084 g {e_{3w}}_{\,i}^{\,k+k_p}{\mathbb{S}_w}_{i_p}^{k_p} (\rho) 1085 &=g {e_{3w}}_{\,i}^{\,k+k_p}\left[-\alpha _i^k {\:}_i^k 1086 {\mathbb{S}_w}_{i_p}^{k_p} (T) + \beta_i^k {\:}_i^k 1087 {\mathbb{S}_w}_{i_p}^{k_p} (S) \right]. \notag \\ 1088 \intertext{Substituting ${\:}_i^k {\mathbb{S}_w}_{i_p}^{k_p}$ from 1089 \eqref{eq:triad:skewfluxw}, gives} 1090 % and separating out 1091 % $\rtriadt{R}=\rtriad{R} + \delta_{i+i_p}[z_T^k]$, 1092 % gives two terms. The 1093 % first $\rtriad{R}$ term (the only term for $z$-coordinates) is: 1094 &=-\quarter g{A_e}_i^k{\: }{b_u}_{i+i_p}^k {_i^k\tilde{\mathbb{R}}_{i_p}^{k_p}} 1095 \frac{ -\alpha _i^k\delta_{i+ i_p}[T^k]+ \beta_i^k\delta_{i+ i_p}[S^k]} { {e_{1u}}_{\,i + i_p}^{\,k} } \notag \\ 1096 &=+\quarter g{A_e}_i^k{\: }{b_u}_{i+i_p}^k 1097 \left({_i^k\mathbb{R}_{i_p}^{k_p}}+\frac{\delta_{i+i_p}[z_T^k]}{{e_{1u}}_{\,i + i_p}^{\,k}}\right) {_i^k\mathbb{R}_{i_p}^{k_p}} 1098 \frac{-\alpha_i^k \delta_{k+ k_p}[T^i]+ \beta_i^k\delta_{k+ k_p}[S^i]} {{e_{3w}}_{\,i}^{\,k+k_p}}, 1099 \end{align} 1100 using the definition of the triad slope $\rtriad{R}$, 1101 \eqref{eq:triad:R} to express $-\alpha _i^k\delta_{i+ i_p}[T^k]+ 1102 \beta_i^k\delta_{i+ i_p}[S^k]$ in terms of $-\alpha_i^k \delta_{k+ 1103 k_p}[T^i]+ \beta_i^k\delta_{k+ k_p}[S^i]$. 1104 1105 Where the coordinates slope, the $i$-flux gives a PE change 1106 \begin{multline} 1107 \label{eq:triad:lat_densityPE} 1108 g \delta_{i+i_p}[z_T^k] 1109 \left[ 1110 -\alpha _i^k {\:}_i^k {\mathbb{S}_u}_{i_p}^{k_p} (T) + \beta_i^k {\:}_i^k {\mathbb{S}_u}_{i_p}^{k_p} (S) 1111 \right] \\ 1112 = +\quarter g{A_e}_i^k{\: }{b_u}_{i+i_p}^k 1113 \frac{\delta_{i+i_p}[z_T^k]}{{e_{1u}}_{\,i + i_p}^{\,k}} 1114 \left({_i^k\mathbb{R}_{i_p}^{k_p}}+\frac{\delta_{i+i_p}[z_T^k]}{{e_{1u}}_{\,i + i_p}^{\,k}}\right) 1115 \frac{-\alpha_i^k \delta_{k+ k_p}[T^i]+ \beta_i^k\delta_{k+ k_p}[S^i]} {{e_{3w}}_{\,i}^{\,k+k_p}}, 1116 \end{multline} 1117 (using \eqref{eq:triad:skewfluxu}) and so the total PE change 1118 \eqref{eq:triad:vert_densityPE} + \eqref{eq:triad:lat_densityPE} associated with the triad fluxes is 1119 \begin{multline} 1120 \label{eq:triad:tot_densityPE} 1121 g{e_{3w}}_{\,i}^{\,k+k_p}{\mathbb{S}_w}_{i_p}^{k_p} (\rho) + 1122 g\delta_{i+i_p}[z_T^k] {\:}_i^k {\mathbb{S}_u}_{i_p}^{k_p} (\rho) \\ 1123 = +\quarter g{A_e}_i^k{\: }{b_u}_{i+i_p}^k 1124 \left({_i^k\mathbb{R}_{i_p}^{k_p}}+\frac{\delta_{i+i_p}[z_T^k]}{{e_{1u}}_{\,i + i_p}^{\,k}}\right)^2 1125 \frac{-\alpha_i^k \delta_{k+ k_p}[T^i]+ \beta_i^k\delta_{k+ k_p}[S^i]} {{e_{3w}}_{\,i}^{\,k+k_p}}. 1126 \end{multline} 1127 Where the fluid is stable, with $-\alpha_i^k \delta_{k+ k_p}[T^i]+ 1128 \beta_i^k\delta_{k+ k_p}[S^i]<0$, this PE change is negative. 1129 1130 \subsection{Treatment of the triads at the boundaries}\label{sec:triad:skew_bdry} 1131 Triad slopes \rtriadt{R} used for the calculation of the eddy-induced skew-fluxes 1132 are masked at the boundaries in exactly the same way as are the triad 1133 slopes \rtriad{R} used for the iso-neutral diffusive fluxes, as 1134 described in \S\ref{sec:triad:iso_bdry} and 1135 Fig.~\ref{fig:triad:bdry_triads}. Thus surface layer triads 1136 $\triadt{i}{1}{R}{1/2}{-1/2}$ and $\triadt{i+1}{1}{R}{-1/2}{-1/2}$ are 1137 masked, and both near bottom triad slopes $\triadt{i}{k}{R}{1/2}{1/2}$ 1138 and $\triadt{i+1}{k}{R}{-1/2}{1/2}$ are masked when either of the 1139 $i,k+1$ or $i+1,k+1$ tracer points is masked, i.e.\ the $i,k+1$ 1140 $u$-point is masked. The namelist parameter \np{ln\_botmix\_grif} has 1141 no effect on the eddy-induced skew-fluxes. 1142 1143 \subsection{ Limiting of the slopes within the interior}\label{sec:triad:limitskew} 1144 Presently, the iso-neutral slopes $\tilde{r}_i$ relative 1145 to geopotentials are limited to be less than $1/100$, exactly as in 1146 calculating the iso-neutral diffusion, \S \ref{sec:triad:limit}. Each 1147 individual triad \rtriadt{R} is so limited. 1148 1149 \subsection{Tapering within the surface mixed layer}\label{sec:triad:taperskew} 1150 The slopes $\tilde{r}_i$ relative to 1151 geopotentials (and thus the individual triads \rtriadt{R}) are always tapered linearly from their value immediately below the mixed layer to zero at the 1152 surface \eqref{eq:triad:rmtilde}, as described in \S\ref{sec:triad:lintaper}. This is 1153 option (c) of Fig.~\ref{Fig_eiv_slp}. This linear tapering for the 1154 slopes used to calculate the eddy-induced fluxes is 1155 unaffected by the value of \np{ln\_triad\_iso}. 1156 1157 The justification for this linear slope tapering is that, for $A_e$ 1158 that is constant or varies only in the horizontal (the most commonly 1159 used options in \NEMO: see \S\ref{LDF_coef}), it is 1160 equivalent to a horizontal eiv (eddy-induced velocity) that is uniform 1161 within the mixed layer \eqref{eq:triad:eiv_v}. This ensures that the 1162 eiv velocities do not restratify the mixed layer \citep{Treguier1997, 1163 Danabasoglu_al_2008}. Equivantly, in terms 1164 of the skew-flux formulation we use here, the 1165 linear slope tapering within the mixed-layer gives a linearly varying 1166 vertical flux, and so a tracer convergence uniform in depth (the 1167 horizontal flux convergence is relatively insignificant within the mixed-layer). 1168 1169 \subsection{Streamfunction diagnostics}\label{sec:triad:sfdiag} 1170 Where the namelist parameter \np{ln\_traldf\_gdia}=true, diagnosed 1171 mean eddy-induced velocities are output. Each time step, 1172 streamfunctions are calculated in the $i$-$k$ and $j$-$k$ planes at 1173 $uw$ (integer +1/2 $i$, integer $j$, integer +1/2 $k$) and $vw$ 1174 (integer $i$, integer +1/2 $j$, integer +1/2 $k$) points (see Table 1175 \ref{Tab_cell}) respectively. We follow \citep{Griffies_Bk04} and 1176 calculate the streamfunction at a given $uw$-point from the 1177 surrounding four triads according to: 1178 \begin{equation} 1179 \label{eq:triad:sfdiagi} 1180 {\psi_1}_{i+1/2}^{k+1/2}={\quarter}\sum_{\substack{i_p,\,k_p}} 1181 {A_e}_{i+1/2-i_p}^{k+1/2-k_p}\:\triadd{i+1/2-i_p}{k+1/2-k_p}{R}{i_p}{k_p}. 1182 \end{equation} 1183 The streamfunction $\psi_1$ is calculated similarly at $vw$ points. 1184 The eddy-induced velocities are then calculated from the 1185 straightforward discretisation of \eqref{eq:triad:eiv_v}: 1186 \begin{equation}\label{eq:triad:eiv_v_discrete} 1187 \begin{split} 1188 {u^*}_{i+1/2}^{k} & = - \frac{1}{{e_{3u}}_{i}^{k}}\left({\psi_1}_{i+1/2}^{k+1/2}-{\psi_1}_{i+1/2}^{k+1/2}\right), \\ 1189 {v^*}_{j+1/2}^{k} & = - \frac{1}{{e_{3v}}_{j}^{k}}\left({\psi_2}_{j+1/2}^{k+1/2}-{\psi_2}_{j+1/2}^{k+1/2}\right), \\ 1190 {w^*}_{i,j}^{k+1/2} & = \frac{1}{e_{1t}e_{2t}}\; \left\{ 1191 {e_{2u}}_{i+1/2}^{k+1/2} \,{\psi_1}_{i+1/2}^{k+1/2} - 1192 {e_{2u}}_{i-1/2}^{k+1/2} \,{\psi_1}_{i-1/2}^{k+1/2} \right. + \\ 1193 \phantom{=} & \qquad\qquad\left. {e_{2v}}_{j+1/2}^{k+1/2} \,{\psi_2}_{j+1/2}^{k+1/2} - {e_{2v}}_{j-1/2}^{k+1/2} \,{\psi_2}_{j-1/2}^{k+1/2} \right\}, 1194 \end{split} 1195 \end{equation} -
trunk/DOC/TexFiles/Chapters/Chap_ASM.tex
r2483 r3294 15 15 The ASM code adds the functionality to apply increments to the model variables: 16 16 temperature, salinity, sea surface height, velocity and sea ice concentration. 17 These are read into the model from a NetCDF file which may be produced by data18 assimilation . The code can also output model background fields which are used17 These are read into the model from a NetCDF file which may be produced by separate data 18 assimilation code. The code can also output model background fields which are used 19 19 as an input to data assimilation code. This is all controlled by the namelist 20 20 \textit{nam\_asminc}. There is a brief description of all the namelist options … … 86 86 87 87 %========================================================================== 88 % Divergence damping description %%% 89 \section{Divergence damping initialisation} 90 \label{ASM_details} 91 92 The velocity increments may be initialized by the iterative application of 93 a divergence damping operator. In iteration step $n$ new estimates of 94 velocity increments $u^{n}_I$ and $v^{n}_I$ are updated by: 95 \begin{equation} \label{eq:asm_dmp} 96 \left\{ \begin{aligned} 97 u^{n}_I = u^{n-1}_I + \frac{1}{e_{1u} } \delta _{i+1/2} \left( {A_D 98 \;\chi^{n-1}_I } \right) \\ 99 \\ 100 v^{n}_I = v^{n-1}_I + \frac{1}{e_{2v} } \delta _{j+1/2} \left( {A_D 101 \;\chi^{n-1}_I } \right) \\ 102 \end{aligned} \right., 103 \end{equation} 104 where 105 \begin{equation} \label{eq:asm_div} 106 \chi^{n-1}_I = \frac{1}{e_{1t}\,e_{2t}\,e_{3t} } 107 \left( {\delta _i \left[ {e_{2u}\,e_{3u}\,u^{n-1}_I} \right] 108 +\delta _j \left[ {e_{1v}\,e_{3v}\,v^{n-1}_I} \right]} \right). 109 \end{equation} 110 By the application of \eqref{eq:asm_dmp} and \eqref{eq:asm_dmp} the divergence is filtered 111 in each iteration, and the vorticity is left unchanged. In the presence of coastal boundaries 112 with zero velocity increments perpendicular to the coast the divergence is strongly damped. 113 This type of the initialisation reduces the vertical velocity magnitude and alleviates the 114 problem of the excessive unphysical vertical mixing in the first steps of the model 115 integration \citep{Talagrand_JAS72, Dobricic_al_OS07}. Diffusion coefficients are defined as 116 $A_D = \alpha e_{1t} e_{2t}$, where $\alpha = 0.2$. The divergence damping is activated by 117 assigning to \np{nn\_divdmp} in the \textit{nam\_asminc} namelist a value greater than zero. 118 By choosing this value to be of the order of 100 the increments in the vertical velocity will 119 be significantly reduced. 120 121 122 %========================================================================== 88 123 89 124 \section{Implementation details} -
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r2541 r3294 219 219 at $\sim 30\deg$N and rotated by 45\deg, 3180~km long, 2120~km wide 220 220 and 4~km deep (Fig.~\ref{Fig_MISC_strait_hand}). 221 The domain is bounded by vertical walls and by a ßat bottom. The configuration is221 The domain is bounded by vertical walls and by a flat bottom. The configuration is 222 222 meant to represent an idealized North Atlantic or North Pacific basin. 223 The circulation is forced by analytical profiles of wind and buoyancy ßuxes.223 The circulation is forced by analytical profiles of wind and buoyancy fluxes. 224 224 The applied forcings vary seasonally in a sinusoidal manner between winter 225 225 and summer extrema \citep{Levy_al_OM10}. … … 227 227 It forces a subpolar gyre in the north, a subtropical gyre in the wider part of the domain 228 228 and a small recirculation gyre in the southern corner. 229 The net heat ßux takes the form of a restoring toward a zonal apparent air230 temperature profile. A portion of the net heat ßux which comes from the solar radiation229 The net heat flux takes the form of a restoring toward a zonal apparent air 230 temperature profile. A portion of the net heat flux which comes from the solar radiation 231 231 is allowed to penetrate within the water column. 232 The fresh water ßux is also prescribed and varies zonally.233 It is determined such as, at each time step, the basin-integrated ßux is zero.232 The fresh water flux is also prescribed and varies zonally. 233 It is determined such as, at each time step, the basin-integrated flux is zero. 234 234 The basin is initialised at rest with vertical profiles of temperature and salinity 235 235 uniformly applied to the whole domain. … … 269 269 270 270 % ------------------------------------------------------------------------------------------------------------- 271 % POMME configuration 272 % ------------------------------------------------------------------------------------------------------------- 273 \section{POMME: mid-latitude sub-domain} 274 \label{MISC_config_POMME} 275 276 277 \key{pomme\_r025} : to be described.... 278 279 280 271 % AMM configuration 272 % ------------------------------------------------------------------------------------------------------------- 273 \section{AMM: atlantic margin configuration (\key{amm\_12km})} 274 \label{MISC_config_AMM} 275 276 The AMM, Atlantic Margins Model, is a regional model covering the 277 Northwest European Shelf domain on a regular lat-lon grid at 278 approximately 12km horizontal resolution. The key \key{amm\_12km} 279 is used to create the correct dimensions of the AMM domain. 280 281 This configuration tests several features of NEMO functionality specific 282 to the shelf seas. 283 In particular, the AMM uses $S$-coordinates in the vertical rather than 284 $z$-coordinates and is forced with tidal lateral boundary conditions 285 using a flather boundary condition from the BDY module (key\_bdy). 286 The AMM configuration uses the GLS (key\_zdfgls) turbulence scheme, the 287 VVL non-linear free surface(key\_vvl) and time-splitting 288 (key\_dynspg\_ts). 289 290 In addition to the tidal boundary condition the model may also take 291 open boundary conditions from a North Atlantic model. Boundaries may be 292 completely ommited by removing the BDY key (key\_bdy). 293 Sample surface fluxes, river forcing and a sample initial restart file 294 are included to test a realistic model run. The Baltic boundary is 295 included within the river input file and is specified as a river source. 296 Unlike ordinary river points the Baltic inputs also include salinity and 297 temperature data. 298 -
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trunk/DOC/TexFiles/Chapters/Chap_DIA.tex
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r2541 r3294 236 236 \item[group]: define a group of file or field. Accept the same attributes as file or field. 237 237 238 \item[file]: define the output file Õs characteristics. Accepted attributes are description, enable,238 \item[file]: define the output file's characteristics. Accepted attributes are description, enable, 239 239 output\_freq, output\_level, id, name, name\_suffix. Child of file\_definition or group of files tag. 240 240 … … 321 321 \item[output\_level]: file attribute. Integer from 0 to 10 defining the output priority of variables in a file: 322 322 all variables listed in the file with a level smaller or equal to output\_level will be output. 323 Other variables won Õt be output even if they are listed in the file.323 Other variables won't be output even if they are listed in the file. 324 324 325 325 \item[positive]: axis attribute (always .FALSE.). Logical defining the vertical axis convention used … … 681 681 numeric of the code, so that the trajectories never intercept the bathymetry. 682 682 683 \subsubsection{ Input data: initial coordinates } 684 685 Initial coordinates can be given with Ariane Tools convention ( IJK coordinates ,(\np{ln\_ariane}=true) ) 686 or with longitude and latitude. 687 688 689 In case of Ariane convention, input filename is \np{"init\_float\_ariane"}. Its format is: 690 691 \texttt{ I J K nisobfl itrash itrash } 692 693 \noindent with: 694 695 - I,J,K : indexes of initial position 696 697 - nisobfl: 0 for an isobar float, 1 for a float following the w velocity 698 699 - itrash : set to zero; it is a dummy variable to respect Ariane Tools convention 700 701 - itrash :set to zero; it is a dummy variable to respect Ariane Tools convention 702 703 \noindent Example:\\ 704 \noindent \texttt{ 100.00000 90.00000 -1.50000 1.00000 0.00000}\\ 705 \texttt{ 102.00000 90.00000 -1.50000 1.00000 0.00000}\\ 706 \texttt{ 104.00000 90.00000 -1.50000 1.00000 0.00000}\\ 707 \texttt{ 106.00000 90.00000 -1.50000 1.00000 0.00000}\\ 708 \texttt{ 108.00000 90.00000 -1.50000 1.00000 0.00000}\\ 709 710 711 In the other case ( longitude and latitude ), input filename is \np{"init\_float"}. Its format is: 712 713 \texttt{ Long Lat depth nisobfl ngrpfl itrash} 714 715 \noindent with: 716 717 - Long, Lat, depth : Longitude, latitude, depth 718 719 - nisobfl: 0 for an isobar float, 1 for a float following the w velocity 720 721 - ngrpfl : number to identify searcher group 722 723 - itrash :set to 1; it is a dummy variable. 724 725 \noindent Example: 726 727 \noindent\texttt{ 20.0 0.0 0.0 0 1 1 }\\ 728 \texttt{ -21.0 0.0 0.0 0 1 1 }\\ 729 \texttt{ -22.0 0.0 0.0 0 1 1 }\\ 730 \texttt{ -23.0 0.0 0.0 0 1 1 }\\ 731 \texttt{ -24.0 0.0 0.0 0 1 1 }\\ 732 733 \np{jpnfl} is the total number of floats during the run. 734 When initial positions are read in a restart file ( \np{ln\_rstflo= .TRUE.} ), \np{jpnflnewflo} 735 can be added in the initialization file. 736 737 \subsubsection{ Output data } 738 739 \np{nn\_writefl} is the frequency of writing in float output file and \np{nn\_stockfl} 740 is the frequency of creation of the float restart file. 741 742 Output data can be written in ascii files (\np{ln\_flo\_ascii = .TRUE.} ). In that case, 743 output filename is \np{is trajec\_float}. 744 745 Another possiblity of writing format is Netcdf (\np{ln\_flo\_ascii = .FALSE.} ). There are 2 possibilities: 746 747 - if (\key{iomput}) is used, outputs are selected in \np{iodef.xml}. Here it is an example of specification 748 to put in files description section: 749 750 \vspace{-30pt} 751 \begin{alltt} {{\scriptsize 752 \begin{verbatim} 753 754 <group id="1d\_grid\_T" name="auto" description="ocean T grid variables" > } 755 <file id="floats" description="floats variables"> }\\ 756 <field ref="traj\_lon" name="floats\_longitude" freq\_op="86400" />} 757 <field ref="traj\_lat" name="floats\_latitude" freq\_op="86400" />} 758 <field ref="traj\_dep" name="floats\_depth" freq\_op="86400" />} 759 <field ref="traj\_temp" name="floats\_temperature" freq\_op="86400" />} 760 <field ref="traj\_salt" name="floats\_salinity" freq\_op="86400" />} 761 <field ref="traj\_dens" name="floats\_density" freq\_op="86400" />} 762 <field ref="traj\_group" name="floats\_group" freq\_op="86400" />} 763 </file>} 764 </group>} 765 766 \end{verbatim} 767 }}\end{alltt} 768 769 770 - if (\key{iomput}) is not used, a file called \np{trajec\_float.nc} will be created by IOIPSL library. 771 772 773 683 774 See also \href{http://stockage.univ-brest.fr/~grima/Ariane/}{here} the web site describing 684 775 the off-line use of this marvellous diagnostic tool. 776 777 778 % ------------------------------------------------------------------------------------------------------------- 779 % Harmonic analysis of tidal constituents 780 % ------------------------------------------------------------------------------------------------------------- 781 \section{Harmonic analysis of tidal constituents (\key{diaharm}) } 782 \label{DIA_diag_harm} 783 784 A module is available to compute the amplitude and phase for tidal waves. 785 This diagnostic is actived with \key{diaharm}. 786 787 %------------------------------------------namdia_harm---------------------------------------------------- 788 \namdisplay{namdia_harm} 789 %---------------------------------------------------------------------------------------------------------- 790 791 Concerning the on-line Harmonic analysis, some parameters are available in namelist: 792 793 - \texttt{nit000\_han} is the first time step used for harmonic analysis 794 795 - \texttt{nitend\_han} is the last time step used for harmonic analysis 796 797 - \texttt{nstep\_han} is the time step frequency for harmonic analysis 798 799 - \texttt{nb\_ana} is the number of harmonics to analyse 800 801 - \texttt{tname} is an array with names of tidal constituents to analyse 802 803 \texttt{nit000\_han} and \texttt{nitend\_han} must be between \texttt{nit000} and \texttt{nitend} of the simulation. 804 The restart capability is not implemented. 805 806 The Harmonic analysis solve this equation: 807 \begin{equation} 808 h_{i} - A_{0} + \sum^{nb\_ana}_{j=1}[A_{j}cos(\nu_{j}t_{j}-\phi_{j})] = e_{i} 809 \end{equation} 810 811 With $A_{j}$,$\nu_{j}$,$\phi_{j}$, the amplitude, frequency and phase for each wave and $e_{i}$ the error. 812 $h_{i}$ is the sea level for the time $t_{i}$ and $A_{0}$ is the mean sea level. \\ 813 We can rewrite this equation: 814 \begin{equation} 815 h_{i} - A_{0} + \sum^{nb\_ana}_{j=1}[C_{j}cos(\nu_{j}t_{j})+S_{j}sin(\nu_{j}t_{j})] = e_{i} 816 \end{equation} 817 with $A_{j}=\sqrt{C^{2}_{j}+S^{2}_{j}}$ et $\phi_{j}=arctan(S_{j}/C_{j})$. 818 819 We obtain in output $C_{j}$ and $S_{j}$ for each tidal wave. 820 821 % ------------------------------------------------------------------------------------------------------------- 822 % Sections transports 823 % ------------------------------------------------------------------------------------------------------------- 824 \section{Transports across sections (\key{diadct}) } 825 \label{DIA_diag_dct} 826 827 A module is available to compute the transport of volume, heat and salt through sections. This diagnostic 828 is actived with \key{diadct}. 829 830 Each section is defined by the coordinates of its 2 extremities. The pathways between them are contructed 831 using tools which can be found in \texttt{NEMOGCM/TOOLS/SECTIONS\_DIADCT} and are written in a binary file 832 \texttt{section\_ijglobal.diadct\_ORCA2\_LIM} which is later read in by NEMO to compute on-line transports. 833 834 The on-line transports module creates three output ascii files: 835 836 - \texttt{volume\_transport} for volume transports ( unit: $10^{6} m^{3} s^{-1}$ ) 837 838 - \texttt{heat\_transport} for heat transports ( unit: $10^{15} W $ ) 839 840 - \texttt{salt\_transport} for salt transports ( unit: $10^{9}g s^{-1}$ )\\ 841 842 843 Namelist parameters control how frequently the flows are summed and the time scales over which 844 they are averaged, as well as the level of output for debugging: 845 846 %------------------------------------------namdct---------------------------------------------------- 847 \namdisplay{namdct} 848 %------------------------------------------------------------------------------------------------------------- 849 850 \texttt{nn\_dct}: frequency of instantaneous transports computing 851 852 \texttt{nn\_dctwri}: frequency of writing ( mean of instantaneous transports ) 853 854 \texttt{nn\_debug}: debugging of the section 855 856 \subsubsection{ To create a binary file containing the pathway of each section } 857 858 In \texttt{NEMOGCM/TOOLS/SECTIONS\_DIADCT/run}, the file \texttt{ {list\_sections.ascii\_global}} 859 contains a list of all the sections that are to be computed (this list of sections is based on MERSEA project metrics). 860 861 Another file is available for the GYRE configuration (\texttt{ {list\_sections.ascii\_GYRE}}). 862 863 Each section is defined by: 864 865 \noindent \texttt{ long1 lat1 long2 lat2 nclass (ok/no)strpond (no)ice section\_name }\\ 866 with: 867 868 - \texttt{long1 lat1} , coordinates of the first extremity of the section; 869 870 - \texttt{long2 lat2} , coordinates of the second extremity of the section; 871 872 - \texttt{nclass} the number of bounds of your classes (e.g. 3 bounds for 2 classes); 873 874 - \texttt{okstrpond} to compute heat and salt transport, \texttt{nostrpond} if no; 875 876 - \texttt{ice} to compute surface and volume ice transports, \texttt{noice} if no. \\ 877 878 879 \noindent The results of the computing of transports, and the directions of positive 880 and negative flow do not depend on the order of the 2 extremities in this file.\\ 881 882 883 \noindent If nclass =/ 0,the next lines contain the class type and the nclass bounds: 884 885 \texttt{long1 lat1 long2 lat2 nclass (ok/no)strpond (no)ice section\_name} 886 887 \texttt{classtype} 888 889 \texttt{zbound1} 890 891 \texttt{zbound2} 892 893 \texttt{.} 894 895 \texttt{.} 896 897 \texttt{nclass-1} 898 899 \texttt{nclass} 900 901 \noindent where \texttt{classtype} can be: 902 903 - \texttt{zsal} for salinity classes 904 905 - \texttt{ztem} for temperature classes 906 907 - \texttt{zlay} for depth classes 908 909 - \texttt{zsigi} for insitu density classes 910 911 - \texttt{zsigp} for potential density classes \\ 912 913 914 The script \texttt{job.ksh} computes the pathway for each section and creates a binary file 915 \texttt{section\_ijglobal.diadct\_ORCA2\_LIM} which is read by NEMO. \\ 916 917 It is possible to use this tools for new configuations: \texttt{job.ksh} has to be updated 918 with the coordinates file name and path. \\ 919 920 921 Examples of two sections, the ACC\_Drake\_Passage with no classes, and the 922 ATL\_Cuba\_Florida with 4 temperature clases (5 class bounds), are shown: 923 924 \noindent \texttt{ -68. -54.5 -60. -64.7 00 okstrpond noice ACC\_Drake\_Passage} 925 926 \noindent \texttt{ -80.5 22.5 -80.5 25.5 05 nostrpond noice ATL\_Cuba\_Florida} 927 928 \noindent \texttt{ztem} 929 930 \noindent \texttt{-2.0} 931 932 \noindent \texttt{ 4.5} 933 934 \noindent \texttt{ 7.0} 935 936 \noindent \texttt{12.0} 937 938 \noindent \texttt{40.0} 939 940 941 \subsubsection{ To read the output files } 942 943 The output format is : 944 945 {\small\texttt{date, time-step number, section number, section name, section slope coefficient, class number, 946 class name, class bound 1 , classe bound2, transport\_direction1 , transport\_direction2, transport\_total}}\\ 947 948 949 For sections with classes, the first \texttt{nclass-1} lines correspond to the transport for each class 950 and the last line corresponds to the total transport summed over all classes. For sections with no classes, class number 951 \texttt{ 1 } corresponds to \texttt{ total class } and this class is called \texttt{N}, meaning \texttt{none}.\\ 952 953 954 \noindent \texttt{ transport\_direction1 } is the positive part of the transport ( \texttt{ > = 0 } ). 955 956 \noindent \texttt{ transport\_direction2 } is the negative part of the transport ( \texttt{ < = 0 } ).\\ 957 958 959 \noindent The \texttt{section slope coefficient} gives information about the significance of transports signs and direction:\\ 960 961 962 963 \begin{tabular}{|c|c|c|c|p{4cm}|} 964 \hline 965 section slope coefficient & section type & direction 1 & direction 2 & total transport \\ \hline 966 0. & horizontal & northward & southward & postive: northward \\ \hline 967 1000. & vertical & eastward & westward & postive: eastward \\ \hline 968 \texttt{=/0, =/ 1000.} & diagonal & eastward & westward & postive: eastward \\ \hline 969 \end{tabular} 970 971 685 972 686 973 % ------------------------------------------------------------------------------------------------------------- … … 726 1013 are removed from the sub-basins. Note also that the Arctic Ocean has been split 727 1014 into Atlantic and Pacific basins along the North fold line. } 728 \end{center} \end{figure} 1015 \end{center} \end{figure} 729 1016 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> 730 1017 … … 733 1020 (see Section \ref{MISC_steric} below for one of them). 734 1021 Activating those outputs requires to define the \key{diaar5} CPP key. 1022 \\ 1023 \\ 735 1024 736 1025 -
trunk/DOC/TexFiles/Chapters/Chap_DOM.tex
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r2376 r3294 81 81 82 82 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> 83 \begin{table}[!tb] \label{Tab_cell}83 \begin{table}[!tb] 84 84 \begin{center} \begin{tabular}{|p{46pt}|p{56pt}|p{56pt}|p{56pt}|} 85 85 \hline … … 93 93 fw & $i+1/2$ & $j+1/2$ & $k+1/2$ \\ \hline 94 94 \end{tabular} 95 \caption{ \label{Tab_cell} 95 \caption{ \label{Tab_cell} 96 96 Location of grid-points as a function of integer or integer and a half value of the column, 97 97 line or level. This indexing is only used for the writing of the semi-discrete equation. … … 123 123 the following discrete forms in the curvilinear $s$-coordinate system: 124 124 \begin{equation} \label{Eq_DOM_grad} 125 \nabla q\equiv \frac{1}{e_{1u} } \delta _{i+1/2 } [q] \;\, {\rm {\bf i}}126 + \frac{1}{e_{2v} } \delta _{j+1/2 } [q] \;\, {\rm {\bf j}}127 + \frac{1}{e_{3w}} \delta _{k+1/2} [q] \;\, {\rm {\bf k}}125 \nabla q\equiv \frac{1}{e_{1u} } \delta _{i+1/2 } [q] \;\,\mathbf{i} 126 + \frac{1}{e_{2v} } \delta _{j+1/2 } [q] \;\,\mathbf{j} 127 + \frac{1}{e_{3w}} \delta _{k+1/2} [q] \;\,\mathbf{k} 128 128 \end{equation} 129 129 \begin{multline} \label{Eq_DOM_lap} 130 \Delta q\equiv \frac{1}{e_{1t}\,e_{2t}\,e_{3t} } 130 \Delta q\equiv \frac{1}{e_{1t}\,e_{2t}\,e_{3t} } 131 131 \;\left( \delta_i \left[ \frac{e_{2u}\,e_{3u}} {e_{1u}} \;\delta_{i+1/2} [q] \right] 132 132 + \delta_j \left[ \frac{e_{1v}\,e_{3v}} {e_{2v}} \;\delta_{j+1/2} [q] \right] \; \right) \\ … … 139 139 \begin{eqnarray} \label{Eq_DOM_curl} 140 140 \nabla \times {\rm {\bf A}}\equiv & 141 \frac{1}{e_{2v}\,e_{3vw} } \ \left( \delta_{j +1/2} \left[e_{3w}\,a_3 \right] -\delta_{k+1/2} \left[e_{2v} \,a_2 \right] \right) &\ \ rm{\bfi} \\142 +& \frac{1}{e_{2u}\,e_{3uw}} \ \left( \delta_{k+1/2} \left[e_{1u}\,a_1 \right] -\delta_{i +1/2} \left[e_{3w}\,a_3 \right] \right) &\ \ rm{\bf j} \\143 +& \frac{1}{e_{1f} \,e_{2f} } \ \left( \delta_{i +1/2} \left[e_{2v}\,a_2 \right] -\delta_{j +1/2} \left[e_{1u}\,a_1 \right] \right) &\ \ rm{\bfk}141 \frac{1}{e_{2v}\,e_{3vw} } \ \left( \delta_{j +1/2} \left[e_{3w}\,a_3 \right] -\delta_{k+1/2} \left[e_{2v} \,a_2 \right] \right) &\ \mathbf{i} \\ 142 +& \frac{1}{e_{2u}\,e_{3uw}} \ \left( \delta_{k+1/2} \left[e_{1u}\,a_1 \right] -\delta_{i +1/2} \left[e_{3w}\,a_3 \right] \right) &\ \mathbf{j} \\ 143 +& \frac{1}{e_{1f} \,e_{2f} } \ \left( \delta_{i +1/2} \left[e_{2v}\,a_2 \right] -\delta_{j +1/2} \left[e_{1u}\,a_1 \right] \right) &\ \mathbf{k} 144 144 \end{eqnarray} 145 145 \begin{equation} \label{Eq_DOM_div} … … 819 819 \end{align*} 820 820 821 \gmcomment{ STEVEN: are the dots multiplications?}822 823 821 Note that \textit{wmask} is not defined as it is exactly equal to \textit{tmask} with 824 822 the numerical indexing used (\S~\ref{DOM_Num_Index}). Moreover, the … … 832 830 \gmcomment{ \colorbox{yellow}{Add one word on tricky trick !} mbathy in further modified in zdfbfr{\ldots}. } 833 831 %%% 832 833 % ================================================================ 834 % Domain: Initial State (dtatsd & istate) 835 % ================================================================ 836 \section [Domain: Initial State (\textit{istate and dtatsd})] 837 {Domain: Initial State \small{(\mdl{istate} and \mdl{dtatsd} modules)} } 838 \label{DTA_tsd} 839 %-----------------------------------------namtsd------------------------------------------- 840 \namdisplay{namtsd} 841 %------------------------------------------------------------------------------------------ 842 843 By default, the ocean start from rest (the velocity field is set to zero) and the initialization of 844 temperature and salinity fields is controlled through the \np{ln\_tsd\_ini} namelist parameter. 845 \begin{description} 846 \item[ln\_tsd\_init = .true.] use a T and S input files that can be given on the model grid itself or 847 on their native input data grid. In the latter case, the data will be interpolated on-the-fly both in the 848 horizontal and the vertical to the model grid (see \S~\ref{SBC_iof}). The information relative to the 849 input files are given in the \np{sn\_tem} and \np{sn\_sal} structures. 850 The computation is done in the \mdl{dtatsd} module. 851 \item[ln\_tsd\_init = .false.] use constant salinity value of 35.5 psu and an analytical profile of temperature 852 (typical of the tropical ocean), see \rou{istate\_t\_s} subroutine called from \mdl{istate} module. 853 \end{description} -
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r2541 r3294 189 189 the relative vorticity term and horizontal kinetic energy for the planetary vorticity 190 190 term (MIX scheme) ; or conserving both the potential enstrophy of horizontally non-divergent 191 flow and horizontal kinetic energy (ENE scheme) (see Appendix~\ref{Apdx_C_vor_zad}). 191 flow and horizontal kinetic energy (EEN scheme) (see Appendix~\ref{Apdx_C_vor_zad}). In the 192 case of ENS, ENE or MIX schemes the land sea mask may be slightly modified to ensure the 193 consistency of vorticity term with analytical equations (\textit{ln\_dynvor\_con}=true). 192 194 The vorticity terms are all computed in dedicated routines that can be found in 193 195 the \mdl{dynvor} module. … … 605 607 Pressure gradient formulations in an $s$-coordinate have been the subject of a vast 606 608 number of papers ($e.g.$, \citet{Song1998, Shchepetkin_McWilliams_OM05}). 607 A number of different pressure gradient options are coded, but they are not yet fully 608 documented or tested. 609 610 $\bullet$ Traditional coding (see for example \citet{Madec_al_JPO96}: (\np{ln\_dynhpg\_sco}=true, 611 \np{ln\_dynhpg\_hel}=true) 609 A number of different pressure gradient options are coded but the ROMS-like, density Jacobian with 610 cubic polynomial method is currently disabled whilst known bugs are under investigation. 611 612 $\bullet$ Traditional coding (see for example \citet{Madec_al_JPO96}: (\np{ln\_dynhpg\_sco}=true) 612 613 \begin{equation} \label{Eq_dynhpg_sco} 613 614 \left\{ \begin{aligned} … … 622 623 \eqref{Eq_dynhpg_zco_surf} - \eqref{Eq_dynhpg_zco}, and $z_T$ is the depth of 623 624 the $T$-point evaluated from the sum of the vertical scale factors at the $w$-point 624 ($e_{3w}$). The version \np{ln\_dynhpg\_hel}=true has been added by Aike 625 Beckmann and involves a redefinition of the relative position of $T$-points relative 626 to $w$-points. 627 628 $\bullet$ Weighted density Jacobian (WDJ) \citep{Song1998} (\np{ln\_dynhpg\_wdj}=true) 625 ($e_{3w}$). 626 627 $\bullet$ Pressure Jacobian scheme (prj) (a research paper in preparation) (\np{ln\_dynhpg\_prj}=true) 629 628 630 629 $\bullet$ Density Jacobian with cubic polynomial scheme (DJC) \citep{Shchepetkin_McWilliams_OM05} 631 (\np{ln\_dynhpg\_djc}=true) 632 633 $\bullet$ Rotated axes scheme (rot) \citep{Thiem_Berntsen_OM06} (\np{ln\_dynhpg\_rot}=true) 634 635 Note that expression \eqref{Eq_dynhpg_sco} is used when the variable volume 636 formulation is activated (\key{vvl}) because in that case, even with a flat bottom, 637 the coordinate surfaces are not horizontal but follow the free surface 638 \citep{Levier2007}. The other pressure gradient options are not yet available. 630 (\np{ln\_dynhpg\_djc}=true) (currently disabled; under development) 631 632 Note that expression \eqref{Eq_dynhpg_sco} is commonly used when the variable volume formulation is 633 activated (\key{vvl}) because in that case, even with a flat bottom, the coordinate surfaces are not 634 horizontal but follow the free surface \citep{Levier2007}. The pressure jacobian scheme 635 (\np{ln\_dynhpg\_prj}=true) is available as an improved option to \np{ln\_dynhpg\_sco}=true when 636 \key{vvl} is active. The pressure Jacobian scheme uses a constrained cubic spline to reconstruct 637 the density profile across the water column. This method maintains the monotonicity between the 638 density nodes The pressure can be calculated by analytical integration of the density profile and a 639 pressure Jacobian method is used to solve the horizontal pressure gradient. This method can provide 640 a more accurate calculation of the horizontal pressure gradient than the standard scheme. 639 641 640 642 %-------------------------------------------------------------------------------------------------------------- … … 1162 1164 1163 1165 % ================================================================ 1166 % Neptune effect 1167 % ================================================================ 1168 \section [Neptune effect (\textit{dynnept})] 1169 {Neptune effect (\mdl{dynnept})} 1170 \label{DYN_nept} 1171 1172 The "Neptune effect" (thus named in \citep{HollowayOM86}) is a 1173 parameterisation of the potentially large effect of topographic form stress 1174 (caused by eddies) in driving the ocean circulation. Originally developed for 1175 low-resolution models, in which it was applied via a Laplacian (second-order) 1176 diffusion-like term in the momentum equation, it can also be applied in eddy 1177 permitting or resolving models, in which a more scale-selective bilaplacian 1178 (fourth-order) implementation is preferred. This mechanism has a 1179 significant effect on boundary currents (including undercurrents), and the 1180 upwelling of deep water near continental shelves. 1181 1182 The theoretical basis for the method can be found in 1183 \citep{HollowayJPO92}, including the explanation of why form stress is not 1184 necessarily a drag force, but may actually drive the flow. 1185 \citep{HollowayJPO94} demonstrate the effects of the parameterisation in 1186 the GFDL-MOM model, at a horizontal resolution of about 1.8 degrees. 1187 \citep{HollowayOM08} demonstrate the biharmonic version of the 1188 parameterisation in a global run of the POP model, with an average horizontal 1189 grid spacing of about 32km. 1190 1191 The NEMO implementation is a simplified form of that supplied by 1192 Greg Holloway, the testing of which was described in \citep{HollowayJGR09}. 1193 The major simplification is that a time invariant Neptune velocity 1194 field is assumed. This is computed only once, during start-up, and 1195 made available to the rest of the code via a module. Vertical 1196 diffusive terms are also ignored, and the model topography itself 1197 is used, rather than a separate topographic dataset as in 1198 \citep{HollowayOM08}. This implementation is only in the iso-level 1199 formulation, as is the case anyway for the bilaplacian operator. 1200 1201 The velocity field is derived from a transport stream function given by: 1202 1203 \begin{equation} \label{Eq_dynnept_sf} 1204 \psi = -fL^2H 1205 \end{equation} 1206 1207 where $L$ is a latitude-dependant length scale given by: 1208 1209 \begin{equation} \label{Eq_dynnept_ls} 1210 L = l_1 + (l_2 -l_1)\left ( {1 + \cos 2\phi \over 2 } \right ) 1211 \end{equation} 1212 1213 where $\phi$ is latitude and $l_1$ and $l_2$ are polar and equatorial length scales respectively. 1214 Neptune velocity components, $u^*$, $v^*$ are derived from the stremfunction as: 1215 1216 \begin{equation} \label{Eq_dynnept_vel} 1217 u^* = -{1\over H} {\partial \psi \over \partial y}\ \ \ ,\ \ \ v^* = {1\over H} {\partial \psi \over \partial x} 1218 \end{equation} 1219 1220 \smallskip 1221 %----------------------------------------------namdom---------------------------------------------------- 1222 \namdisplay{namdyn_nept} 1223 %-------------------------------------------------------------------------------------------------------- 1224 \smallskip 1225 1226 The Neptune effect is enabled when \np{ln\_neptsimp}=true (default=false). 1227 \np{ln\_smooth\_neptvel} controls whether a scale-selective smoothing is applied 1228 to the Neptune effect flow field (default=false) (this smoothing method is as 1229 used by Holloway). \np{rn\_tslse} and \np{rn\_tslsp} are the equatorial and 1230 polar values respectively of the length-scale parameter $L$ used in determining 1231 the Neptune stream function \eqref{Eq_dynnept_sf} and \eqref{Eq_dynnept_ls}. 1232 Values at intermediate latitudes are given by a cosine fit, mimicking the 1233 variation of the deformation radius with latitude. The default values of 12km 1234 and 3km are those given in \citep{HollowayJPO94}, appropriate for a coarse 1235 resolution model. The finer resolution study of \citep{HollowayOM08} increased 1236 the values of L by a factor of $\sqrt 2$ to 17km and 4.2km, thus doubling the 1237 stream function for a given topography. 1238 1239 The simple formulation for ($u^*$, $v^*$) can give unacceptably large velocities 1240 in shallow water, and \citep{HollowayOM08} add an offset to the depth in the 1241 denominator to control this problem. In this implementation we offer instead (at 1242 the suggestion of G. Madec) the option of ramping down the Neptune flow field to 1243 zero over a finite depth range. The switch \np{ln\_neptramp} activates this 1244 option (default=false), in which case velocities at depths greater than 1245 \np{rn\_htrmax} are unaltered, but ramp down linearly with depth to zero at a 1246 depth of \np{rn\_htrmin} (and shallower). 1247 1248 % ================================================================ -
trunk/DOC/TexFiles/Chapters/Chap_LBC.tex
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r3230 r3294 742 742 743 743 %-----------------------------------------nambdy-------------------------------------------- 744 %- cn_mask = '' ! name of mask file (if ln_bdy_mask=.TRUE.)745 %- cn_dta_frs_T = 'bdydata_grid_T.nc' ! name of data file (T-points)746 %- cn_dta_frs_U = 'bdydata_grid_U.nc' ! name of data file (U-points)747 %- cn_dta_frs_V = 'bdydata_grid_V.nc' ! name of data file (V-points)748 %- cn_dta_fla_T = 'bdydata_bt_grid_T.nc' ! name of data file for Flather condition (T-points)749 %- cn_dta_fla_U = 'bdydata_bt_grid_U.nc' ! name of data file for Flather condition (U-points)750 %- cn_dta_fla_V = 'bdydata_bt_grid_V.nc' ! name of data file for Flather condition (V-points)751 %- ln_clim = .false. ! contain 1 (T) or 12 (F) time dumps and be cyclic752 %- ln_vol = .true. ! total volume correction (see volbdy parameter)753 %- ln_mask = .false. ! boundary mask from filbdy_mask (T) or boundaries are on edges of domain (F)754 %- ln_tides = .true. ! Apply tidal harmonic forcing with Flather condition755 %- ln_dyn_fla = .true. ! Apply Flather condition to velocities756 %- ln_tra_frs = .false. ! Apply FRS condition to temperature and salinity757 %- ln_dyn_frs = .false. ! Apply FRS condition to velocities758 %- nn_rimwidth = 9 ! width of the relaxation zone759 %- nn_dtactl = 1 ! = 0, bdy data are equal to the initial state760 %- ! = 1, bdy data are read in 'bdydata .nc' files761 %- nn_volctl = 0 ! = 0, the total water flux across open boundaries is zero762 %- ! = 1, the total volume of the system is conserved763 744 \namdisplay{nambdy} 745 %----------------------------------------------------------------------------------------------- 746 %-----------------------------------------nambdy_index-------------------------------------------- 747 \namdisplay{nambdy_index} 748 %----------------------------------------------------------------------------------------------- 749 %-----------------------------------------nambdy_dta-------------------------------------------- 750 \namdisplay{nambdy_dta} 751 %----------------------------------------------------------------------------------------------- 752 %-----------------------------------------nambdy_dta-------------------------------------------- 753 \namdisplay{nambdy_dta2} 764 754 %----------------------------------------------------------------------------------------------- 765 755 … … 774 764 The BDY module was modelled on the OBC module and shares many features 775 765 and a similar coding structure \citep{Chanut2005}. 766 767 The BDY module is completely rewritten at NEMO 3.4 and there is a new 768 set of namelists. Boundary data files used with earlier versions of 769 NEMO may need to be re-ordered to work with this version. See the 770 section on the Input Boundary Data Files for details. 771 772 %---------------------------------------------- 773 \subsection{The namelists} 774 \label{BDY_namelist} 775 776 It is possible to define more than one boundary ``set'' and apply 777 different boundary conditions to each set. The number of boundary 778 sets is defined by \np{nb\_bdy}. Each boundary set may be defined 779 as a set of straight line segments in a namelist 780 (\np{ln\_coords\_file}=.false.) or read in from a file 781 (\np{ln\_coords\_file}=.true.). If the set is defined in a namelist, 782 then the namelists nambdy\_index must be included separately, one for 783 each set. If the set is defined by a file, then a 784 ``coordinates.bdy.nc'' file must be provided. The coordinates.bdy file 785 is analagous to the usual NEMO ``coordinates.nc'' file. In the example 786 above, there are two boundary sets, the first of which is defined via 787 a file and the second is defined in a namelist. For more details of 788 the definition of the boundary geometry see section 789 \ref{BDY_geometry}. 790 791 For each boundary set a boundary 792 condition has to be chosen for the barotropic solution (``u2d'': 793 sea-surface height and barotropic velocities), for the baroclinic 794 velocities (``u3d''), and for the active tracers\footnote{The BDY 795 module does not deal with passive tracers at this version} 796 (``tra''). For each set of variables there is a choice of algorithm 797 and a choice for the data, eg. for the active tracers the algorithm is 798 set by \np{nn\_tra} and the choice of data is set by 799 \np{nn\_tra\_dta}. 800 801 The choice of algorithm is currently as follows: 802 803 \mbox{} 804 805 \begin{itemize} 806 \item[0.] No boundary condition applied. So the solution will ``see'' 807 the land points around the edge of the edge of the domain. 808 \item[1.] Flow Relaxation Scheme (FRS) available for all variables. 809 \item[2.] Flather radiation scheme for the barotropic variables. The 810 Flather scheme is not compatible with the filtered free surface 811 ({\it dynspg\_ts}). 812 \end{itemize} 813 814 \mbox{} 815 816 The main choice for the boundary data is 817 to use initial conditions as boundary data (\np{nn\_tra\_dta}=0) or to 818 use external data from a file (\np{nn\_tra\_dta}=1). For the 819 barotropic solution there is also the option to use tidal 820 harmonic forcing either by itself or in addition to other external 821 data. 822 823 If external boundary data is required then the nambdy\_dta namelist 824 must be defined. One nambdy\_dta namelist is required for each boundary 825 set in the order in which the boundary sets are defined in nambdy. In 826 the example given, two boundary sets have been defined and so there 827 are two nambdy\_dta namelists. The boundary data is read in using the 828 fldread module, so the nambdy\_dta namelist is in the format required 829 for fldread. For each variable required, the filename, the frequency 830 of the files and the frequency of the data in the files is given. Also 831 whether or not time-interpolation is required and whether the data is 832 climatological (time-cyclic) data. Note that on-the-fly spatial 833 interpolation of boundary data is not available at this version. 834 835 In the example namelists given, two boundary sets are defined. The 836 first set is defined via a file and applies FRS conditions to 837 temperature and salinity and Flather conditions to the barotropic 838 variables. External data is provided in daily files (from a 839 large-scale model). Tidal harmonic forcing is also used. The second 840 set is defined in a namelist. FRS conditions are applied on 841 temperature and salinity and climatological data is read from external 842 files. 776 843 777 844 %---------------------------------------------- … … 832 899 Note that the sea-surface height gradient in \eqref{Eq_bdy_fla1} 833 900 is a spatial gradient across the model boundary, so that $\eta_{e}$ is 834 defined on the $T$ points with $nbrdta=1$ and $\eta$ is defined on the 835 $T$ points with $nbrdta=2$. $U$ and $U_{e}$ are defined on the $U$ or 836 $V$ points with $nbrdta=1$, $i.e.$ between the two $T$ grid points. 837 838 %---------------------------------------------- 839 \subsection{Choice of schemes} 840 \label{BDY_choice_of_schemes} 841 842 The Flow Relaxation Scheme may be applied separately to the 843 temperature and salinity (\np{ln\_tra\_frs} = true) and 844 the velocity fields (\np{ln\_dyn\_frs} = true). Flather 845 radiation conditions may be applied using externally defined 846 barotropic velocities and sea-surface height (\np{ln\_dyn\_fla} = true) 847 or using tidal harmonics fields (\np{ln\_tides} = true) 848 or both. FRS and Flather conditions may be applied simultaneously. 849 A typical configuration where all possible conditions might be used is a tidal, 850 shelf-seas model, where the barotropic boundary conditions are fixed 851 with the Flather scheme using tidal harmonics and possibly output 852 from a large-scale model, and FRS conditions are applied to the tracers 853 and baroclinic velocity fields, using fields from a large-scale model. 854 855 Note that FRS conditions will work with the filtered 856 (\key{dynspg\_flt}) or time-split (\key{dynspg\_ts}) solutions for the 857 surface pressure gradient. The Flather condition will only work for 858 the time-split solution (\key{dynspg\_ts}). FRS conditions are applied 859 at the end of the main model time step. Flather conditions are applied 860 during the barotropic subcycle in the time-split solution. 901 defined on the $T$ points with $nbr=1$ and $\eta$ is defined on the 902 $T$ points with $nbr=2$. $U$ and $U_{e}$ are defined on the $U$ or 903 $V$ points with $nbr=1$, $i.e.$ between the two $T$ grid points. 861 904 862 905 %---------------------------------------------- … … 864 907 \label{BDY_geometry} 865 908 866 The definition of the open boundary is completely flexible. An example 867 is shown in Fig.~\ref{Fig_LBC_bdy_geom}. The boundary zone is 868 defined by a series of index arrays read in from the input boundary 869 data files: $nbidta$, $nbjdta$, and $nbrdta$. The first two of these 870 define the global $(i,j)$ indices of each point in the boundary zone 871 and the $nbrdta$ array defines the discrete distance from the boundary 872 with $nbrdta=1$ meaning that the point is next to the edge of the 873 model domain and $nbrdta>1$ showing that the point is increasingly 874 further away from the edge of the model domain. These arrays are 875 defined separately for each of the $T$, $U$ and $V$ grids, but the 876 relationship between the points is assumed to be as in Fig. 877 \ref{Fig_LBC_bdy_geom} with the $T$ points forming the outermost row 878 of the boundary and the first row of velocities normal to the boundary 879 being inside the first row of $T$ points. The order in which the 880 points are defined is unimportant. 909 Each open boundary set is defined as a list of points. The information 910 is stored in the arrays $nbi$, $nbj$, and $nbr$ in the $idx\_bdy$ 911 structure. The $nbi$ and $nbj$ arrays 912 define the local $(i,j)$ indices of each point in the boundary zone 913 and the $nbr$ array defines the discrete distance from the boundary 914 with $nbr=1$ meaning that the point is next to the edge of the 915 model domain and $nbr>1$ showing that the point is increasingly 916 further away from the edge of the model domain. A set of $nbi$, $nbj$, 917 and $nbr$ arrays is defined for each of the $T$, $U$ and $V$ 918 grids. Figure \ref{Fig_LBC_bdy_geom} shows an example of an irregular 919 boundary. 920 921 The boundary geometry for each set may be defined in a namelist 922 nambdy\_index or by reading in a ``coordinates.bdy.nc'' file. The 923 nambdy\_index namelist defines a series of straight-line segments for 924 north, east, south and west boundaries. For the northern boundary, 925 \np{nbdysegn} gives the number of segments, \np{jpjnob} gives the $j$ 926 index for each segment and \np{jpindt} and \np{jpinft} give the start 927 and end $i$ indices for each segment with similar for the other 928 boundaries. These segments define a list of $T$ grid points along the 929 outermost row of the boundary ($nbr\,=\, 1$). The code deduces the $U$ and 930 $V$ points and also the points for $nbr\,>\, 1$ if 931 $nn\_rimwidth\,>\,1$. 932 933 The boundary geometry may also be defined from a 934 ``coordinates.bdy.nc'' file. Figure \ref{Fig_LBC_nc_header} 935 gives an example of the header information from such a file. The file 936 should contain the index arrays for each of the $T$, $U$ and $V$ 937 grids. The arrays must be in order of increasing $nbr$. Note that the 938 $nbi$, $nbj$ values in the file are global values and are converted to 939 local values in the code. Typically this file will be used to generate 940 external boundary data via interpolation and so will also contain the 941 latitudes and longitudes of each point as shown. However, this is not 942 necessary to run the model. 943 944 For some choices of irregular boundary the model domain may contain 945 areas of ocean which are not part of the computational domain. For 946 example if an open boundary is defined along an isobath, say at the 947 shelf break, then the areas of ocean outside of this boundary will 948 need to be masked out. This can be done by reading a mask file defined 949 as \np{cn\_mask\_file} in the nam\_bdy namelist. Only one mask file is 950 used even if multiple boundary sets are defined. 881 951 882 952 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> … … 892 962 \label{BDY_data} 893 963 894 The input data files for the FRS conditions are defined in the 895 namelist as \np{cn\_dta\_frs\_T}, \np{cn\_dta\_frs\_U}, 896 \np{cn\_dta\_frs\_V}. The input data files for the Flather conditions 897 are defined in the namelist as \np{cn\_dta\_fla\_T}, 898 \np{cn\_dta\_fla\_U}, \np{cn\_dta\_fla\_V}. 899 900 The netcdf header of a typical input data file is shown in Fig.~\ref{Fig_LBC_nc_header}. 901 The file contains the index arrays which define the boundary geometry 902 as noted above and the data arrays for each field. 903 The data arrays are dimensioned on: a time dimension; $xb$ 904 which is the index of the boundary data point in the horizontal; 905 and $yb$ which is a degenerate dimension of 1 to enable 906 the file to be read by the standard NEMO I/O routines. The 3D fields 907 also have a depth dimension. 908 909 If \np{ln\_clim} is set to \textit{false}, the model expects the 910 units of the time axis to have the form shown in 911 Fig.~\ref{Fig_LBC_nc_header}, $i.e.$ {\it ``seconds since yyyy-mm-dd 912 hh:mm:ss''} The fields are then linearly interpolated to the model 913 time at each timestep. Note that for this option, the time axis of the 914 input files must completely span the time period of the model 915 integration. If \np{ln\_clim} is set to \textit{true} (climatological 916 boundary forcing), the model will expect either a single set of annual 917 mean fields (constant boundary forcing) or 12 sets of monthly mean 918 fields in the input files. 919 920 As in the OBC module there is an option to use initial conditions as 921 boundary conditions. This is chosen by setting 922 \np{nn\_dtactl}~=~0. However, since the model defines the boundary 923 geometry by reading the boundary index arrays from the input files, 924 it is still necessary to provide a set of input files in this 925 case. They need only contain the boundary index arrays, $nbidta$, 926 \textit{nbjdta}, \textit{nbrdta}. 964 The data files contain the data arrays 965 in the order in which the points are defined in the $nbi$ and $nbj$ 966 arrays. The data arrays are dimensioned on: a time dimension; 967 $xb$ which is the index of the boundary data point in the horizontal; 968 and $yb$ which is a degenerate dimension of 1 to enable the file to be 969 read by the standard NEMO I/O routines. The 3D fields also have a 970 depth dimension. 971 972 At Version 3.4 there are new restrictions on the order in which the 973 boundary points are defined (and therefore restrictions on the order 974 of the data in the file). In particular: 975 976 \mbox{} 977 978 \begin{enumerate} 979 \item The data points must be in order of increasing $nbr$, ie. all 980 the $nbr=1$ points, then all the $nbr=2$ points etc. 981 \item All the data for a particular boundary set must be in the same 982 order. (Prior to 3.4 it was possible to define barotropic data in a 983 different order to the data for tracers and baroclinic velocities). 984 \end{enumerate} 985 986 \mbox{} 987 988 These restrictions mean that data files used with previous versions of 989 the model may not work with version 3.4. A fortran utility 990 {\it bdy\_reorder} exists in the TOOLS directory which will re-order the 991 data in old BDY data files. 927 992 928 993 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> … … 930 995 \includegraphics[width=1.0\textwidth]{./TexFiles/Figures/Fig_LBC_nc_header.pdf} 931 996 \caption { \label{Fig_LBC_nc_header} 932 Example of header of netcdf input data file for BDY}997 Example of the header for a coordinates.bdy.nc file} 933 998 \end{center} \end{figure} 934 999 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> … … 940 1005 There is an option to force the total volume in the regional model to be constant, 941 1006 similar to the option in the OBC module. This is controlled by the \np{nn\_volctl} 942 parameter in the namelist. A value of \np{nn\_volctl}~=~0 indicates that this option is not used.1007 parameter in the namelist. A value of \np{nn\_volctl}~=~0 indicates that this option is not used. 943 1008 If \np{nn\_volctl}~=~1 then a correction is applied to the normal velocities 944 1009 around the boundary at each timestep to ensure that the integrated volume flow … … 947 1012 flux across the surface and the correction velocity corrects for this as well. 948 1013 949 1014 If more than one boundary set is used then volume correction is 1015 applied to all boundaries at once. 1016 1017 \newpage 950 1018 %---------------------------------------------- 951 1019 \subsection{Tidal harmonic forcing} 952 1020 \label{BDY_tides} 953 1021 1022 %-----------------------------------------nambdy_tide-------------------------------------------- 1023 \namdisplay{nambdy_tide} 1024 %----------------------------------------------------------------------------------------------- 1025 954 1026 To be written.... 955 1027 -
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r2376 r3294 21 21 and for tracers only, eddy induced advection on tracers). These three aspects 22 22 of the lateral diffusion are set through namelist parameters and CPP keys 23 (see the \textit{nam\_traldf} and \textit{nam\_dynldf} below). 23 (see the \textit{nam\_traldf} and \textit{nam\_dynldf} below). Note 24 that this chapter describes the default implementation of iso-neutral 25 tracer mixing, and Griffies's implementation, which is used if 26 \np{traldf\_grif}=true, is described in Appdx\ref{sec:triad} 24 27 25 28 %-----------------------------------nam_traldf - nam_dynldf-------------------------------------------- … … 128 131 $\ $\newline % force a new ligne 129 132 130 A space variation in the eddy coefficient appeals several remarks:133 The following points are relevant when the eddy coefficient varies spatially: 131 134 132 135 (1) the momentum diffusion operator acting along model level surfaces is 133 136 written in terms of curl and divergent components of the horizontal current 134 (see \S\ref{PE_ldf}). Although the eddy coefficient c anbe set to different values135 in these two terms, this option is not available.137 (see \S\ref{PE_ldf}). Although the eddy coefficient could be set to different values 138 in these two terms, this option is not currently available. 136 139 137 140 (2) with an horizontally varying viscosity, the quadratic integral constraints … … 220 223 and either \np{ln\_traldf\_hor}=True or \np{ln\_dynldf\_hor}=True. 221 224 222 \subsection{ slopes for tracer iso-neutral mixing}225 \subsection{Slopes for tracer iso-neutral mixing}\label{LDF_slp_iso} 223 226 In iso-neutral mixing $r_1$ and $r_2$ are the slopes between the iso-neutral 224 227 and computational surfaces. Their formulation does not depend on the vertical … … 275 278 276 279 \item[$s$- or hybrid $s$-$z$- coordinate : ] in the current release of \NEMO, 277 there is no specific treatment for iso-neutral mixing in the $s$-coordinate. 280 iso-neutral mixing is only employed for $s$-coordinates if the 281 Griffies scheme is used (\np{traldf\_grif}=true; see Appdx \ref{sec:triad}). 278 282 In other words, iso-neutral mixing will only be accurately represented with a 279 283 linear equation of state (\np{nn\_eos}=1 or 2). In the case of a "true" equation … … 332 336 \end{description} 333 337 334 This implementation is a rather old one. It is similar to the one proposed 335 by Cox [1987], except for the background horizontal diffusion. Indeed, 336 the Cox implementation of isopycnal diffusion in GFDL-type models requires 337 a minimum background horizontal diffusion for numerical stability reasons. 338 To overcome this problem, several techniques have been proposed in which 339 the numerical schemes of the ocean model are modified \citep{Weaver_Eby_JPO97, 340 Griffies_al_JPO98}. Here, another strategy has been chosen \citep{Lazar_PhD97}: 341 a local filtering of the iso-neutral slopes (made on 9 grid-points) prevents 342 the development of grid point noise generated by the iso-neutral diffusion 343 operator (Fig.~\ref{Fig_LDF_ZDF1}). This allows an iso-neutral diffusion scheme 344 without additional background horizontal mixing. This technique can be viewed 345 as a diffusion operator that acts along large-scale (2~$\Delta$x) 346 \gmcomment{2deltax doesnt seem very large scale} 347 iso-neutral surfaces. The diapycnal diffusion required for numerical stability is 348 thus minimized and its net effect on the flow is quite small when compared to 349 the effect of an horizontal background mixing. 338 This implementation is a rather old one. It is similar to the one 339 proposed by Cox [1987], except for the background horizontal 340 diffusion. Indeed, the Cox implementation of isopycnal diffusion in 341 GFDL-type models requires a minimum background horizontal diffusion 342 for numerical stability reasons. To overcome this problem, several 343 techniques have been proposed in which the numerical schemes of the 344 ocean model are modified \citep{Weaver_Eby_JPO97, 345 Griffies_al_JPO98}. Griffies's scheme is now available in \NEMO if 346 \np{traldf\_grif\_iso} is set true; see Appdx \ref{sec:triad}. Here, 347 another strategy is presented \citep{Lazar_PhD97}: a local 348 filtering of the iso-neutral slopes (made on 9 grid-points) prevents 349 the development of grid point noise generated by the iso-neutral 350 diffusion operator (Fig.~\ref{Fig_LDF_ZDF1}). This allows an 351 iso-neutral diffusion scheme without additional background horizontal 352 mixing. This technique can be viewed as a diffusion operator that acts 353 along large-scale (2~$\Delta$x) \gmcomment{2deltax doesnt seem very 354 large scale} iso-neutral surfaces. The diapycnal diffusion required 355 for numerical stability is thus minimized and its net effect on the 356 flow is quite small when compared to the effect of an horizontal 357 background mixing. 350 358 351 359 Nevertheless, this iso-neutral operator does not ensure that variance cannot increase, … … 369 377 370 378 371 In addition and also for numerical stability reasons \citep{Cox1987, Griffies_Bk04},372 the slopes are bounded by $1/100$ everywhere. This limit is decreasing linearly373 to zero fom $70$ meters depth and the surface (the fact that the eddies "feel" the374 surface motivates this flattening of isopycnals near the surface).379 % In addition and also for numerical stability reasons \citep{Cox1987, Griffies_Bk04}, 380 % the slopes are bounded by $1/100$ everywhere. This limit is decreasing linearly 381 % to zero fom $70$ meters depth and the surface (the fact that the eddies "feel" the 382 % surface motivates this flattening of isopycnals near the surface). 375 383 376 384 For numerical stability reasons \citep{Cox1987, Griffies_Bk04}, the slopes must also -
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r2541 r3294 253 253 Note this implementation may be sensitive to the optimization level. 254 254 255 \subsection{MPP scalability} 256 \label{MISC_mppsca} 257 258 The default method of communicating values across the north-fold in distributed memory applications 259 (\key{mpp\_mpi}) uses a \textsc{MPI\_ALLGATHER} function to exchange values from each processing 260 region in the northern row with every other processing region in the northern row. This enables a 261 global width array containing the top 4 rows to be collated on every northern row processor and then 262 folded with a simple algorithm. Although conceptually simple, this "All to All" communication will 263 hamper performance scalability for large numbers of northern row processors. From version 3.4 264 onwards an alternative method is available which only performs direct "Peer to Peer" communications 265 between each processor and its immediate "neighbours" across the fold line. This is achieved by 266 using the default \textsc{MPI\_ALLGATHER} method during initialisation to help identify the "active" 267 neighbours. Stored lists of these neighbours are then used in all subsequent north-fold exchanges to 268 restrict exchanges to those between associated regions. The collated global width array for each 269 region is thus only partially filled but is guaranteed to be set at all the locations actually 270 required by each individual for the fold operation. This alternative method should give identical 271 results to the default \textsc{ALLGATHER} method and is recommended for large values of \np{jpni}. 272 The new method is activated by setting \np{ln\_nnogather} to be true ({\bf nammpp}). The 273 reproducibility of results using the two methods should be confirmed for each new, non-reference 274 configuration. 255 275 256 276 % ================================================================ -
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r2376 r3294 1094 1094 % Lateral Diffusive and Viscous Operators Formulation 1095 1095 % ------------------------------------------------------------------------------------------------------------- 1096 \subsection{ Lateral Diffusive and Viscous Operators Formulation}1096 \subsection{Formulation of the Lateral Diffusive and Viscous Operators} 1097 1097 \label{PE_ldf} 1098 1098 … … 1134 1134 1135 1135 In eddy-resolving configurations, a second order operator can be used, but 1136 usually a more scale selective one (biharmonic operator)is preferred as the1136 usually the more scale selective biharmonic operator is preferred as the 1137 1137 grid-spacing is usually not small enough compared to the scale of the 1138 1138 eddies. The role devoted to the subgrid-scale physics is to dissipate the 1139 energy that cascades toward the grid scale and thus ensuresthe stability of1140 the model while not interfering with the solved mesoscale activity. Another approach1139 energy that cascades toward the grid scale and thus to ensure the stability of 1140 the model while not interfering with the resolved mesoscale activity. Another approach 1141 1141 is becoming more and more popular: instead of specifying explicitly a sub-grid scale 1142 1142 term in the momentum and tracer time evolution equations, one uses a advective 1143 1143 scheme which is diffusive enough to maintain the model stability. It must be emphasised 1144 that then, all the sub-grid scale physics is in this case includein the formulation of the1144 that then, all the sub-grid scale physics is included in the formulation of the 1145 1145 advection scheme. 1146 1146 1147 All these parameterisations of subgrid scale physics presentadvantages and1147 All these parameterisations of subgrid scale physics have advantages and 1148 1148 drawbacks. There are not all available in \NEMO. In the $z$-coordinate 1149 1149 formulation, five options are offered for active tracers (temperature and … … 1157 1157 operator acting along $s-$surfaces (see \S\ref{LDF}). 1158 1158 1159 \subsubsection{ lateral second order tracer diffusive operator}1159 \subsubsection{Lateral second order tracer diffusive operator} 1160 1160 1161 1161 The lateral second order tracer diffusive operator is defined by (see Appendix~\ref{Apdx_B}): … … 1186 1186 1187 1187 For \textit{isoneutral} diffusion $r_1$ and $r_2$ are the slopes between the isoneutral 1188 and computational surfaces. Therefore, they have a same expression in $z$- and $s$-coordinates: 1188 and computational surfaces. Therefore, they are different quantities, 1189 but have similar expressions in $z$- and $s$-coordinates. In $z$-coordinates: 1189 1190 \begin{equation} \label{Eq_PE_iso_slopes} 1190 1191 r_1 =\frac{e_3 }{e_1 } \left( {\frac{\partial \rho }{\partial i}} \right) 1191 1192 \left( {\frac{\partial \rho }{\partial k}} \right)^{-1} \ , \quad 1192 1193 r_1 =\frac{e_3 }{e_1 } \left( {\frac{\partial \rho }{\partial i}} \right) 1193 \left( {\frac{\partial \rho }{\partial k}} \right)^{-1} 1194 \end{equation} 1195 1196 When the \textit{Eddy Induced Velocity} parametrisation (eiv) \citep{Gent1990} is used, 1194 \left( {\frac{\partial \rho }{\partial k}} \right)^{-1}, 1195 \end{equation} 1196 while in $s$-coordinates $\partial/\partial k$ is replaced by 1197 $\partial/\partial s$. 1198 1199 \subsubsection{Eddy induced velocity} 1200 When the \textit{eddy induced velocity} parametrisation (eiv) \citep{Gent1990} is used, 1197 1201 an additional tracer advection is introduced in combination with the isoneutral diffusion of tracers: 1198 1202 \begin{equation} \label{Eq_PE_iso+eiv} … … 1213 1217 where $A^{eiv}$ is the eddy induced velocity coefficient (or equivalently the isoneutral 1214 1218 thickness diffusivity coefficient), and $\tilde{r}_1$ and $\tilde{r}_2$ are the slopes 1215 between isoneutral and \emph{geopotential} surfaces and thus depends on the coordinate1216 considered:1219 between isoneutral and \emph{geopotential} surfaces. Their values are 1220 thus independent of the vertical coordinate, but their expression depends on the coordinate: 1217 1221 \begin{align} \label{Eq_PE_slopes_eiv} 1218 1222 \tilde{r}_n = \begin{cases} … … 1227 1231 to zero in the vicinity of the boundaries. The latter strategy is used in \NEMO (cf. Chap.~\ref{LDF}). 1228 1232 1229 \subsubsection{ lateral fourth order tracer diffusive operator}1233 \subsubsection{Lateral fourth order tracer diffusive operator} 1230 1234 1231 1235 The lateral fourth order tracer diffusive operator is defined by: … … 1239 1243 1240 1244 1241 \subsubsection{ lateral second order momentum diffusive operator}1245 \subsubsection{Lateral second order momentum diffusive operator} 1242 1246 1243 1247 The second order momentum diffusive operator along $z$- or $s$-surfaces is found by -
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trunk/DOC/TexFiles/Chapters/Chap_OBS.tex
r2483 r3294 13 13 $\ $\newline % force a new line 14 14 15 The observation and model comparison code (OBS) reads in observation files 16 (profile temperature and salinity, sea surface temperature, sea level anomaly,17 sea ice concentration, and velocity) and calculates an interpolated model equivalent 18 value at the observation location and nearest model timestep. The OBS code is 19 called from \np{opa.F90} in order to initialise the model and to calculate the 20 model equivalent values for observations on the 0th timestep. The code is then 21 called again after each timestep from \np{step.F90}. The code was originally 22 developed for use with NEMOVAR. 23 24 For all data types a 2D horizontal interpolator is needed 25 to interpolate the model fields to the observation location.26 For {\em in situ} profiles, a 1D vertical interpolator is needed in addition to 27 provide model fields at the observation depths. Currently this only works in 28 z-level model configurations, but is being developed to work with a 29 generalised vertical coordinate system. 30 Temperature data from moored buoys (TAO, TRITON, PIRATA) in the 31 ENACT/ENSEMBLES data-base are available as daily averaged quantities. For this 32 type of observation the 33 observation operator will compare such observations to the model temperature15 The observation and model comparison code (OBS) reads in observation files (profile 16 temperature and salinity, sea surface temperature, sea level anomaly, sea ice concentration, 17 and velocity) and calculates an interpolated model equivalent value at the observation 18 location and nearest model timestep. The resulting data are saved in a ``feedback'' file (or 19 files). The code was originally developed for use with the NEMOVAR data assimilation code, but 20 can be used for validation or verification of model or any other data assimilation system. 21 22 The OBS code is called from \np{opa.F90} for model initialisation and to calculate the model 23 equivalent values for observations on the 0th timestep. The code is then called again after 24 each timestep from \np{step.F90}. To build with the OBS code active \key{diaobs} must be 25 set. 26 27 For all data types a 2D horizontal interpolator is needed to interpolate the model fields to 28 the observation location. For {\em in situ} profiles, a 1D vertical interpolator is needed in 29 addition to provide model fields at the observation depths. Currently this only works in 30 z-level model configurations, but is being developed to work with a generalised vertical 31 coordinate system. Temperature data from moored buoys (TAO, TRITON, PIRATA) in the 32 ENACT/ENSEMBLES data-base are available as daily averaged quantities. For this type of 33 observation the observation operator will compare such observations to the model temperature 34 34 fields averaged over one day. The relevant observation type may be specified in the namelist 35 using \np{endailyavtypes}. Otherwise the model value from the nearest 36 timestep to the observation time is used. 37 38 The resulting data are saved in a ``feedback'' file (or files) which can be used 39 for model validation and verification and also to provide information for data 40 assimilation. This code is controlled by the namelist \textit{nam\_obs}. To 41 build with the OBS code active \key{diaobs} must be set. 42 43 Section~\ref{OBS_example} introduces a test example of the observation operator 44 code including where to obtain data and how to setup the namelist. 45 Section~\ref{OBS_details} introduces some more technical details of the 46 different observation types used and also shows a more complete namelist. 47 Finally section~\ref{OBS_theory} introduces some of the theoretical aspects of 48 the observation operator including interpolation methods and running on multiple 49 processors. 35 using \np{endailyavtypes}. Otherwise the model value from the nearest timestep to the 36 observation time is used. 37 38 The code is controlled by the namelist \textit{nam\_obs}. See the following sections for more 39 details on setting up the namelist. 40 41 Section~\ref{OBS_example} introduces a test example of the observation operator code including 42 where to obtain data and how to setup the namelist. Section~\ref{OBS_details} introduces some 43 more technical details of the different observation types used and also shows a more complete 44 namelist. Section~\ref{OBS_theory} introduces some of the theoretical aspects of the 45 observation operator including interpolation methods and running on multiple processors. 46 Section~\ref{OBS_obsutils} introduces some utilities to help working with the files produced 47 by the OBS code. 50 48 51 49 % ================================================================ … … 69 67 \item Add the following to the NEMO namelist to run the observation 70 68 operator on this data. Set the \np{enactfiles} namelist parameter to the 71 observation file name (or link in to \np{profiles\_01\.nc}):69 observation file name: 72 70 \end{enumerate} 73 71 … … 76 74 %------------------------------------------------------------------------------------------------------------- 77 75 78 The option \np{ln\_t3d} and \np{ln\_s3d} switch on the temperature and salinity76 The options \np{ln\_t3d} and \np{ln\_s3d} switch on the temperature and salinity 79 77 profile observation operator code. The \np{ln\_ena} switch turns on the reading 80 78 of ENACT/ENSEMBLES type profile data. The filename or array of filenames are … … 88 86 Setting \np{ln\_grid\_global} means that the code distributes the observations 89 87 evenly between processors. Alternatively each processor will work with 90 observations located within the model subdomain .91 92 The NEMOVAR system contains utilitiesto plot the feedback files, convert and93 recombine the files. These are available on request from the NEMOVAR team.88 observations located within the model subdomain (see section~\ref{OBS_parallel}). 89 90 A number of utilities are now provided to plot the feedback files, convert and 91 recombine the files. These are explained in more detail in section~\ref{OBS_obsutils}. 94 92 95 93 \section{Technical details} … … 713 711 714 712 \subsection{Parallel aspects of horizontal interpolation} 713 \label{OBS_parallel} 715 714 716 715 For horizontal interpolation, there is the basic problem that the … … 779 778 \subsection{Vertical interpolation operator} 780 779 781 The vertical interpolation is achieved using either a cubic spline or780 Vertical interpolation is achieved using either a cubic spline or 782 781 linear interpolation. For the cubic spline, the top and 783 782 bottom boundary conditions for the second derivative of the 784 783 interpolating polynomial in the spline are set to zero. 785 784 At the bottom boundary, this is done using the land-ocean mask. 785 786 \newpage 787 788 \section{Observation Utilities} 789 \label{OBS_obsutils} 790 791 Some tools for viewing and processing of observation and feedback files are provided in the 792 NEMO repository for convenience. These include OBSTOOLS which are a collection of Fortran 793 programs which are helpful to deal with feedback files. They do such tasks as observation file 794 conversion, printing of file contents, some basic statistical analysis of feedback files. The 795 other tool is an IDL program called dataplot which uses a graphical interface to visualise 796 observations and feedback files. OBSTOOLS and dataplot are described in more detail below. 797 798 \subsection{Obstools} 799 800 A series of Fortran utilities is provided with NEMO called OBSTOOLS. This are helpful in 801 handling observation files and the feedback file output from the NEMO observation operator. 802 The utilities are as follows 803 804 \subsubsection{corio2fb} 805 806 The program corio2fb converts profile observation files from the Coriolis format to the 807 standard feedback format. The program is called in the following way: 808 809 \begin{alltt} 810 \footnotesize 811 \begin{verbatim} 812 corio2fb.exe outputfile inputfile1 inputfile2 ... 813 \end{verbatim} 814 \end{alltt} 815 816 \subsubsection{enact2fb} 817 818 The program enact2fb converts profile observation files from the ENACT format to the standard 819 feedback format. The program is called in the following way: 820 821 \begin{alltt} 822 \footnotesize 823 \begin{verbatim} 824 enact2fb.exe outputfile inputfile1 inputfile2 ... 825 \end{verbatim} 826 \end{alltt} 827 828 \subsubsection{fbcomb} 829 830 The program fbcomb combines multiple feedback files produced by individual processors in an 831 MPI run of NEMO into a single feedback file. The program is called in the following way: 832 833 \begin{alltt} 834 \footnotesize 835 \begin{verbatim} 836 fbcomb.exe outputfile inputfile1 inputfile2 ... 837 \end{verbatim} 838 \end{alltt} 839 840 \subsubsection{fbmatchup} 841 842 The program fbmatchup will match observations from two feedback files. The program is called 843 in the following way: 844 845 \begin{alltt} 846 \footnotesize 847 \begin{verbatim} 848 fbmatchup.exe outputfile inputfile1 varname1 inputfile2 varname2 ... 849 \end{verbatim} 850 \end{alltt} 851 852 853 \subsubsection{fbprint} 854 855 The program fbprint will print the contents of a feedback file or files to standard output. 856 Selected information can be output using optional arguments. The program is called in the 857 following way: 858 859 \begin{alltt} 860 \footnotesize 861 \begin{verbatim} 862 fbprint.exe [options] inputfile 863 864 options: 865 -b shorter output 866 -q Select observations based on QC flags 867 -Q Select observations based on QC flags 868 -B Select observations based on QC flags 869 -u unsorted 870 -s ID select station ID 871 -t TYPE select observation type 872 -v NUM1-NUM2 select variable range to print by number 873 (default all) 874 -a NUM1-NUM2 select additional variable range to print by number 875 (default all) 876 -e NUM1-NUM2 select extra variable range to print by number 877 (default all) 878 -d output date range 879 -D print depths 880 -z use zipped files 881 \end{verbatim} 882 \end{alltt} 883 884 \subsubsection{fbsel} 885 886 The program fbsel will select or subsample observations. The program is called in the 887 following way: 888 889 \begin{alltt} 890 \footnotesize 891 \begin{verbatim} 892 fbsel.exe <input filename> <output filename> 893 \end{verbatim} 894 \end{alltt} 895 896 \subsubsection{fbstat} 897 898 The program fbstat will output summary statistics in different global areas into a number of 899 files. The program is called in the following way: 900 901 \begin{alltt} 902 \footnotesize 903 \begin{verbatim} 904 fbstat.exe [-nmlev] <filenames> 905 \end{verbatim} 906 \end{alltt} 907 908 \subsubsection{fbthin} 909 910 The program fbthin will thin the data to 1 degree resolution. The code could easily be 911 modified to thin to a different resolution. The program is called in the following way: 912 913 \begin{alltt} 914 \footnotesize 915 \begin{verbatim} 916 fbthin.exe inputfile outputfile 917 \end{verbatim} 918 \end{alltt} 919 920 \subsubsection{sla2fb} 921 922 The program sla2fb will convert an AVISO SLA format file to feedback format. The program is 923 called in the following way: 924 925 \begin{alltt} 926 \footnotesize 927 \begin{verbatim} 928 sla2fb.exe [-s type] outputfile inputfile1 inputfile2 ... 929 930 Option: 931 -s Select altimeter data_source 932 \end{verbatim} 933 \end{alltt} 934 935 \subsubsection{vel2fb} 936 937 The program vel2fb will convert TAO/PIRATA/RAMA currents files to feedback format. The program 938 is called in the following way: 939 940 \begin{alltt} 941 \footnotesize 942 \begin{verbatim} 943 vel2fb.exe outputfile inputfile1 inputfile2 ... 944 \end{verbatim} 945 \end{alltt} 946 947 \subsection{building the obstools} 948 949 To build the obstools use in the tools directory use ./maketools -n OBSTOOLS -m [ARCH]. 950 951 \subsection{Dataplot} 952 953 An IDL program called dataplot is included which uses a graphical interface to visualise 954 observations and feedback files. It is possible to zoom in, plot individual profiles and 955 calculate some basic statistics. To plot some data run IDL and then: 956 \begin{alltt} 957 \footnotesize 958 \begin{verbatim} 959 IDL> dataplot, "filename" 960 \end{verbatim} 961 \end{alltt} 962 963 To read multiple files into dataplot, for example multiple feedback files from different 964 processors or from different days, the easiest method is to use the spawn command to generate 965 a list of files which can then be passed to dataplot. 966 \begin{alltt} 967 \footnotesize 968 \begin{verbatim} 969 IDL> spawn, 'ls profb*.nc', files 970 IDL> dataplot, files 971 \end{verbatim} 972 \end{alltt} 973 974 Fig~\ref{fig:obsdataplotmain} shows the main window which is launched when dataplot starts. 975 This is split into three parts. At the top there is a menu bar which contains a variety of 976 drop down menus. Areas - zooms into prespecified regions; plot - plots the data as a 977 timeseries or a T-S diagram if appropriate; Find - allows data to be searched; Config - sets 978 various configuration options. 979 980 The middle part is a plot of the geographical location of the observations. This will plot the 981 observation value, the model background value or observation minus background value depending 982 on the option selected in the radio button at the bottom of the window. The plotting colour 983 range can be changed by clicking on the colour bar. The title of the plot gives some basic 984 information about the date range and depth range shown, the extreme values, and the mean and 985 rms values. It is possible to zoom in using a drag-box. You may also zoom in or out using the 986 mouse wheel. 987 988 The bottom part of the window controls what is visible in the plot above. There are two bars 989 which select the level range plotted (for profile data). The other bars below select the date 990 range shown. The bottom of the figure allows the option to plot the mean, root mean square, 991 standard deviation or mean square values. As mentioned above you can choose to plot the 992 observation value, the model background value or observation minus background value. The next 993 group of radio buttons selects the map projection. This can either be regular latitude 994 longitude grid, or north or south polar stereographic. The next group of radio buttons will 995 plot bad observations, switch to salinity and plot density for profile observations. The 996 rightmost group of buttons will print the plot window as a postscript, save it as png, or exit 997 from dataplot. 998 999 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> 1000 \begin{figure} \begin{center} 1001 %\includegraphics[width=10cm,height=12cm,angle=-90.]{./TexFiles/Figures/Fig_OBS_dataplot_main} 1002 \includegraphics[width=9cm,angle=-90.]{./TexFiles/Figures/Fig_OBS_dataplot_main} 1003 \caption{ \label{fig:obsdataplotmain} 1004 Main window of dataplot.} 1005 \end{center} \end{figure} 1006 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> 1007 1008 If a profile point is clicked with the mouse button a plot of the observation and background 1009 values as a function of depth (Fig~\ref{fig:obsdataplotprofile}). 1010 1011 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> 1012 \begin{figure} \begin{center} 1013 %\includegraphics[width=10cm,height=12cm,angle=-90.]{./TexFiles/Figures/Fig_OBS_dataplot_prof} 1014 \includegraphics[width=7cm,angle=-90.]{./TexFiles/Figures/Fig_OBS_dataplot_prof} 1015 \caption{ \label{fig:obsdataplotprofile} 1016 Profile plot from dataplot produced by right clicking on a point in the main window.} 1017 \end{center} \end{figure} 1018 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> 1019 1020 1021 1022 -
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r2541 r3294 24 24 \end{itemize} 25 25 26 F ourdifferent ways to provide the first six fields to the ocean are available which26 Five different ways to provide the first six fields to the ocean are available which 27 27 are controlled by namelist variables: an analytical formulation (\np{ln\_ana}~=~true), 28 28 a flux formulation (\np{ln\_flx}~=~true), a bulk formulae formulation (CORE 29 (\np{ln\_core}~=~true) or CLIO (\np{ln\_clio}~=~true) bulk formulae) and a coupled 29 (\np{ln\_core}~=~true), CLIO (\np{ln\_clio}~=~true) or MFS 30 \footnote { Note that MFS bulk formulae compute fluxes only for the ocean component} 31 (\np{ln\_mfs}~=~true) bulk formulae) and a coupled 30 32 formulation (exchanges with a atmospheric model via the OASIS coupler) 31 33 (\np{ln\_cpl}~=~true). When used, the atmospheric pressure forces both 32 ocean and ice dynamics (\np{ln\_apr\_dyn}~=~true) 33 \footnote{The surface pressure field could be use in bulk formulae, nevertheless 34 none of the current bulk formulea (CLIO and CORE) uses the it.}. 34 ocean and ice dynamics (\np{ln\_apr\_dyn}~=~true). 35 35 The frequency at which the six or seven fields have to be updated is the \np{nn\_fsbc} 36 36 namelist parameter. … … 46 46 (\np{nn\_ice}~=~0,1, 2 or 3); the addition of river runoffs as surface freshwater 47 47 fluxes or lateral inflow (\np{ln\_rnf}~=~true); the addition of a freshwater flux adjustment 48 in order to avoid a mean sea-level drift (\np{nn\_fwb}~=~0,~1~or~2); andthe48 in order to avoid a mean sea-level drift (\np{nn\_fwb}~=~0,~1~or~2); the 49 49 transformation of the solar radiation (if provided as daily mean) into a diurnal 50 cycle (\np{ln\_dm2dc}~=~true). 50 cycle (\np{ln\_dm2dc}~=~true); and a neutral drag coefficient can be read from an external wave 51 model (\np{ln\_cdgw}~=~true). The latter option is possible only in case core or mfs bulk formulas are selected. 51 52 52 53 In this chapter, we first discuss where the surface boundary condition appears in the 53 model equations. Then we present the f ourways of providing the surface boundary condition,54 model equations. Then we present the five ways of providing the surface boundary condition, 54 55 followed by the description of the atmospheric pressure and the river runoff. 55 56 Next the scheme for interpolation on the fly is described. … … 245 246 actual year/month/day, always coded with 4 or 2 digits. Note that (1) in mpp, if the file is split 246 247 over each subdomain, the suffix '.nc' is replaced by '\_PPPP.nc', where 'PPPP' is the 247 process number coded with 4 digits; (2) when using AGRIF, the prefix ÔN\_Õ is added to files, 248 process number coded with 4 digits; (2) when using AGRIF, the prefix 249 '\_N' is added to files, 248 250 where 'N' is the child grid number.} 249 251 \end{table} … … 480 482 % Bulk formulation 481 483 % ================================================================ 482 \section [Bulk formulation (\textit{sbcblk\_core} or \textit{sbcblk\_clio}) ]483 {Bulk formulation \small{(\mdl{sbcblk\_core} or \mdl{sbcblk\_clio} module)} }484 \section [Bulk formulation (\textit{sbcblk\_core}, \textit{sbcblk\_clio} or \textit{sbcblk\_mfs}) ] 485 {Bulk formulation \small{(\mdl{sbcblk\_core} \mdl{sbcblk\_clio} \mdl{sbcblk\_mfs} modules)} } 484 486 \label{SBC_blk} 485 487 … … 487 489 using bulk formulae and atmospheric fields and ocean (and ice) variables. 488 490 489 The atmospheric fields used depend on the bulk formulae used. T wobulk formulations490 are available : the CORE and CLIObulk formulea. The choice is made by setting to true491 one of the following namelist variable : \np{ln\_core} and \np{ln\_clio}.492 493 Note : in forced mode, when a sea-ice model is used, a bulk formulation have to be used.494 Therefore the two bulk formulea providedinclude the computation of the fluxes over both491 The atmospheric fields used depend on the bulk formulae used. Three bulk formulations 492 are available : the CORE, the CLIO and the MFS bulk formulea. The choice is made by setting to true 493 one of the following namelist variable : \np{ln\_core} ; \np{ln\_clio} or \np{ln\_mfs}. 494 495 Note : in forced mode, when a sea-ice model is used, a bulk formulation (CLIO or CORE) have to be used. 496 Therefore the two bulk (CLIO and CORE) formulea include the computation of the fluxes over both 495 497 an ocean and an ice surface. 496 498 … … 583 585 namelist (see \S\ref{SBC_fldread}). 584 586 587 % ------------------------------------------------------------------------------------------------------------- 588 % MFS Bulk formulae 589 % ------------------------------------------------------------------------------------------------------------- 590 \subsection [MFS Bulk formulea (\np{ln\_mfs}=true)] 591 {MFS Bulk formulea (\np{ln\_mfs}=true, \mdl{sbcblk\_mfs})} 592 \label{SBC_blk_mfs} 593 %------------------------------------------namsbc_mfs---------------------------------------------------- 594 \namdisplay{namsbc_mfs} 595 %---------------------------------------------------------------------------------------------------------- 596 597 The MFS (Mediterranean Forecasting System) bulk formulae have been developed by 598 \citet{Castellari_al_JMS1998}. 599 They have been designed to handle the ECMWF operational data and are currently 600 in use in the MFS operational system \citep{Tonani_al_OS08}, \citep{Oddo_al_OS09}. 601 The wind stress computation uses a drag coefficient computed according to \citet{Hellerman_Rosenstein_JPO83}. 602 The surface boundary condition for temperature involves the balance between surface solar radiation, 603 net long-wave radiation, the latent and sensible heat fluxes. 604 Solar radiation is dependent on cloud cover and is computed by means of 605 an astronomical formula \citep{Reed_JPO77}. Albedo monthly values are from \citet{Payne_JAS72} 606 as means of the values at $40^{o}N$ and $30^{o}N$ for the Atlantic Ocean (hence the same latitudinal 607 band of the Mediterranean Sea). The net long-wave radiation flux 608 \citep{Bignami_al_JGR95} is a function of 609 air temperature, sea-surface temperature, cloud cover and relative humidity. 610 Sensible heat and latent heat fluxes are computed by classical 611 bulk formulae parameterized according to \citet{Kondo1975}. 612 Details on the bulk formulae used can be found in \citet{Maggiore_al_PCE98} and \citet{Castellari_al_JMS1998}. 613 614 The required 7 input fields must be provided on the model Grid-T and are: 615 \begin{itemize} 616 \item Zonal Component of the 10m wind ($ms^{-1}$) (\np{sn\_windi}) 617 \item Meridional Component of the 10m wind ($ms^{-1}$) (\np{sn\_windj}) 618 \item Total Claud Cover (\%) (\np{sn\_clc}) 619 \item 2m Air Temperature ($K$) (\np{sn\_tair}) 620 \item 2m Dew Point Temperature ($K$) (\np{sn\_rhm}) 621 \item Total Precipitation ${Kg} m^{-2} s^{-1}$ (\np{sn\_prec}) 622 \item Mean Sea Level Pressure (${Pa}$) (\np{sn\_msl}) 623 \end{itemize} 624 % ------------------------------------------------------------------------------------------------------------- 585 625 % ================================================================ 586 626 % Coupled formulation … … 602 642 \footnote{The \key{oasis4} exist. It activates portion of the code that are still under development.}. 603 643 It has been successfully used to interface \NEMO to most of the European atmospheric 604 GCM (ARPEGE, ECHAM, ECMWF, HadAM, LMDz),644 GCM (ARPEGE, ECHAM, ECMWF, HadAM, HadGAM, LMDz), 605 645 as well as to \href{http://wrf-model.org/}{WRF} (Weather Research and Forecasting Model). 606 646 … … 610 650 When PISCES biogeochemical model (\key{top} and \key{pisces}) is also used in the coupled system, 611 651 the whole carbon cycle is computed by defining \key{cpl\_carbon\_cycle}. In this case, 612 CO$_2$ fluxes are exchanged between the atmosphere and the ice-ocean system. 652 CO$_2$ fluxes will be exchanged between the atmosphere and the ice-ocean system (and need to be activated 653 in namsbc{\_}cpl). 654 655 The new namelist above allows control of various aspects of the coupling fields (particularly for 656 vectors) and now allows for any coupling fields to have multiple sea ice categories (as required by LIM3 657 and CICE). When indicating a multi-category coupling field in namsbc{\_}cpl the number of categories will be 658 determined by the number used in the sea ice model. In some limited cases it may be possible to specify 659 single category coupling fields even when the sea ice model is running with multiple categories - in this 660 case the user should examine the code to be sure the assumptions made are satisfactory. In cases where 661 this is definitely not possible the model should abort with an error message. The new code has been tested using 662 ECHAM with LIM2, and HadGAM3 with CICE but although it will compile with \key{lim3} additional minor code changes 663 may be required to run using LIM3. 613 664 614 665 … … 645 696 646 697 % ================================================================ 698 % Tidal Potential 699 % ================================================================ 700 \section [Tidal Potential (\textit{sbctide})] 701 {Tidal Potential (\mdl{sbctide})} 702 \label{SBC_tide} 703 704 A module is available to use the tidal potential forcing and is activated with with \key{tide}. 705 706 707 %------------------------------------------nam_tide---------------------------------------------------- 708 \namdisplay{nam_tide} 709 %------------------------------------------------------------------------------------------------------------- 710 711 Concerning the tidal potential, some parameters are available in namelist: 712 713 - \texttt{ln\_tide\_pot} activate the tidal potential forcing 714 715 - \texttt{nb\_harmo} is the number of constituent used 716 717 - \texttt{clname} is the name of constituent 718 719 720 The tide is generated by the forces of gravity ot the Earth-Moon and Earth-Sun sytem; 721 they are expressed as the gradient of the astronomical potential ($\vec{\nabla}\Pi_{a}$). \\ 722 723 The potential astronomical expressed, for the three types of tidal frequencies 724 following, by : \\ 725 Tide long period : 726 \begin{equation} 727 \Pi_{a}=gA_{k}(\frac{1}{2}-\frac{3}{2}sin^{2}\phi)cos(\omega_{k}t+V_{0k}) 728 \end{equation} 729 diurnal Tide : 730 \begin{equation} 731 \Pi_{a}=gA_{k}(sin 2\phi)cos(\omega_{k}t+\lambda+V_{0k}) 732 \end{equation} 733 Semi-diurnal tide: 734 \begin{equation} 735 \Pi_{a}=gA_{k}(cos^{2}\phi)cos(\omega_{k}t+2\lambda+V_{0k}) 736 \end{equation} 737 738 739 $A_{k}$ is the amplitude of the wave k, $\omega_{k}$ the pulsation of the wave k, $V_{0k}$ the astronomical phase of the wave 740 $k$ to Greenwich. 741 742 We make corrections to the astronomical potential. 743 We obtain : 744 \begin{equation} 745 \Pi-g\delta = (1+k-h) \Pi_{A}(\lambda,\phi) 746 \end{equation} 747 with $k$ a number of Love estimated to 0.6 which parametrized the astronomical tidal land, 748 and $h$ a number of Love to 0.3 which parametrized the parametrization due to the astronomical tidal land. 749 750 % ================================================================ 647 751 % River runoffs 648 752 % ================================================================ … … 759 863 %To do this we need to treat evaporation/precipitation fluxes and river runoff differently in the tra_sbc module. We decided to separate them throughout the code, so that the variable emp represented solely evaporation minus precipitation fluxes, and a new 2d variable rnf was added which represents the volume flux of river runoff (in kg/m2s to remain consistent with emp). This meant many uses of emp and emps needed to be changed, a list of all modules which use emp or emps and the changes made are below: 760 864 761 }865 %} 762 866 763 867 % ================================================================ … … 909 1013 ice-ocean fluxes, that are combined with the air-sea fluxes using the ice fraction of 910 1014 each model cell to provide the surface ocean fluxes. Note that the activation of a 911 sea-ice model is is done by defining a CPP key (\key{lim2} or \key{lim3}).912 The activation automatically ove writethe read value of nn{\_}ice to its appropriate913 value ($i.e.$ $2$ for LIM-2 and $3$ for LIM-3).1015 sea-ice model is is done by defining a CPP key (\key{lim2}, \key{lim3} or \key{cice}). 1016 The activation automatically overwrites the read value of nn{\_}ice to its appropriate 1017 value ($i.e.$ $2$ for LIM-2, $3$ for LIM-3 or $4$ for CICE). 914 1018 \end{description} 915 1019 916 1020 % {Description of Ice-ocean interface to be added here or in LIM 2 and 3 doc ?} 1021 1022 \subsection [Interface to CICE (\textit{sbcice\_cice})] 1023 {Interface to CICE (\mdl{sbcice\_cice})} 1024 \label{SBC_cice} 1025 1026 It is now possible to couple a global NEMO configuration (without AGRIF) to the CICE sea-ice 1027 model by using \key{cice}. The CICE code can be obtained from 1028 \href{http://oceans11.lanl.gov/trac/CICE/}{LANL} and the additional 'hadgem3' drivers will be required, 1029 even with the latest code release. Input grid files consistent with those used in NEMO will also be needed, 1030 and CICE CPP keys \textbf{ORCA\_GRID}, \textbf{CICE\_IN\_NEMO} and \textbf{coupled} should be used (seek advice from UKMO 1031 if necessary). Currently the code is only designed to work when using the CORE forcing option for NEMO (with 1032 \textit{calc\_strair~=~true} and \textit{calc\_Tsfc~=~true} in the CICE name-list), or alternatively when NEMO 1033 is coupled to the HadGAM3 atmosphere model (with \textit{calc\_strair~=~false} and \textit{calc\_Tsfc~=~false}). 1034 The code is intended to be used with \np{nn\_fsbc} set to 1 (although coupling ocean and ice less frequently 1035 should work, it is possible the calculation of some of the ocean-ice fluxes needs to be modified slightly - the 1036 user should check that results are not significantly different to the standard case). 1037 1038 There are two options for the technical coupling between NEMO and CICE. The standard version allows 1039 complete flexibility for the domain decompositions in the individual models, but this is at the expense of global 1040 gather and scatter operations in the coupling which become very expensive on larger numbers of processors. The 1041 alternative option (using \key{nemocice\_decomp} for both NEMO and CICE) ensures that the domain decomposition is 1042 identical in both models (provided domain parameters are set appropriately, and 1043 \textit{processor\_shape~=~square-ice} and \textit{distribution\_wght~=~block} in the CICE name-list) and allows 1044 much more efficient direct coupling on individual processors. This solution scales much better although it is at 1045 the expense of having more idle CICE processors in areas where there is no sea ice. 1046 917 1047 918 1048 % ------------------------------------------------------------------------------------------------------------- … … 938 1068 \end{description} 939 1069 1070 % ------------------------------------------------------------------------------------------------------------- 1071 % Neutral Drag Coefficient from external wave model 1072 % ------------------------------------------------------------------------------------------------------------- 1073 \subsection [Neutral drag coefficient from external wave model (\textit{sbcwave})] 1074 {Neutral drag coefficient from external wave model (\mdl{sbcwave})} 1075 \label{SBC_wave} 1076 %------------------------------------------namwave---------------------------------------------------- 1077 \namdisplay{namsbc_wave} 1078 %------------------------------------------------------------------------------------------------------------- 1079 \begin{description} 1080 1081 \item [??] In order to read a neutral drag coeff, from an external data source (i.e. a wave model), the 1082 logical variable \np{ln\_cdgw} 1083 in $namsbc$ namelist must be defined ${.true.}$. 1084 The \mdl{sbcwave} module containing the routine \np{sbc\_wave} reads the 1085 namelist ${namsbc\_wave}$ (for external data names, locations, frequency, interpolation and all 1086 the miscellanous options allowed by Input Data generic Interface see \S\ref{SBC_input}) 1087 and a 2D field of neutral drag coefficient. Then using the routine 1088 TURB\_CORE\_1Z or TURB\_CORE\_2Z, and starting from the neutral drag coefficent provided, the drag coefficient is computed according 1089 to stable/unstable conditions of the air-sea interface following \citet{Large_Yeager_Rep04}. 1090 1091 \end{description} 1092 940 1093 % Griffies doc: 941 1094 % When running ocean-ice simulations, we are not explicitly representing land processes, such as rivers, catchment areas, snow accumulation, etc. However, to reduce model drift, it is important to balance the hydrological cycle in ocean-ice models. We thus need to prescribe some form of global normalization to the precipitation minus evaporation plus river runoff. The result of the normalization should be a global integrated zero net water input to the ocean-ice system over a chosen time scale. … … 944 1097 945 1098 946 -
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trunk/DOC/TexFiles/Chapters/Chap_TRA.tex
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r2541 r3294 491 491 \label{TRA_ldf_iso} 492 492 493 The general form of the second order lateral tracer subgrid scale physics 493 If the Griffies trad scheme is not employed 494 (\np{ln\_traldf\_grif}=true; see App.\ref{sec:triad}) the general form of the second order lateral tracer subgrid scale physics 494 495 (\ref{Eq_PE_zdf}) takes the following semi-discrete space form in $z$- and 495 496 $s$-coordinates: … … 536 537 (see \S\ref{LDF}) allows the model to run safely without any additional 537 538 background horizontal diffusion \citep{Guilyardi_al_CD01}. An alternative scheme 538 developed by \cite{Griffies_al_JPO98} which preserves both tracer and its variance539 developed by \cite{Griffies_al_JPO98} which ensures tracer variance decreases 539 540 is also available in \NEMO (\np{ln\_traldf\_grif}=true). A complete description of 540 the algorithm is given in App.\ref{ Apdx_Griffies}.541 the algorithm is given in App.\ref{sec:triad}. 541 542 542 543 Note that in the partial step $z$-coordinate (\np{ln\_zps}=true), the horizontal … … 1053 1054 %--------------------------------------------namtra_dmp------------------------------------------------- 1054 1055 \namdisplay{namtra_dmp} 1055 \namdisplay{namdta_tem}1056 \namdisplay{namdta_sal}1057 1056 %-------------------------------------------------------------------------------------------------------------- 1058 1057 … … 1067 1066 where $\gamma$ is the inverse of a time scale, and $T_o$ and $S_o$ 1068 1067 are given temperature and salinity fields (usually a climatology). 1069 The restoring term is added when \key{tradmp} is defined.1070 It also requires that both \ key{dtatem} and \key{dtasal} are defined1071 and fill in \textit{namdta\_tem} and \textit{namdta\_sal namelists}1072 ($i.e.$ that $T_o$ and $S_o$ are read using \mdl{fldread},1073 see \S\ref{SBC_fldread}). The restoring coefficient $\gamma$ is1074 a three-dimensional array initialized by the user in routine \rou{dtacof}1075 also located in module \mdl{tradmp}.1068 The restoring term is added when the namelist parameter \np{ln\_tradmp} is set to true. 1069 It also requires that both \np{ln\_tsd\_init} and \np{ln\_tsd\_tradmp} are set to true 1070 in \textit{namtsd} namelist as well as \np{sn\_tem} and \np{sn\_sal} structures are 1071 correctly set ($i.e.$ that $T_o$ and $S_o$ are provided in input files and read 1072 using \mdl{fldread}, see \S\ref{SBC_fldread}). 1073 The restoring coefficient $\gamma$ is a three-dimensional array initialized by the 1074 user in routine \rou{dtacof} also located in module \mdl{tradmp}. 1076 1075 1077 1076 The two main cases in which \eqref{Eq_tra_dmp} is used are \textit{(a)} -
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r2541 r3294 1 1 % ================================================================ 2 % Chapter ÑVertical Ocean Physics (ZDF)2 % Chapter Vertical Ocean Physics (ZDF) 3 3 % ================================================================ 4 4 \chapter{Vertical Ocean Physics (ZDF)} … … 100 100 $a=5$ and $n=2$. The last three values can be modified by setting the 101 101 \np{rn\_avmri}, \np{rn\_alp} and \np{nn\_ric} namelist parameters, respectively. 102 103 A simple mixing-layer model to transfer and dissipate the atmospheric 104 forcings (wind-stress and buoyancy fluxes) can be activated setting 105 the \np{ln\_mldw} =.true. in the namelist. 106 107 In this case, the local depth of turbulent wind-mixing or "Ekman depth" 108 $h_{e}(x,y,t)$ is evaluated and the vertical eddy coefficients prescribed within this layer. 109 110 This depth is assumed proportional to the "depth of frictional influence" that is limited by rotation: 111 \begin{equation} 112 h_{e} = Ek \frac {u^{*}} {f_{0}} \\ 113 \end{equation} 114 where, $Ek$ is an empirical parameter, $u^{*}$ is the friction velocity and $f_{0}$ is the Coriolis 115 parameter. 116 117 In this similarity height relationship, the turbulent friction velocity: 118 \begin{equation} 119 u^{*} = \sqrt \frac {|\tau|} {\rho_o} \\ 120 \end{equation} 121 122 is computed from the wind stress vector $|\tau|$ and the reference dendity $ \rho_o$. 123 The final $h_{e}$ is further constrained by the adjustable bounds \np{rn\_mldmin} and \np{rn\_mldmax}. 124 Once $h_{e}$ is computed, the vertical eddy coefficients within $h_{e}$ are set to 125 the empirical values \np{rn\_wtmix} and \np{rn\_wvmix} \citep{Lermusiaux2001}. 102 126 103 127 % ------------------------------------------------------------------------------------------------------------- … … 539 563 the clipping factor is of crucial importance for the entrainment depth predicted in 540 564 stably stratified situations, and that its value has to be chosen in accordance 541 with the algebraic model for the turbulent ßuxes. The clipping is only activated565 with the algebraic model for the turbulent fluxes. The clipping is only activated 542 566 if \np{ln\_length\_lim}=true, and the $c_{lim}$ is set to the \np{rn\_clim\_galp} value. 543 567 … … 981 1005 reduced as necessary to ensure stability; these changes are not reported. 982 1006 1007 Limits on the bottom friction coefficient are not imposed if the user has elected to 1008 handle the bottom friction implicitly (see \S\ref{ZDF_bfr_imp}). The number of potential 1009 breaches of the explicit stability criterion are still reported for information purposes. 1010 1011 % ------------------------------------------------------------------------------------------------------------- 1012 % Implicit Bottom Friction 1013 % ------------------------------------------------------------------------------------------------------------- 1014 \subsection{Implicit Bottom Friction (\np{ln\_bfrimp}$=$\textit{T})} 1015 \label{ZDF_bfr_imp} 1016 1017 An optional implicit form of bottom friction has been implemented to improve 1018 model stability. We recommend this option for shelf sea and coastal ocean applications, especially 1019 for split-explicit time splitting. This option can be invoked by setting \np{ln\_bfrimp} 1020 to \textit{true} in the \textit{nambfr} namelist. This option requires \np{ln\_zdfexp} to be \textit{false} 1021 in the \textit{namzdf} namelist. 1022 1023 This implementation is realised in \mdl{dynzdf\_imp} and \mdl{dynspg\_ts}. In \mdl{dynzdf\_imp}, the 1024 bottom boundary condition is implemented implicitly. 1025 1026 \begin{equation} \label{Eq_dynzdf_bfr} 1027 \left.{\left( {\frac{A^{vm} }{e_3 }\ \frac{\partial \textbf{U}_h}{\partial k}} \right)} \right|_{mbk} 1028 = \binom{c_{b}^{u}u^{n+1}_{mbk}}{c_{b}^{v}v^{n+1}_{mbk}} 1029 \end{equation} 1030 1031 where $mbk$ is the layer number of the bottom wet layer. superscript $n+1$ means the velocity used in the 1032 friction formula is to be calculated, so, it is implicit. 1033 1034 If split-explicit time splitting is used, care must be taken to avoid the double counting of 1035 the bottom friction in the 2-D barotropic momentum equations. As NEMO only updates the barotropic 1036 pressure gradient and Coriolis' forcing terms in the 2-D barotropic calculation, we need to remove 1037 the bottom friction induced by these two terms which has been included in the 3-D momentum trend 1038 and update it with the latest value. On the other hand, the bottom friction contributed by the 1039 other terms (e.g. the advection term, viscosity term) has been included in the 3-D momentum equations 1040 and should not be added in the 2-D barotropic mode. 1041 1042 The implementation of the implicit bottom friction in \mdl{dynspg\_ts} is done in two steps as the 1043 following: 1044 1045 \begin{equation} \label{Eq_dynspg_ts_bfr1} 1046 \frac{\textbf{U}_{med}-\textbf{U}^{m-1}}{2\Delta t}=-g\nabla\eta-f\textbf{k}\times\textbf{U}^{m}+c_{b} 1047 \left(\textbf{U}_{med}-\textbf{U}^{m-1}\right) 1048 \end{equation} 1049 \begin{equation} \label{Eq_dynspg_ts_bfr2} 1050 \frac{\textbf{U}^{m+1}-\textbf{U}_{med}}{2\Delta t}=\textbf{T}+ 1051 \left(g\nabla\eta^{'}+f\textbf{k}\times\textbf{U}^{'}\right)- 1052 2\Delta t_{bc}c_{b}\left(g\nabla\eta^{'}+f\textbf{k}\times\textbf{u}_{b}\right) 1053 \end{equation} 1054 1055 where $\textbf{T}$ is the vertical integrated 3-D momentum trend. We assume the leap-frog time-stepping 1056 is used here. $\Delta t$ is the barotropic mode time step and $\Delta t_{bc}$ is the baroclinic mode time step. 1057 $c_{b}$ is the friction coefficient. $\eta$ is the sea surface level calculated in the barotropic loops 1058 while $\eta^{'}$ is the sea surface level used in the 3-D baroclinic mode. $\textbf{u}_{b}$ is the bottom 1059 layer horizontal velocity. 1060 1061 1062 1063 983 1064 % ------------------------------------------------------------------------------------------------------------- 984 1065 % Bottom Friction with split-explicit time splitting 985 1066 % ------------------------------------------------------------------------------------------------------------- 986 \subsection{Bottom Friction with split-explicit time splitting }1067 \subsection{Bottom Friction with split-explicit time splitting (\np{ln\_bfrimp}$=$\textit{F})} 987 1068 \label{ZDF_bfr_ts} 988 1069 … … 993 1074 {\key{dynspg\_flt}). Extra attention is required, however, when using 994 1075 split-explicit time stepping (\key{dynspg\_ts}). In this case the free surface 995 equation is solved with a small time step \np{ nn\_baro}*\np{rn\_rdt}, while the three996 dimensional prognostic variables are solved with a longer time step that is a997 multiple of \np{rn\_rdt}. The trend in the barotropic momentum due to bottom1076 equation is solved with a small time step \np{rn\_rdt}/\np{nn\_baro}, while the three 1077 dimensional prognostic variables are solved with the longer time step 1078 of \np{rn\_rdt} seconds. The trend in the barotropic momentum due to bottom 998 1079 friction appropriate to this method is that given by the selected parameterisation 999 1080 ($i.e.$ linear or non-linear bottom friction) computed with the evolving velocities … … 1018 1099 \end{enumerate} 1019 1100 1020 Note that the use of an implicit formulation 1101 Note that the use of an implicit formulation within the barotropic loop 1021 1102 for the bottom friction trend means that any limiting of the bottom friction coefficient 1022 1103 in \mdl{dynbfr} does not adversely affect the solution when using split-explicit time 1023 1104 splitting. This is because the major contribution to bottom friction is likely to come from 1024 the barotropic component which uses the unrestricted value of the coefficient. 1025 1026 The implicit formulation takes the form: 1105 the barotropic component which uses the unrestricted value of the coefficient. However, if the 1106 limiting is thought to be having a major effect (a more likely prospect in coastal and shelf seas 1107 applications) then the fully implicit form of the bottom friction should be used (see \S\ref{ZDF_bfr_imp} ) 1108 which can be selected by setting \np{ln\_bfrimp} $=$ \textit{true}. 1109 1110 Otherwise, the implicit formulation takes the form: 1027 1111 \begin{equation} \label{Eq_zdfbfr_implicitts} 1028 1112 \bar{U}^{t+ \rdt} = \; \left [ \bar{U}^{t-\rdt}\; + 2 \rdt\;RHS \right ] / \left [ 1 - 2 \rdt \;c_b^{u} / H_e \right ] … … 1091 1175 The essential goal of the parameterization is to represent the momentum 1092 1176 exchange between the barotropic tides and the unrepresented internal waves 1093 induced by the tidal ßow over rough topography in a stratified ocean.1177 induced by the tidal flow over rough topography in a stratified ocean. 1094 1178 In the current version of \NEMO, the map is built from the output of 1095 1179 the barotropic global ocean tide model MOG2D-G \citep{Carrere_Lyard_GRL03}. -
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r2570 r3294 63 63 \citep{OASIS2006}. Two-way nesting is also available through an interface to the 64 64 AGRIF package (Adaptative Grid Refinement in \textsc{Fortran}) \citep{Debreu_al_CG2008}. 65 The interface code for coupling to an alternative sea ice model (CICE, \citet{Hunke2008}) is now 66 available although this is currently only designed for global domains, without the use of AGRIF. 65 67 66 68 Other model characteristics are the lateral boundary conditions (chapter~\ref{LBC}). … … 200 202 concern of improving the model performance. 201 203 204 \vspace{1cm} 205 $\bullet$ The main modifications from NEMO/OPA v3.3 and v3.4 are :\\ 206 \begin{enumerate} 207 \item finalisation of above iso-neutral mixing \citep{Griffies_al_JPO98}"; 208 \item "Neptune effect" parametrisation; 209 \item horizontal pressure gradient suitable for s-coordinate; 210 \item semi-implicit bottom friction; 211 \item finalisation of the merge of passive and active tracers advection-diffusion modules; 212 \item a new bulk formulae (so-called MFS); 213 \item use fldread for the off-line tracer component (OFF\_SRC) ; 214 \item use MPI point to point communications for north fold; 215 \item diagnostic of transport ; 216 \end{enumerate} 217 218
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