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branches/2017/dev_merge_2017/DOC/tex_sub/chap_model_basics.tex
r9407 r9414 648 648 649 649 In fact one is totally free to choose any space and time vertical coordinate by introducing an arbitrary vertical coordinate : 650 \begin{equation} \label{eq: s}650 \begin{equation} \label{eq:PE_s} 651 651 s=s(i,j,k,t) 652 652 \end{equation} 653 with the restriction that the above equation gives a single-valued monotonic relationship between $s$ and $k$, when $i$, $j$ and $t$ are held fixed. \autoref{eq: s} is a transformation from the $(i,j,k,t)$ coordinate system with independent variables into the $(i,j,s,t)$ generalised coordinate system with $s$ depending on the other three variables through \autoref{eq:s}.653 with the restriction that the above equation gives a single-valued monotonic relationship between $s$ and $k$, when $i$, $j$ and $t$ are held fixed. \autoref{eq:PE_s} is a transformation from the $(i,j,k,t)$ coordinate system with independent variables into the $(i,j,s,t)$ generalised coordinate system with $s$ depending on the other three variables through \autoref{eq:PE_s}. 654 654 This so-called \textit{generalised vertical coordinate} \citep{Kasahara_MWR74} is in fact an Arbitrary Lagrangian--Eulerian (ALE) coordinate. Indeed, choosing an expression for $s$ is an arbitrary choice that determines which part of the vertical velocity (defined from a fixed referential) will cross the levels (Eulerian part) and which part will be used to move them (Lagrangian part). 655 655 The coordinate is also sometime referenced as an adaptive coordinate \citep{Hofmeister_al_OM09}, since the coordinate system is adapted in the course of the simulation. Its most often used implementation is via an ALE algorithm, in which a pure lagrangian step is followed by regridding and remapping steps, the later step implicitly embedding the vertical advection \citep{Hirt_al_JCP74, Chassignet_al_JPO03, White_al_JCP09}. Here we follow the \citep{Kasahara_MWR74} strategy : a regridding step (an update of the vertical coordinate) followed by an eulerian step with an explicit computation of vertical advection relative to the moving s-surfaces. … … 715 715 \vspace{0.5cm} 716 716 $\bullet$ Vector invariant form of the momentum equation : 717 \begin{multline} \label{eq:PE_sco_u }717 \begin{multline} \label{eq:PE_sco_u_vector} 718 718 \frac{\partial u }{\partial t}= 719 719 + \left( {\zeta +f} \right)\,v … … 724 724 + D_u^{\vect{U}} + F_u^{\vect{U}} \quad 725 725 \end{multline} 726 \begin{multline} \label{eq:PE_sco_v }726 \begin{multline} \label{eq:PE_sco_v_vector} 727 727 \frac{\partial v }{\partial t}= 728 728 - \left( {\zeta +f} \right)\,u … … 735 735 736 736 \vspace{0.5cm} 737 $\bullet$ Vector invariantform of the momentum equation :738 \begin{multline} \label{eq:PE_sco_u }737 $\bullet$ Flux form of the momentum equation : 738 \begin{multline} \label{eq:PE_sco_u_flux} 739 739 \frac{1}{e_3} \frac{\partial \left( e_3\,u \right) }{\partial t}= 740 740 + \left( { f + \frac{1}{e_1 \; e_2 } … … 749 749 + D_u^{\vect{U}} + F_u^{\vect{U}} \quad 750 750 \end{multline} 751 \begin{multline} \label{eq:PE_sco_v }751 \begin{multline} \label{eq:PE_sco_v_flux} 752 752 \frac{1}{e_3} \frac{\partial \left( e_3\,v \right) }{\partial t}= 753 753 - \left( { f + \frac{1}{e_1 \; e_2} … … 1138 1138 rotation between geopotential and $s$-surfaces, while it is only an approximation 1139 1139 for the rotation between isoneutral and $z$- or $s$-surfaces. Indeed, in the latter 1140 case, two assumptions are made to simplify 1140 case, two assumptions are made to simplify \autoref{eq:PE_iso_tensor} \citep{Cox1987}. 1141 1141 First, the horizontal contribution of the dianeutral mixing is neglected since the ratio 1142 1142 between iso and dia-neutral diffusive coefficients is known to be several orders of
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