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Changeset 12143 for NEMO/branches/2019/ENHANCE-02_ISF_nemo/doc/latex/NEMO/subfiles/chap_LDF.tex – NEMO

Ignore:
Timestamp:
2019-12-10T12:57:49+01:00 (4 years ago)
Author:
mathiot
Message:

update ENHANCE-02_ISF_nemo to 12072 (sette in progress)

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NEMO/branches/2019/ENHANCE-02_ISF_nemo/doc
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  • NEMO/branches/2019/ENHANCE-02_ISF_nemo/doc/latex/NEMO/subfiles/chap_LDF.tex

    r11179 r12143  
    33\begin{document} 
    44 
    5 % ================================================================ 
    6 % Chapter Lateral Ocean Physics (LDF) 
    7 % ================================================================ 
    85\chapter{Lateral Ocean Physics (LDF)} 
    96\label{chap:LDF} 
    107 
    11 \minitoc 
    12  
    13 \newpage 
    14  
    15 The lateral physics terms in the momentum and tracer equations have been described in \autoref{eq:PE_zdf} and 
     8\thispagestyle{plain} 
     9 
     10\chaptertoc 
     11 
     12\paragraph{Changes record} ~\\ 
     13 
     14{\footnotesize 
     15  \begin{tabularx}{\textwidth}{l||X|X} 
     16    Release & Author(s) & Modifications \\ 
     17    \hline 
     18    {\em   4.0} & {\em ...} & {\em ...} \\ 
     19    {\em   3.6} & {\em ...} & {\em ...} \\ 
     20    {\em   3.4} & {\em ...} & {\em ...} \\ 
     21    {\em <=3.4} & {\em ...} & {\em ...} 
     22  \end{tabularx} 
     23} 
     24 
     25\clearpage 
     26 
     27The lateral physics terms in the momentum and tracer equations have been described in \autoref{eq:MB_zdf} and 
    1628their discrete formulation in \autoref{sec:TRA_ldf} and \autoref{sec:DYN_ldf}). 
    1729In this section we further discuss each lateral physics option. 
     
    2234(3) the space and time variations of the eddy coefficients. 
    2335These three aspects of the lateral diffusion are set through namelist parameters 
    24 (see the \ngn{nam\_traldf} and \ngn{nam\_dynldf} below). 
    25 Note that this chapter describes the standard implementation of iso-neutral tracer mixing, 
    26 and Griffies's implementation, which is used if \np{traldf\_grif}\forcode{ = .true.}, 
    27 is described in Appdx\autoref{apdx:triad} 
    28  
    29 %-----------------------------------nam_traldf - nam_dynldf-------------------------------------------- 
    30  
    31 \nlst{namtra_ldf}  
    32  
    33 \nlst{namdyn_ldf}  
    34 %-------------------------------------------------------------------------------------------------------------- 
    35  
    36  
    37 % ================================================================ 
    38 % Direction of lateral Mixing 
    39 % ================================================================ 
    40 \section[Direction of lateral mixing (\textit{ldfslp.F90})] 
    41 {Direction of lateral mixing (\protect\mdl{ldfslp})} 
     36(see the \nam{tra_ldf}{tra\_ldf} and \nam{dyn_ldf}{dyn\_ldf} below). 
     37Note that this chapter describes the standard implementation of iso-neutral tracer mixing. 
     38Griffies's implementation, which is used if \np[=.true.]{ln_traldf_triad}{ln\_traldf\_triad}, 
     39is described in \autoref{apdx:TRIADS} 
     40 
     41%% ================================================================================================= 
     42\section[Lateral mixing operators]{Lateral mixing operators} 
     43\label{sec:LDF_op} 
     44We remind here the different lateral mixing operators that can be used. Further details can be found in \autoref{subsec:TRA_ldf_op} and  \autoref{sec:DYN_ldf}. 
     45 
     46%% ================================================================================================= 
     47\subsection[No lateral mixing (\forcode{ln_traldf_OFF} \& \forcode{ln_dynldf_OFF})]{No lateral mixing (\protect\np{ln_traldf_OFF}{ln\_traldf\_OFF} \& \protect\np{ln_dynldf_OFF}{ln\_dynldf\_OFF})} 
     48 
     49It is possible to run without explicit lateral diffusion on tracers (\protect\np[=.true.]{ln_traldf_OFF}{ln\_traldf\_OFF}) and/or 
     50momentum (\protect\np[=.true.]{ln_dynldf_OFF}{ln\_dynldf\_OFF}). The latter option is even recommended if using the 
     51UBS advection scheme on momentum (\np[=.true.]{ln_dynadv_ubs}{ln\_dynadv\_ubs}, 
     52see \autoref{subsec:DYN_adv_ubs}) and can be useful for testing purposes. 
     53 
     54%% ================================================================================================= 
     55\subsection[Laplacian mixing (\forcode{ln_traldf_lap} \& \forcode{ln_dynldf_lap})]{Laplacian mixing (\protect\np{ln_traldf_lap}{ln\_traldf\_lap} \& \protect\np{ln_dynldf_lap}{ln\_dynldf\_lap})} 
     56Setting \protect\np[=.true.]{ln_traldf_lap}{ln\_traldf\_lap} and/or \protect\np[=.true.]{ln_dynldf_lap}{ln\_dynldf\_lap} enables 
     57a second order diffusion on tracers and momentum respectively. Note that in \NEMO\ 4, one can not combine 
     58Laplacian and Bilaplacian operators for the same variable. 
     59 
     60%% ================================================================================================= 
     61\subsection[Bilaplacian mixing (\forcode{ln_traldf_blp} \& \forcode{ln_dynldf_blp})]{Bilaplacian mixing (\protect\np{ln_traldf_blp}{ln\_traldf\_blp} \& \protect\np{ln_dynldf_blp}{ln\_dynldf\_blp})} 
     62Setting \protect\np[=.true.]{ln_traldf_blp}{ln\_traldf\_blp} and/or \protect\np[=.true.]{ln_dynldf_blp}{ln\_dynldf\_blp} enables 
     63a fourth order diffusion on tracers and momentum respectively. It is implemented by calling the above Laplacian operator twice. 
     64We stress again that from \NEMO\ 4, the simultaneous use Laplacian and Bilaplacian operators is not allowed. 
     65 
     66%% ================================================================================================= 
     67\section[Direction of lateral mixing (\textit{ldfslp.F90})]{Direction of lateral mixing (\protect\mdl{ldfslp})} 
    4268\label{sec:LDF_slp} 
    4369 
    44 %%% 
    45 \gmcomment{ 
     70\cmtgm{ 
    4671  we should emphasize here that the implementation is a rather old one. 
    4772  Better work can be achieved by using \citet{griffies.gnanadesikan.ea_JPO98, griffies_bk04} iso-neutral scheme. 
     
    5075A direction for lateral mixing has to be defined when the desired operator does not act along the model levels. 
    5176This occurs when $(a)$ horizontal mixing is required on tracer or momentum 
    52 (\np{ln\_traldf\_hor} or \np{ln\_dynldf\_hor}) in $s$- or mixed $s$-$z$- coordinates, 
     77(\np{ln_traldf_hor}{ln\_traldf\_hor} or \np{ln_dynldf_hor}{ln\_dynldf\_hor}) in $s$- or mixed $s$-$z$- coordinates, 
    5378and $(b)$ isoneutral mixing is required whatever the vertical coordinate is. 
    5479This direction of mixing is defined by its slopes in the \textbf{i}- and \textbf{j}-directions at the face of 
    5580the cell of the quantity to be diffused. 
    5681For a tracer, this leads to the following four slopes: 
    57 $r_{1u}$, $r_{1w}$, $r_{2v}$, $r_{2w}$ (see \autoref{eq:tra_ldf_iso}), 
     82$r_{1u}$, $r_{1w}$, $r_{2v}$, $r_{2w}$ (see \autoref{eq:TRA_ldf_iso}), 
    5883while for momentum the slopes are  $r_{1t}$, $r_{1uw}$, $r_{2f}$, $r_{2uw}$ for $u$ and 
    59 $r_{1f}$, $r_{1vw}$, $r_{2t}$, $r_{2vw}$ for $v$.  
    60  
    61 %gm% add here afigure of the slope in i-direction 
    62  
     84$r_{1f}$, $r_{1vw}$, $r_{2t}$, $r_{2vw}$ for $v$. 
     85 
     86\cmtgm{Add here afigure of the slope in i-direction} 
     87 
     88%% ================================================================================================= 
    6389\subsection{Slopes for tracer geopotential mixing in the $s$-coordinate} 
    6490 
    65 In $s$-coordinates, geopotential mixing (\ie horizontal mixing) $r_1$ and $r_2$ are the slopes between 
     91In $s$-coordinates, geopotential mixing (\ie\ horizontal mixing) $r_1$ and $r_2$ are the slopes between 
    6692the geopotential and computational surfaces. 
    67 Their discrete formulation is found by locally solving \autoref{eq:tra_ldf_iso} when 
     93Their discrete formulation is found by locally solving \autoref{eq:TRA_ldf_iso} when 
    6894the diffusive fluxes in the three directions are set to zero and $T$ is assumed to be horizontally uniform, 
    69 \ie a linear function of $z_T$, the depth of a $T$-point.  
    70 %gm { Steven : My version is obviously wrong since I'm left with an arbitrary constant which is the local vertical temperature gradient} 
    71  
    72 \begin{equation} 
    73   \label{eq:ldfslp_geo} 
     95\ie\ a linear function of $z_T$, the depth of a $T$-point. 
     96\cmtgm{Steven : My version is obviously wrong since 
     97  I'm left with an arbitrary constant which is the local vertical temperature gradient} 
     98 
     99\begin{equation} 
     100  \label{eq:LDF_slp_geo} 
    74101  \begin{aligned} 
    75102    r_{1u} &= \frac{e_{3u}}{ \left( e_{1u}\;\overline{\overline{e_{3w}}}^{\,i+1/2,\,k} \right)} 
     
    86113\end{equation} 
    87114 
    88 %gm%  caution I'm not sure the simplification was a good idea!  
    89  
    90 These slopes are computed once in \rou{ldfslp\_init} when \np{ln\_sco}\forcode{ = .true.}rue, 
    91 and either \np{ln\_traldf\_hor}\forcode{ = .true.} or \np{ln\_dynldf\_hor}\forcode{ = .true.}.  
    92  
     115\cmtgm{Caution I'm not sure the simplification was a good idea!} 
     116 
     117These slopes are computed once in \rou{ldf\_slp\_init} when \np[=.true.]{ln_sco}{ln\_sco}, 
     118and either \np[=.true.]{ln_traldf_hor}{ln\_traldf\_hor} or \np[=.true.]{ln_dynldf_hor}{ln\_dynldf\_hor}. 
     119 
     120%% ================================================================================================= 
    93121\subsection{Slopes for tracer iso-neutral mixing} 
    94122\label{subsec:LDF_slp_iso} 
     
    97125Their formulation does not depend on the vertical coordinate used. 
    98126Their discrete formulation is found using the fact that the diffusive fluxes of 
    99 locally referenced potential density (\ie $in situ$ density) vanish. 
    100 So, substituting $T$ by $\rho$ in \autoref{eq:tra_ldf_iso} and setting the diffusive fluxes in 
     127locally referenced potential density (\ie\ $in situ$ density) vanish. 
     128So, substituting $T$ by $\rho$ in \autoref{eq:TRA_ldf_iso} and setting the diffusive fluxes in 
    101129the three directions to zero leads to the following definition for the neutral slopes: 
    102130 
    103131\begin{equation} 
    104   \label{eq:ldfslp_iso} 
     132  \label{eq:LDF_slp_iso} 
    105133  \begin{split} 
    106134    r_{1u} &= \frac{e_{3u}}{e_{1u}}\; \frac{\delta_{i+1/2}[\rho]} 
     
    117145\end{equation} 
    118146 
    119 %gm% rewrite this as the explanation is not very clear !!! 
    120 %In practice, \autoref{eq:ldfslp_iso} is of little help in evaluating the neutral surface slopes. Indeed, for an unsimplified equation of state, the density has a strong dependancy on pressure (here approximated as the depth), therefore applying \autoref{eq:ldfslp_iso} using the $in situ$ density, $\rho$, computed at T-points leads to a flattening of slopes as the depth increases. This is due to the strong increase of the $in situ$ density with depth.  
    121  
    122 %By definition, neutral surfaces are tangent to the local $in situ$ density \citep{mcdougall_JPO87}, therefore in \autoref{eq:ldfslp_iso}, all the derivatives have to be evaluated at the same local pressure (which in decibars is approximated by the depth in meters). 
    123  
    124 %In the $z$-coordinate, the derivative of the  \autoref{eq:ldfslp_iso} numerator is evaluated at the same depth \nocite{as what?} ($T$-level, which is the same as the $u$- and $v$-levels), so  the $in situ$ density can be used for its evaluation.  
    125  
    126 As the mixing is performed along neutral surfaces, the gradient of $\rho$ in \autoref{eq:ldfslp_iso} has to 
     147\cmtgm{rewrite this as the explanation is not very clear !!!} 
     148%In practice, \autoref{eq:LDF_slp_iso} is of little help in evaluating the neutral surface slopes. Indeed, for an unsimplified equation of state, the density has a strong dependancy on pressure (here approximated as the depth), therefore applying \autoref{eq:LDF_slp_iso} using the $in situ$ density, $\rho$, computed at T-points leads to a flattening of slopes as the depth increases. This is due to the strong increase of the $in situ$ density with depth. 
     149 
     150%By definition, neutral surfaces are tangent to the local $in situ$ density \citep{mcdougall_JPO87}, therefore in \autoref{eq:LDF_slp_iso}, all the derivatives have to be evaluated at the same local pressure (which in decibars is approximated by the depth in meters). 
     151 
     152%In the $z$-coordinate, the derivative of the  \autoref{eq:LDF_slp_iso} numerator is evaluated at the same depth \nocite{as what?} ($T$-level, which is the same as the $u$- and $v$-levels), so  the $in situ$ density can be used for its evaluation. 
     153 
     154As the mixing is performed along neutral surfaces, the gradient of $\rho$ in \autoref{eq:LDF_slp_iso} has to 
    127155be evaluated at the same local pressure 
    128156(which, in decibars, is approximated by the depth in meters in the model). 
    129 Therefore \autoref{eq:ldfslp_iso} cannot be used as such, 
     157Therefore \autoref{eq:LDF_slp_iso} cannot be used as such, 
    130158but further transformation is needed depending on the vertical coordinate used: 
    131159 
    132160\begin{description} 
    133  
    134 \item[$z$-coordinate with full step: ] 
    135   in \autoref{eq:ldfslp_iso} the densities appearing in the $i$ and $j$ derivatives  are taken at the same depth, 
     161\item [$z$-coordinate with full step:] in \autoref{eq:LDF_slp_iso} the densities appearing in the $i$ and $j$ derivatives  are taken at the same depth, 
    136162  thus the $in situ$ density can be used. 
    137163  This is not the case for the vertical derivatives: $\delta_{k+1/2}[\rho]$ is replaced by $-\rho N^2/g$, 
    138164  where $N^2$ is the local Brunt-Vais\"{a}l\"{a} frequency evaluated following \citet{mcdougall_JPO87} 
    139   (see \autoref{subsec:TRA_bn2}).  
    140  
    141 \item[$z$-coordinate with partial step: ] 
    142   this case is identical to the full step case except that at partial step level, 
     165  (see \autoref{subsec:TRA_bn2}). 
     166\item [$z$-coordinate with partial step:] this case is identical to the full step case except that at partial step level, 
    143167  the \emph{horizontal} density gradient is evaluated as described in \autoref{sec:TRA_zpshde}. 
    144  
    145 \item[$s$- or hybrid $s$-$z$- coordinate: ] 
    146   in the current release of \NEMO, iso-neutral mixing is only employed for $s$-coordinates if 
    147   the Griffies scheme is used (\np{traldf\_grif}\forcode{ = .true.}; 
    148   see Appdx \autoref{apdx:triad}). 
     168\item [$s$- or hybrid $s$-$z$- coordinate:] in the current release of \NEMO, iso-neutral mixing is only employed for $s$-coordinates if 
     169  the Griffies scheme is used (\np[=.true.]{ln_traldf_triad}{ln\_traldf\_triad}; 
     170  see \autoref{apdx:TRIADS}). 
    149171  In other words, iso-neutral mixing will only be accurately represented with a linear equation of state 
    150   (\np{nn\_eos}\forcode{ = 1..2}). 
    151   In the case of a "true" equation of state, the evaluation of $i$ and $j$ derivatives in \autoref{eq:ldfslp_iso} 
     172  (\np[=.true.]{ln_seos}{ln\_seos}). 
     173  In the case of a "true" equation of state, the evaluation of $i$ and $j$ derivatives in \autoref{eq:LDF_slp_iso} 
    152174  will include a pressure dependent part, leading to the wrong evaluation of the neutral slopes. 
    153175 
    154 %gm%  
    155176  Note: The solution for $s$-coordinate passes trough the use of different (and better) expression for 
    156177  the constraint on iso-neutral fluxes. 
     
    161182    \alpha \ \textbf{F}(T) = \beta \ \textbf{F}(S) 
    162183  \] 
    163   % gm{  where vector F is ....} 
     184  \cmtgm{where vector F is ....} 
    164185 
    165186This constraint leads to the following definition for the slopes: 
    166187 
    167188\[ 
    168   % \label{eq:ldfslp_iso2} 
     189  % \label{eq:LDF_slp_iso2} 
    169190  \begin{split} 
    170191    r_{1u} &= \frac{e_{3u}}{e_{1u}}\; \frac 
     
    194215 
    195216Note that such a formulation could be also used in the $z$-coordinate and $z$-coordinate with partial steps cases. 
    196  
    197217\end{description} 
    198218 
    199219This implementation is a rather old one. 
    200 It is similar to the one proposed by Cox [1987], except for the background horizontal diffusion. 
    201 Indeed, the Cox implementation of isopycnal diffusion in GFDL-type models requires 
     220It is similar to the one proposed by \citet{cox_OM87}, except for the background horizontal diffusion. 
     221Indeed, the \citet{cox_OM87} implementation of isopycnal diffusion in GFDL-type models requires 
    202222a minimum background horizontal diffusion for numerical stability reasons. 
    203223To overcome this problem, several techniques have been proposed in which the numerical schemes of 
    204224the ocean model are modified \citep{weaver.eby_JPO97, griffies.gnanadesikan.ea_JPO98}. 
    205 Griffies's scheme is now available in \NEMO if \np{traldf\_grif\_iso} is set true; see Appdx \autoref{apdx:triad}. 
     225Griffies's scheme is now available in \NEMO\ if \np[=.true.]{ln_traldf_triad}{ln\_traldf\_triad}; see \autoref{apdx:TRIADS}. 
    206226Here, another strategy is presented \citep{lazar_phd97}: 
    207227a local filtering of the iso-neutral slopes (made on 9 grid-points) prevents the development of 
     
    209229This allows an iso-neutral diffusion scheme without additional background horizontal mixing. 
    210230This technique can be viewed as a diffusion operator that acts along large-scale 
    211 (2~$\Delta$x) \gmcomment{2deltax doesnt seem very large scale} iso-neutral surfaces. 
     231(2~$\Delta$x) \cmtgm{2deltax doesnt seem very large scale} iso-neutral surfaces. 
    212232The diapycnal diffusion required for numerical stability is thus minimized and its net effect on the flow is quite small when compared to the effect of an horizontal background mixing. 
    213233 
    214234Nevertheless, this iso-neutral operator does not ensure that variance cannot increase, 
    215 contrary to the \citet{griffies.gnanadesikan.ea_JPO98} operator which has that property.  
    216  
    217 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> 
     235contrary to the \citet{griffies.gnanadesikan.ea_JPO98} operator which has that property. 
     236 
    218237\begin{figure}[!ht] 
    219   \begin{center} 
    220     \includegraphics[width=\textwidth]{Fig_LDF_ZDF1} 
    221     \caption { 
    222       \protect\label{fig:LDF_ZDF1} 
    223       averaging procedure for isopycnal slope computation. 
    224     } 
    225   \end{center} 
     238  \centering 
     239  \includegraphics[width=0.66\textwidth]{LDF_ZDF1} 
     240  \caption{Averaging procedure for isopycnal slope computation} 
     241  \label{fig:LDF_ZDF1} 
    226242\end{figure} 
    227 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> 
    228  
    229 %There are three additional questions about the slope calculation.  
    230 %First the expression for the rotation tensor has been obtain assuming the "small slope" approximation, so a bound has to be imposed on slopes.  
    231 %Second, numerical stability issues also require a bound on slopes.  
     243 
     244%There are three additional questions about the slope calculation. 
     245%First the expression for the rotation tensor has been obtain assuming the "small slope" approximation, so a bound has to be imposed on slopes. 
     246%Second, numerical stability issues also require a bound on slopes. 
    232247%Third, the question of boundary condition specified on slopes... 
    233248 
    234249%from griffies: chapter 13.1.... 
    235250 
    236  
    237  
    238 % In addition and also for numerical stability reasons \citep{cox_OM87, griffies_bk04},  
    239 % the slopes are bounded by $1/100$ everywhere. This limit is decreasing linearly  
    240 % to zero fom $70$ meters depth and the surface (the fact that the eddies "feel" the  
     251% In addition and also for numerical stability reasons \citep{cox_OM87, griffies_bk04}, 
     252% the slopes are bounded by $1/100$ everywhere. This limit is decreasing linearly 
     253% to zero fom $70$ meters depth and the surface (the fact that the eddies "feel" the 
    241254% surface motivates this flattening of isopycnals near the surface). 
    242255 
    243256For numerical stability reasons \citep{cox_OM87, griffies_bk04}, the slopes must also be bounded by 
    244 $1/100$ everywhere. 
     257the namelist scalar \np{rn_slpmax}{rn\_slpmax} (usually $1/100$) everywhere. 
    245258This constraint is applied in a piecewise linear fashion, increasing from zero at the surface to 
    246259$1/100$ at $70$ metres and thereafter decreasing to zero at the bottom of the ocean 
    247260(the fact that the eddies "feel" the surface motivates this flattening of isopycnals near the surface). 
    248  
    249 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> 
     261\colorbox{yellow}{The way slopes are tapered has be checked. Not sure that this is still what is actually done.} 
     262 
    250263\begin{figure}[!ht] 
    251   \begin{center} 
    252     \includegraphics[width=\textwidth]{Fig_eiv_slp} 
    253     \caption{ 
    254       \protect\label{fig:eiv_slp} 
    255       Vertical profile of the slope used for lateral mixing in the mixed layer: 
    256       \textit{(a)} in the real ocean the slope is the iso-neutral slope in the ocean interior, 
    257       which has to be adjusted at the surface boundary 
    258       \ie it must tend to zero at the surface since there is no mixing across the air-sea interface: 
    259       wall boundary condition). 
    260       Nevertheless, the profile between the surface zero value and the interior iso-neutral one is unknown, 
    261       and especially the value at the base of the mixed layer; 
    262       \textit{(b)} profile of slope using a linear tapering of the slope near the surface and 
    263       imposing a maximum slope of 1/100; 
    264       \textit{(c)} profile of slope actually used in \NEMO: a linear decrease of the slope from 
    265       zero at the surface to its ocean interior value computed just below the mixed layer. 
    266       Note the huge change in the slope at the base of the mixed layer between \textit{(b)} and \textit{(c)}. 
    267     } 
    268   \end{center} 
     264  \centering 
     265  \includegraphics[width=0.66\textwidth]{LDF_eiv_slp} 
     266  \caption[Vertical profile of the slope used for lateral mixing in the mixed layer]{ 
     267    Vertical profile of the slope used for lateral mixing in the mixed layer: 
     268    \textit{(a)} in the real ocean the slope is the iso-neutral slope in the ocean interior, 
     269    which has to be adjusted at the surface boundary 
     270    \ie\ it must tend to zero at the surface since there is no mixing across the air-sea interface: 
     271    wall boundary condition). 
     272    Nevertheless, 
     273    the profile between the surface zero value and the interior iso-neutral one is unknown, 
     274    and especially the value at the base of the mixed layer; 
     275    \textit{(b)} profile of slope using a linear tapering of the slope near the surface and 
     276    imposing a maximum slope of 1/100; 
     277    \textit{(c)} profile of slope actually used in \NEMO: 
     278    a linear decrease of the slope from zero at the surface to 
     279    its ocean interior value computed just below the mixed layer. 
     280    Note the huge change in the slope at the base of the mixed layer between 
     281    \textit{(b)} and \textit{(c)}.} 
     282  \label{fig:LDF_eiv_slp} 
    269283\end{figure} 
    270 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> 
    271284 
    272285\colorbox{yellow}{add here a discussion about the flattening of the slopes, vs tapering the coefficient.} 
    273286 
     287%% ================================================================================================= 
    274288\subsection{Slopes for momentum iso-neutral mixing} 
    275289 
    276290The iso-neutral diffusion operator on momentum is the same as the one used on tracers but 
    277291applied to each component of the velocity separately 
    278 (see \autoref{eq:dyn_ldf_iso} in section~\autoref{subsec:DYN_ldf_iso}). 
     292(see \autoref{eq:DYN_ldf_iso} in section~\autoref{subsec:DYN_ldf_iso}). 
    279293The slopes between the surface along which the diffusion operator acts and the surface of computation 
    280294($z$- or $s$-surfaces) are defined at $T$-, $f$-, and \textit{uw}- points for the $u$-component, and $T$-, $f$- and 
    281295\textit{vw}- points for the $v$-component. 
    282296They are computed from the slopes used for tracer diffusion, 
    283 \ie \autoref{eq:ldfslp_geo} and \autoref{eq:ldfslp_iso}: 
     297\ie\ \autoref{eq:LDF_slp_geo} and \autoref{eq:LDF_slp_iso}: 
    284298 
    285299\[ 
    286   % \label{eq:ldfslp_dyn} 
     300  % \label{eq:LDF_slp_dyn} 
    287301  \begin{aligned} 
    288302    &r_{1t}\ \ = \overline{r_{1u}}^{\,i}       &&&    r_{1f}\ \ &= \overline{r_{1u}}^{\,i+1/2} \\ 
     
    295309The major issue remaining is in the specification of the boundary conditions. 
    296310The same boundary conditions are chosen as those used for lateral diffusion along model level surfaces, 
    297 \ie using the shear computed along the model levels and with no additional friction at the ocean bottom 
     311\ie\ using the shear computed along the model levels and with no additional friction at the ocean bottom 
    298312(see \autoref{sec:LBC_coast}). 
    299313 
    300  
    301 % ================================================================ 
    302 % Lateral Mixing Operator 
    303 % ================================================================ 
    304 \section[Lateral mixing operators (\textit{traldf.F90})] 
    305 {Lateral mixing operators (\protect\mdl{traldf}, \protect\mdl{traldf})} 
    306 \label{sec:LDF_op} 
    307  
    308  
    309     
    310 % ================================================================ 
    311 % Lateral Mixing Coefficients 
    312 % ================================================================ 
    313 \section[Lateral mixing coefficient (\textit{ldftra.F90}, \textit{ldfdyn.F90})] 
    314 {Lateral mixing coefficient (\protect\mdl{ldftra}, \protect\mdl{ldfdyn})} 
     314%% ================================================================================================= 
     315\section[Lateral mixing coefficient (\forcode{nn_aht_ijk_t} \& \forcode{nn_ahm_ijk_t})]{Lateral mixing coefficient (\protect\np{nn_aht_ijk_t}{nn\_aht\_ijk\_t} \& \protect\np{nn_ahm_ijk_t}{nn\_ahm\_ijk\_t})} 
    315316\label{sec:LDF_coef} 
    316317 
    317 Introducing a space variation in the lateral eddy mixing coefficients changes the model core memory requirement, 
    318 adding up to four extra three-dimensional arrays for the geopotential or isopycnal second order operator applied to  
    319 momentum. 
    320 Six CPP keys control the space variation of eddy coefficients: three for momentum and three for tracer. 
    321 The three choices allow: 
    322 a space variation in the three space directions (\key{traldf\_c3d},  \key{dynldf\_c3d}), 
    323 in the horizontal plane (\key{traldf\_c2d},  \key{dynldf\_c2d}), 
    324 or in the vertical only (\key{traldf\_c1d},  \key{dynldf\_c1d}). 
    325 The default option is a constant value over the whole ocean on both momentum and tracers.  
    326     
    327 The number of additional arrays that have to be defined and the gridpoint position at which 
    328 they are defined depend on both the space variation chosen and the type of operator used. 
    329 The resulting eddy viscosity and diffusivity coefficients can be a function of more than one variable. 
    330 Changes in the computer code when switching from one option to another have been minimized by 
    331 introducing the eddy coefficients as statement functions 
    332 (include file \textit{ldftra\_substitute.h90} and \textit{ldfdyn\_substitute.h90}). 
    333 The functions are replaced by their actual meaning during the preprocessing step (CPP). 
    334 The specification of the space variation of the coefficient is made in \mdl{ldftra} and \mdl{ldfdyn}, 
    335 or more precisely in include files \textit{traldf\_cNd.h90} and \textit{dynldf\_cNd.h90}, with N=1, 2 or 3. 
    336 The user can modify these include files as he/she wishes. 
    337 The way the mixing coefficient are set in the reference version can be briefly described as follows: 
    338  
    339 \subsubsection{Constant mixing coefficients (default option)} 
    340 When none of the \key{dynldf\_...} and \key{traldf\_...} keys are defined, 
    341 a constant value is used over the whole ocean for momentum and tracers, 
    342 which is specified through the \np{rn\_ahm0} and \np{rn\_aht0} namelist parameters. 
    343  
    344 \subsubsection[Vertically varying mixing coefficients (\texttt{\textbf{key\_traldf\_c1d}} and \texttt{\textbf{key\_dynldf\_c1d}})] 
    345 {Vertically varying mixing coefficients (\protect\key{traldf\_c1d} and \key{dynldf\_c1d})} 
    346 The 1D option is only available when using the $z$-coordinate with full step. 
    347 Indeed in all the other types of vertical coordinate, 
    348 the depth is a 3D function of (\textbf{i},\textbf{j},\textbf{k}) and therefore, 
    349 introducing depth-dependent mixing coefficients will require 3D arrays. 
    350 In the 1D option, a hyperbolic variation of the lateral mixing coefficient is introduced in which 
    351 the surface value is \np{rn\_aht0} (\np{rn\_ahm0}), the bottom value is 1/4 of the surface value, 
    352 and the transition takes place around z=300~m with a width of 300~m 
    353 (\ie both the depth and the width of the inflection point are set to 300~m). 
    354 This profile is hard coded in file \textit{traldf\_c1d.h90}, but can be easily modified by users. 
    355  
    356 \subsubsection[Horizontally varying mixing coefficients (\texttt{\textbf{key\_traldf\_c2d}} and \texttt{\textbf{key\_dynldf\_c2d}})] 
    357 {Horizontally varying mixing coefficients (\protect\key{traldf\_c2d} and \protect\key{dynldf\_c2d})} 
    358 By default the horizontal variation of the eddy coefficient depends on the local mesh size and 
     318The specification of the space variation of the coefficient is made in modules \mdl{ldftra} and \mdl{ldfdyn}. 
     319The way the mixing coefficients are set in the reference version can be described as follows: 
     320 
     321%% ================================================================================================= 
     322\subsection[Mixing coefficients read from file (\forcode{=-20, -30})]{ Mixing coefficients read from file (\protect\np[=-20, -30]{nn_aht_ijk_t}{nn\_aht\_ijk\_t} \& \protect\np[=-20, -30]{nn_ahm_ijk_t}{nn\_ahm\_ijk\_t})} 
     323 
     324Mixing coefficients can be read from file if a particular geographical variation is needed. For example, in the ORCA2 global ocean model, 
     325the laplacian viscosity operator uses $A^l$~= 4.10$^4$ m$^2$/s poleward of 20$^{\circ}$ north and south and 
     326decreases linearly to $A^l$~= 2.10$^3$ m$^2$/s at the equator \citep{madec.delecluse.ea_JPO96, delecluse.madec_icol99}. 
     327Similar modified horizontal variations can be found with the Antarctic or Arctic sub-domain options of ORCA2 and ORCA05. 
     328The provided fields can either be 2d (\np[=-20]{nn_aht_ijk_t}{nn\_aht\_ijk\_t}, \np[=-20]{nn_ahm_ijk_t}{nn\_ahm\_ijk\_t}) or 3d (\np[=-30]{nn_aht_ijk_t}{nn\_aht\_ijk\_t},  \np[=-30]{nn_ahm_ijk_t}{nn\_ahm\_ijk\_t}). They must be given at U, V points for tracers and T, F points for momentum (see \autoref{tab:LDF_files}). 
     329 
     330\begin{table}[htb] 
     331  \centering 
     332  \begin{tabular}{|l|l|l|l|} 
     333    \hline 
     334    Namelist parameter                       & Input filename                               & dimensions & variable names                      \\  \hline 
     335    \np[=-20]{nn_ahm_ijk_t}{nn\_ahm\_ijk\_t}     & \forcode{eddy_viscosity_2D.nc }            &     $(i,j)$         & \forcode{ahmt_2d, ahmf_2d}  \\  \hline 
     336    \np[=-20]{nn_aht_ijk_t}{nn\_aht\_ijk\_t}           & \forcode{eddy_diffusivity_2D.nc }           &     $(i,j)$           & \forcode{ahtu_2d, ahtv_2d}    \\   \hline 
     337    \np[=-30]{nn_ahm_ijk_t}{nn\_ahm\_ijk\_t}        & \forcode{eddy_viscosity_3D.nc }            &     $(i,j,k)$          & \forcode{ahmt_3d, ahmf_3d}  \\  \hline 
     338    \np[=-30]{nn_aht_ijk_t}{nn\_aht\_ijk\_t}     & \forcode{eddy_diffusivity_3D.nc }           &     $(i,j,k)$         & \forcode{ahtu_3d, ahtv_3d}    \\   \hline 
     339  \end{tabular} 
     340  \caption{Description of expected input files if mixing coefficients are read from NetCDF files} 
     341  \label{tab:LDF_files} 
     342\end{table} 
     343 
     344%% ================================================================================================= 
     345\subsection[Constant mixing coefficients (\forcode{=0})]{ Constant mixing coefficients (\protect\np[=0]{nn_aht_ijk_t}{nn\_aht\_ijk\_t} \& \protect\np[=0]{nn_ahm_ijk_t}{nn\_ahm\_ijk\_t})} 
     346 
     347If constant, mixing coefficients are set thanks to a velocity and a length scales ($U_{scl}$, $L_{scl}$) such that: 
     348 
     349\begin{equation} 
     350  \label{eq:LDF_constantah} 
     351  A_o^l = \left\{ 
     352    \begin{aligned} 
     353      & \frac{1}{2} U_{scl} L_{scl}            & \text{for laplacian operator } \\ 
     354      & \frac{1}{12} U_{scl} L_{scl}^3                    & \text{for bilaplacian operator } 
     355    \end{aligned} 
     356  \right. 
     357\end{equation} 
     358 
     359 $U_{scl}$ and $L_{scl}$ are given by the namelist parameters \np{rn_Ud}{rn\_Ud}, \np{rn_Uv}{rn\_Uv}, \np{rn_Ld}{rn\_Ld} and \np{rn_Lv}{rn\_Lv}. 
     360 
     361%% ================================================================================================= 
     362\subsection[Vertically varying mixing coefficients (\forcode{=10})]{Vertically varying mixing coefficients (\protect\np[=10]{nn_aht_ijk_t}{nn\_aht\_ijk\_t} \& \protect\np[=10]{nn_ahm_ijk_t}{nn\_ahm\_ijk\_t})} 
     363 
     364In the vertically varying case, a hyperbolic variation of the lateral mixing coefficient is introduced in which 
     365the surface value is given by \autoref{eq:LDF_constantah}, the bottom value is 1/4 of the surface value, 
     366and the transition takes place around z=500~m with a width of 200~m. 
     367This profile is hard coded in module \mdl{ldfc1d\_c2d}, but can be easily modified by users. 
     368 
     369%% ================================================================================================= 
     370\subsection[Mesh size dependent mixing coefficients (\forcode{=20})]{Mesh size dependent mixing coefficients (\protect\np[=20]{nn_aht_ijk_t}{nn\_aht\_ijk\_t} \& \protect\np[=20]{nn_ahm_ijk_t}{nn\_ahm\_ijk\_t})} 
     371 
     372In that case, the horizontal variation of the eddy coefficient depends on the local mesh size and 
    359373the type of operator used: 
    360374\begin{equation} 
    361   \label{eq:title} 
     375  \label{eq:LDF_title} 
    362376  A_l = \left\{ 
    363377    \begin{aligned} 
    364       & \frac{\max(e_1,e_2)}{e_{max}} A_o^l           & \text{for laplacian operator } \\ 
    365       & \frac{\max(e_1,e_2)^{3}}{e_{max}^{3}} A_o^l          & \text{for bilaplacian operator } 
     378      & \frac{1}{2} U_{scl}  \max(e_1,e_2)         & \text{for laplacian operator } \\ 
     379      & \frac{1}{12} U_{scl}  \max(e_1,e_2)^{3}             & \text{for bilaplacian operator } 
    366380    \end{aligned} 
    367381  \right. 
    368382\end{equation} 
    369 where $e_{max}$ is the maximum of $e_1$ and $e_2$ taken over the whole masked ocean domain, 
    370 and $A_o^l$ is the \np{rn\_ahm0} (momentum) or \np{rn\_aht0} (tracer) namelist parameter. 
     383where $U_{scl}$ is a user defined velocity scale (\np{rn_Ud}{rn\_Ud}, \np{rn_Uv}{rn\_Uv}). 
    371384This variation is intended to reflect the lesser need for subgrid scale eddy mixing where 
    372385the grid size is smaller in the domain. 
    373386It was introduced in the context of the DYNAMO modelling project \citep{willebrand.barnier.ea_PO01}. 
    374 Note that such a grid scale dependance of mixing coefficients significantly increase the range of stability of 
    375 model configurations presenting large changes in grid pacing such as global ocean models. 
     387Note that such a grid scale dependance of mixing coefficients significantly increases the range of stability of 
     388model configurations presenting large changes in grid spacing such as global ocean models. 
    376389Indeed, in such a case, a constant mixing coefficient can lead to a blow up of the model due to 
    377 large coefficient compare to the smallest grid size (see \autoref{sec:STP_forward_imp}), 
     390large coefficient compare to the smallest grid size (see \autoref{sec:TD_forward_imp}), 
    378391especially when using a bilaplacian operator. 
    379392 
    380 Other formulations can be introduced by the user for a given configuration. 
    381 For example, in the ORCA2 global ocean model (see Configurations), 
    382 the laplacian viscosity operator uses \np{rn\_ahm0}~= 4.10$^4$ m$^2$/s poleward of 20$^{\circ}$ north and south and 
    383 decreases linearly to \np{rn\_aht0}~= 2.10$^3$ m$^2$/s at the equator \citep{madec.delecluse.ea_JPO96, delecluse.madec_icol99}. 
    384 This modification can be found in routine \rou{ldf\_dyn\_c2d\_orca} defined in \mdl{ldfdyn\_c2d}. 
    385 Similar modified horizontal variations can be found with the Antarctic or Arctic sub-domain options of 
    386 ORCA2 and ORCA05 (see \&namcfg namelist). 
    387  
    388 \subsubsection[Space varying mixing coefficients (\texttt{\textbf{key\_traldf\_c3d}} and \texttt{\textbf{key\_dynldf\_c3d}})] 
    389 {Space varying mixing coefficients (\protect\key{traldf\_c3d} and \key{dynldf\_c3d})} 
    390  
    391 The 3D space variation of the mixing coefficient is simply the combination of the 1D and 2D cases, 
    392 \ie a hyperbolic tangent variation with depth associated with a grid size dependence of 
    393 the magnitude of the coefficient.  
    394  
    395 \subsubsection{Space and time varying mixing coefficients} 
    396  
    397 There is no default specification of space and time varying mixing coefficient.  
    398 The only case available is specific to the ORCA2 and ORCA05 global ocean configurations. 
    399 It provides only a tracer mixing coefficient for eddy induced velocity (ORCA2) or both iso-neutral and 
    400 eddy induced velocity (ORCA05) that depends on the local growth rate of baroclinic instability. 
    401 This specification is actually used when an ORCA key and both \key{traldf\_eiv} and \key{traldf\_c2d} are defined. 
     393\colorbox{yellow}{CASE \np{nn_aht_ijk_t}{nn\_aht\_ijk\_t} = 21 to be added} 
     394 
     395%% ================================================================================================= 
     396\subsection[Mesh size and depth dependent mixing coefficients (\forcode{=30})]{Mesh size and depth dependent mixing coefficients (\protect\np[=30]{nn_aht_ijk_t}{nn\_aht\_ijk\_t} \& \protect\np[=30]{nn_ahm_ijk_t}{nn\_ahm\_ijk\_t})} 
     397 
     398The 3D space variation of the mixing coefficient is simply the combination of the 1D and 2D cases above, 
     399\ie\ a hyperbolic tangent variation with depth associated with a grid size dependence of 
     400the magnitude of the coefficient. 
     401 
     402%% ================================================================================================= 
     403\subsection[Velocity dependent mixing coefficients (\forcode{=31})]{Flow dependent mixing coefficients (\protect\np[=31]{nn_aht_ijk_t}{nn\_aht\_ijk\_t} \& \protect\np[=31]{nn_ahm_ijk_t}{nn\_ahm\_ijk\_t})} 
     404In that case, the eddy coefficient is proportional to the local velocity magnitude so that the Reynolds number $Re =  \lvert U \rvert  e / A_l$ is constant (and here hardcoded to $12$): 
     405\colorbox{yellow}{JC comment: The Reynolds is effectively set to 12 in the code for both operators but shouldn't it be 2 for Laplacian ?} 
     406 
     407\begin{equation} 
     408  \label{eq:LDF_flowah} 
     409  A_l = \left\{ 
     410    \begin{aligned} 
     411      & \frac{1}{12} \lvert U \rvert e          & \text{for laplacian operator } \\ 
     412      & \frac{1}{12} \lvert U \rvert e^3             & \text{for bilaplacian operator } 
     413    \end{aligned} 
     414  \right. 
     415\end{equation} 
     416 
     417%% ================================================================================================= 
     418\subsection[Deformation rate dependent viscosities (\forcode{nn_ahm_ijk_t=32})]{Deformation rate dependent viscosities (\protect\np[=32]{nn_ahm_ijk_t}{nn\_ahm\_ijk\_t})} 
     419 
     420This option refers to the \citep{smagorinsky_MW63} scheme which is here implemented for momentum only. Smagorinsky chose as a 
     421characteristic time scale $T_{smag}$ the deformation rate and for the lengthscale $L_{smag}$ the maximum wavenumber possible on the horizontal grid, e.g.: 
     422 
     423\begin{equation} 
     424  \label{eq:LDF_smag1} 
     425  \begin{split} 
     426    T_{smag}^{-1} & = \sqrt{\left( \partial_x u - \partial_y v\right)^2 + \left( \partial_y u + \partial_x v\right)^2  } \\ 
     427    L_{smag} & = \frac{1}{\pi}\frac{e_1 e_2}{e_1 + e_2} 
     428  \end{split} 
     429\end{equation} 
     430 
     431Introducing a user defined constant $C$ (given in the namelist as \np{rn_csmc}{rn\_csmc}), one can deduce the mixing coefficients as follows: 
     432 
     433\begin{equation} 
     434  \label{eq:LDF_smag2} 
     435  A_{smag} = \left\{ 
     436    \begin{aligned} 
     437      & C^2  T_{smag}^{-1}  L_{smag}^2       & \text{for laplacian operator } \\ 
     438      & \frac{C^2}{8} T_{smag}^{-1} L_{smag}^4        & \text{for bilaplacian operator } 
     439    \end{aligned} 
     440  \right. 
     441\end{equation} 
     442 
     443For stability reasons, upper and lower limits are applied on the resulting coefficient (see \autoref{sec:TD_forward_imp}) so that: 
     444\begin{equation} 
     445  \label{eq:LDF_smag3} 
     446    \begin{aligned} 
     447      & C_{min} \frac{1}{2}   \lvert U \rvert  e    < A_{smag} < C_{max} \frac{e^2}{   8\rdt}                 & \text{for laplacian operator } \\ 
     448      & C_{min} \frac{1}{12} \lvert U \rvert  e^3 < A_{smag} < C_{max} \frac{e^4}{64 \rdt}                 & \text{for bilaplacian operator } 
     449    \end{aligned} 
     450\end{equation} 
     451 
     452where $C_{min}$ and $C_{max}$ are adimensional namelist parameters given by \np{rn_minfac}{rn\_minfac} and \np{rn_maxfac}{rn\_maxfac} respectively. 
     453 
     454%% ================================================================================================= 
     455\subsection{About space and time varying mixing coefficients} 
    402456 
    403457The following points are relevant when the eddy coefficient varies spatially: 
    404458 
    405459(1) the momentum diffusion operator acting along model level surfaces is written in terms of curl and 
    406 divergent components of the horizontal current (see \autoref{subsec:PE_ldf}). 
     460divergent components of the horizontal current (see \autoref{subsec:MB_ldf}). 
    407461Although the eddy coefficient could be set to different values in these two terms, 
    408 this option is not currently available.  
     462this option is not currently available. 
    409463 
    410464(2) with an horizontally varying viscosity, the quadratic integral constraints on enstrophy and on the square of 
    411465the horizontal divergence for operators acting along model-surfaces are no longer satisfied 
    412 (\autoref{sec:dynldf_properties}). 
    413  
    414 (3) for isopycnal diffusion on momentum or tracers, an additional purely horizontal background diffusion with 
    415 uniform coefficient can be added by setting a non zero value of \np{rn\_ahmb0} or \np{rn\_ahtb0}, 
    416 a background horizontal eddy viscosity or diffusivity coefficient 
    417 (namelist parameters whose default values are $0$). 
    418 However, the technique used to compute the isopycnal slopes is intended to get rid of such a background diffusion, 
    419 since it introduces spurious diapycnal diffusion (see \autoref{sec:LDF_slp}). 
    420  
    421 (4) when an eddy induced advection term is used (\key{traldf\_eiv}), 
    422 $A^{eiv}$, the eddy induced coefficient has to be defined. 
    423 Its space variations are controlled by the same CPP variable as for the eddy diffusivity coefficient 
    424 (\ie \key{traldf\_cNd}).  
    425  
    426 (5) the eddy coefficient associated with a biharmonic operator must be set to a \emph{negative} value. 
    427  
    428 (6) it is possible to use both the laplacian and biharmonic operators concurrently. 
    429  
    430 (7) it is possible to run without explicit lateral diffusion on momentum 
    431 (\np{ln\_dynldf\_lap}\forcode{ = .?.}\np{ln\_dynldf\_bilap}\forcode{ = .false.}). 
    432 This is recommended when using the UBS advection scheme on momentum (\np{ln\_dynadv\_ubs}\forcode{ = .true.}, 
    433 see \autoref{subsec:DYN_adv_ubs}) and can be useful for testing purposes. 
    434  
    435 % ================================================================ 
    436 % Eddy Induced Mixing 
    437 % ================================================================ 
    438 \section[Eddy induced velocity (\textit{traadv\_eiv.F90}, \textit{ldfeiv.F90})] 
    439 {Eddy induced velocity (\protect\mdl{traadv\_eiv}, \protect\mdl{ldfeiv})} 
     466(\autoref{sec:INVARIANTS_dynldf_properties}). 
     467 
     468%% ================================================================================================= 
     469\section[Eddy induced velocity (\forcode{ln_ldfeiv})]{Eddy induced velocity (\protect\np{ln_ldfeiv}{ln\_ldfeiv})} 
     470 
    440471\label{sec:LDF_eiv} 
    441472 
     473\begin{listing} 
     474  \nlst{namtra_eiv} 
     475  \caption{\forcode{&namtra_eiv}} 
     476  \label{lst:namtra_eiv} 
     477\end{listing} 
     478 
    442479%%gm  from Triad appendix  : to be incorporated.... 
    443 \gmcomment{ 
     480\cmtgm{ 
    444481  Values of iso-neutral diffusivity and GM coefficient are set as described in \autoref{sec:LDF_coef}. 
    445482  If none of the keys \key{traldf\_cNd}, N=1,2,3 is set (the default), spatially constant iso-neutral $A_l$ and 
    446   GM diffusivity $A_e$ are directly set by \np{rn\_aeih\_0} and \np{rn\_aeiv\_0}. 
     483  GM diffusivity $A_e$ are directly set by \np{rn_aeih_0}{rn\_aeih\_0} and \np{rn_aeiv_0}{rn\_aeiv\_0}. 
    447484  If 2D-varying coefficients are set with \key{traldf\_c2d} then $A_l$ is reduced in proportion with horizontal 
    448485  scale factor according to \autoref{eq:title} 
     
    457494    In this case, $A_e$ at low latitudes $|\theta|<20^{\circ}$ is further reduced by a factor $|f/f_{20}|$, 
    458495    where $f_{20}$ is the value of $f$ at $20^{\circ}$~N 
    459   } (\mdl{ldfeiv}) and \np{rn\_aeiv\_0} is ignored unless it is zero. 
     496  } (\mdl{ldfeiv}) and \np{rn_aeiv_0}{rn\_aeiv\_0} is ignored unless it is zero. 
    460497} 
    461498 
    462 When Gent and McWilliams [1990] diffusion is used (\key{traldf\_eiv} defined), 
     499When  \citet{gent.mcwilliams_JPO90} diffusion is used (\np[=.true.]{ln_ldfeiv}{ln\_ldfeiv}), 
    463500an eddy induced tracer advection term is added, 
    464501the formulation of which depends on the slopes of iso-neutral surfaces. 
    465502Contrary to the case of iso-neutral mixing, the slopes used here are referenced to the geopotential surfaces, 
    466 \ie \autoref{eq:ldfslp_geo} is used in $z$-coordinates, 
    467 and the sum \autoref{eq:ldfslp_geo} + \autoref{eq:ldfslp_iso} in $s$-coordinates. 
    468 The eddy induced velocity is given by:  
    469 \begin{equation} 
    470   \label{eq:ldfeiv} 
     503\ie\ \autoref{eq:LDF_slp_geo} is used in $z$-coordinates, 
     504and the sum \autoref{eq:LDF_slp_geo} + \autoref{eq:LDF_slp_iso} in $s$-coordinates. 
     505 
     506If isopycnal mixing is used in the standard way, \ie\ \np[=.false.]{ln_traldf_triad}{ln\_traldf\_triad}, the eddy induced velocity is given by: 
     507\begin{equation} 
     508  \label{eq:LDF_eiv} 
    471509  \begin{split} 
    472510    u^* & = \frac{1}{e_{2u}e_{3u}}\; \delta_k \left[e_{2u} \, A_{uw}^{eiv} \; \overline{r_{1w}}^{\,i+1/2} \right]\\ 
     
    475513  \end{split} 
    476514\end{equation} 
    477 where $A^{eiv}$ is the eddy induced velocity coefficient whose value is set through \np{rn\_aeiv}, 
    478 a \textit{nam\_traldf} namelist parameter. 
    479 The three components of the eddy induced velocity are computed and 
    480 add to the eulerian velocity in \mdl{traadv\_eiv}. 
     515where $A^{eiv}$ is the eddy induced velocity coefficient whose value is set through \np{nn_aei_ijk_t}{nn\_aei\_ijk\_t} \nam{tra_eiv}{tra\_eiv} namelist parameter. 
     516The three components of the eddy induced velocity are computed in \rou{ldf\_eiv\_trp} and 
     517added to the eulerian velocity in \rou{tra\_adv} where tracer advection is performed. 
    481518This has been preferred to a separate computation of the advective trends associated with the eiv velocity, 
    482519since it allows us to take advantage of all the advection schemes offered for the tracers 
     
    484521previous releases of OPA \citep{madec.delecluse.ea_NPM98}. 
    485522This is particularly useful for passive tracers where \emph{positivity} of the advection scheme is of 
    486 paramount importance.  
     523paramount importance. 
    487524 
    488525At the surface, lateral and bottom boundaries, the eddy induced velocity, 
    489 and thus the advective eddy fluxes of heat and salt, are set to zero.  
    490  
    491 \biblio 
    492  
    493 \pindex 
     526and thus the advective eddy fluxes of heat and salt, are set to zero. 
     527The value of the eddy induced mixing coefficient and its space variation is controlled in a similar way as for lateral mixing coefficient described in the preceding subsection (\np{nn_aei_ijk_t}{nn\_aei\_ijk\_t}, \np{rn_Ue}{rn\_Ue}, \np{rn_Le}{rn\_Le} namelist parameters). 
     528\colorbox{yellow}{CASE \np{nn_aei_ijk_t}{nn\_aei\_ijk\_t} = 21 to be added} 
     529 
     530In case of setting \np[=.true.]{ln_traldf_triad}{ln\_traldf\_triad}, a skew form of the eddy induced advective fluxes is used, which is described in \autoref{apdx:TRIADS}. 
     531 
     532%% ================================================================================================= 
     533\section[Mixed layer eddies (\forcode{ln_mle})]{Mixed layer eddies (\protect\np{ln_mle}{ln\_mle})} 
     534\label{sec:LDF_mle} 
     535 
     536\begin{listing} 
     537  \nlst{namtra_mle} 
     538  \caption{\forcode{&namtra_mle}} 
     539  \label{lst:namtra_mle} 
     540\end{listing} 
     541 
     542If  \np[=.true.]{ln_mle}{ln\_mle} in \nam{tra_mle}{tra\_mle} namelist, a parameterization of the mixing due to unresolved mixed layer instabilities is activated (\citet{foxkemper.ferrari_JPO08}). Additional transport is computed in \rou{ldf\_mle\_trp} and added to the eulerian transport in \rou{tra\_adv} as done for eddy induced advection. 
     543 
     544\colorbox{yellow}{TBC} 
     545 
     546\subinc{\input{../../global/epilogue}} 
    494547 
    495548\end{document} 
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