Changeset 11831 for NEMO/branches/2019/dev_r11085_ASINTER-05_Brodeau_Advanced_Bulk/doc/latex/NEMO/subfiles/chap_model_basics_zstar.tex
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NEMO/branches/2019/dev_r11085_ASINTER-05_Brodeau_Advanced_Bulk/doc/latex/NEMO/subfiles/chap_model_basics_zstar.tex
r10544 r11831 2 2 3 3 \begin{document} 4 % ================================================================ 5 % Chapter 1 Model Basics 6 % ================================================================ 7 % ================================================================ 8 % Curvilinear \zstar- \sstar-coordinate System 9 % ================================================================ 4 10 5 \chapter{ essai \zstar \sstar} 6 7 \thispagestyle{plain} 8 9 \chaptertoc 10 11 \paragraph{Changes record} ~\\ 12 13 {\footnotesize 14 \begin{tabularx}{\textwidth}{l||X|X} 15 Release & Author(s) & Modifications \\ 16 \hline 17 {\em 4.0} & {\em ...} & {\em ...} \\ 18 {\em 3.6} & {\em ...} & {\em ...} \\ 19 {\em 3.4} & {\em ...} & {\em ...} \\ 20 {\em <=3.4} & {\em ...} & {\em ...} 21 \end{tabularx} 22 } 23 24 \clearpage 25 26 %% ================================================================================================= 11 27 \section{Curvilinear \zstar- or \sstar coordinate system} 12 28 13 % -------------------------------------------------------------------------------------------------------------14 % ????15 % -------------------------------------------------------------------------------------------------------------16 17 29 \colorbox{yellow}{ to be updated } 18 30 19 31 In that case, the free surface equation is nonlinear, and the variations of volume are fully taken into account. 20 These coordinates systems is presented in a report \citep{ Levier2007} available on the \NEMO web site.32 These coordinates systems is presented in a report \citep{levier.treguier.ea_rpt07} available on the \NEMO\ web site. 21 33 22 34 \colorbox{yellow}{ end of to be updated} … … 24 36 % from MOM4p1 documentation 25 37 26 To overcome problems with vanishing surface and/or bottom cells, we consider the zstar coordinate 27 \[ 28 % \label{eq: PE_}38 To overcome problems with vanishing surface and/or bottom cells, we consider the zstar coordinate 39 \[ 40 % \label{eq:MBZ_PE_} 29 41 z^\star = H \left( \frac{z-\eta}{H+\eta} \right) 30 42 \] … … 40 52 the surface height, it is clear that surfaces constant $z^\star$ are very similar to the depth surfaces. 41 53 These properties greatly reduce difficulties of computing the horizontal pressure gradient relative to 42 terrain following sigma models discussed in \autoref{subsec: PE_sco}.54 terrain following sigma models discussed in \autoref{subsec:MB_sco}. 43 55 Additionally, since $z^\star$ when $\eta = 0$, no flow is spontaneously generated in 44 56 an unforced ocean starting from rest, regardless the bottom topography. … … 49 61 neutral physics parameterizations in $z^\star$ models using the same techniques as in $z$-models 50 62 (see Chapters 13-16 of Griffies (2004) for a discussion of neutral physics in $z$-models, 51 as well as \autoref{sec:LDF_slp} in this document for treatment in \NEMO). 63 as well as \autoref{sec:LDF_slp} in this document for treatment in \NEMO). 52 64 53 65 The range over which $z^\star$ varies is time independent $-H \leq z^\star \leq 0$. 54 66 Hence, all cells remain nonvanishing, so long as the surface height maintains $\eta > ?H$. 55 This is a minor constraint relative to that encountered on the surface height when using $s = z$ or $s = z - \eta$. 67 This is a minor constraint relative to that encountered on the surface height when using $s = z$ or $s = z - \eta$. 56 68 57 69 Because $z^\star$ has a time independent range, all grid cells have static increments ds, 58 and the sum of the ver tical increments yields the time independent ocean depth %�k ds = H. 70 and the sum of the ver tical increments yields the time independent ocean depth %�k ds = H. 59 71 The $z^\star$ coordinate is therefore invisible to undulations of the free surface, 60 72 since it moves along with the free surface. … … 64 76 Quite generally, the time independent range for the $z^\star$ coordinate is a very convenient property that 65 77 allows for a nearly arbitrary vertical resolution even in the presence of large amplitude fluctuations of 66 the surface height, again so long as $\eta > -H$. 67 68 %%% 78 the surface height, again so long as $\eta > -H$. 79 69 80 % essai update time splitting... 70 %%% 71 72 % ================================================================ 73 % Surface Pressure Gradient and Sea Surface Height 74 % ================================================================ 75 \section{Surface pressure gradient and sea surface heigth (\protect\mdl{dynspg})} 76 \label{sec:DYN_hpg_spg} 77 %-----------------------------------------nam_dynspg---------------------------------------------------- 78 79 %\nlst{nam_dynspg} 80 %------------------------------------------------------------------------------------------------------------ 81 Options are defined through the \ngn{nam\_dynspg} namelist variables. 82 The surface pressure gradient term is related to the representation of the free surface (\autoref{sec:PE_hor_pg}). 81 82 %% ================================================================================================= 83 \section[Surface pressure gradient and sea surface heigth (\textit{dynspg.F90})]{Surface pressure gradient and sea surface heigth (\protect\mdl{dynspg})} 84 \label{sec:MBZ_dyn_hpg_spg} 85 86 %\nlst{nam_dynspg} 87 Options are defined through the \nam{_dynspg}{\_dynspg} namelist variables. 88 The surface pressure gradient term is related to the representation of the free surface (\autoref{sec:MB_hor_pg}). 83 89 The main distinction is between the fixed volume case (linear free surface or rigid lid) and 84 90 the variable volume case (nonlinear free surface, \key{vvl} is active). 85 In the linear free surface case (\autoref{subsec: PE_free_surface}) and rigid lid (\autoref{PE_rigid_lid}),91 In the linear free surface case (\autoref{subsec:MB_free_surface}) and rigid lid (\autoref{PE_rigid_lid}), 86 92 the vertical scale factors $e_{3}$ are fixed in time, 87 while in the nonlinear case (\autoref{subsec: PE_free_surface}) they are time-dependent.93 while in the nonlinear case (\autoref{subsec:MB_free_surface}) they are time-dependent. 88 94 With both linear and nonlinear free surface, external gravity waves are allowed in the equations, 89 95 which imposes a very small time step when an explicit time stepping is used. 90 96 Two methods are proposed to allow a longer time step for the three-dimensional equations: 91 the filtered free surface, which is a modification of the continuous equations %(see \autoref{eq: PE_flt}),97 the filtered free surface, which is a modification of the continuous equations %(see \autoref{eq:MB_flt?}), 92 98 and the split-explicit free surface described below. 93 99 The extra term introduced in the filtered method is calculated implicitly, 94 100 so that the update of the next velocities is done in module \mdl{dynspg\_flt} and not in \mdl{dynnxt}. 95 101 96 %-------------------------------------------------------------97 102 % Explicit 98 % -------------------------------------------------------------99 \subsubsection {Explicit (\protect\key{dynspg\_exp})}100 \label{subsec: DYN_spg_exp}103 %% ================================================================================================= 104 \subsubsection[Explicit (\texttt{\textbf{key\_dynspg\_exp}})]{Explicit (\protect\key{dynspg\_exp})} 105 \label{subsec:MBZ_dyn_spg_exp} 101 106 102 107 In the explicit free surface formulation, the model time step is chosen small enough to … … 104 109 The sea surface height is given by: 105 110 \begin{equation} 106 \label{eq: dynspg_ssh}111 \label{eq:MBZ_dynspg_ssh} 107 112 \frac{\partial \eta }{\partial t}\equiv \frac{\text{EMP}}{\rho_w }+\frac{1}{e_{1T} 108 113 e_{2T} }\sum\limits_k {\left( {\delta_i \left[ {e_{2u} e_{3u} u} … … 114 119 and $\rho_w =1,000\,Kg.m^{-3}$ is the volumic mass of pure water. 115 120 The sea-surface height is evaluated using a leapfrog scheme in combination with an Asselin time filter, 116 (\ie the velocity appearing in (\autoref{eq:dynspg_ssh}) is centred in time (\textit{now} velocity).121 (\ie\ the velocity appearing in (\autoref{eq:DYN_spg_ssh}) is centred in time (\textit{now} velocity). 117 122 118 123 The surface pressure gradient, also evaluated using a leap-frog scheme, is then simply given by: 119 124 \begin{equation} 120 \label{eq: dynspg_exp}125 \label{eq:MBZ_dynspg_exp} 121 126 \left\{ 122 127 \begin{aligned} … … 125 130 \end{aligned} 126 131 \right. 127 \end{equation} 132 \end{equation} 128 133 129 134 Consistent with the linearization, a $\left. \rho \right|_{k=1} / \rho_o$ factor is omitted in 130 (\autoref{eq:dynspg_exp}). 131 132 %------------------------------------------------------------- 135 (\autoref{eq:DYN_spg_exp}). 136 133 137 % Split-explicit time-stepping 134 %------------------------------------------------------------- 135 \subsubsection{Split-explicit time-stepping (\protect\key{dynspg\_ts})} 136 \label{subsec:DYN_spg_ts} 137 %--------------------------------------------namdom---------------------------------------------------- 138 139 \nlst{namdom} 140 %-------------------------------------------------------------------------------------------------------------- 141 The split-explicit free surface formulation used in OPA follows the one proposed by \citet{Griffies2004}. 138 %% ================================================================================================= 139 \subsubsection[Split-explicit time-stepping (\texttt{\textbf{key\_dynspg\_ts}})]{Split-explicit time-stepping (\protect\key{dynspg\_ts})} 140 \label{subsec:MBZ_dyn_spg_ts} 141 142 The split-explicit free surface formulation used in OPA follows the one proposed by \citet{Griffies2004?}. 142 143 The general idea is to solve the free surface equation with a small time step, 143 144 while the three dimensional prognostic variables are solved with a longer time step that 144 is a multiple of \np{rdtbt} in the \ngn{namdom} namelist (Figure III.3). 145 146 %> > > > > > > > > > > > > > > > > > > > > > > > > > > > 145 is a multiple of \np{rdtbt}{rdtbt} in the \nam{dom}{dom} namelist (Figure III.3). 146 147 147 \begin{figure}[!t] 148 \ begin{center}149 \includegraphics[width=0.90\textwidth]{Fig_DYN_dynspg_ts}150 \caption{151 \protect\label{fig:DYN_dynspg_ts}152 153 after \citet{Griffies2004}.154 155 156 157 158 159 160 161 162 163 164 165 A baroclinic leap-frog time step carries the surface height to $t+\Delta t$ using the convergence of166 the time averaged vertically integrated velocity taken from baroclinic time step t.167 }168 \ end{center}148 \centering 149 %\includegraphics[width=0.66\textwidth]{MBZ_DYN_dynspg_ts} 150 \caption[Schematic of the split-explicit time stepping scheme for 151 the barotropic and baroclinic modes, after \citet{Griffies2004?}]{ 152 Schematic of the split-explicit time stepping scheme for the barotropic and baroclinic modes, 153 after \citet{Griffies2004?}. 154 Time increases to the right. 155 Baroclinic time steps are denoted by $t-\Delta t$, $t, t+\Delta t$, and $t+2\Delta t$. 156 The curved line represents a leap-frog time step, 157 and the smaller barotropic time steps $N \Delta t=2\Delta t$ are denoted by the zig-zag line. 158 The vertically integrated forcing \textbf{M}(t) computed at 159 baroclinic time step t represents the interaction between the barotropic and baroclinic motions. 160 While keeping the total depth, tracer, and freshwater forcing fields fixed, 161 a leap-frog integration carries the surface height and vertically integrated velocity from 162 t to $t+2 \Delta t$ using N barotropic time steps of length $\Delta t$. 163 Time averaging the barotropic fields over the N+1 time steps (endpoints included) 164 centers the vertically integrated velocity at the baroclinic timestep $t+\Delta t$. 165 A baroclinic leap-frog time step carries the surface height to $t+\Delta t$ using 166 the convergence of the time averaged vertically integrated velocity taken from 167 baroclinic time step t.} 168 \label{fig:MBZ_dyn_dynspg_ts} 169 169 \end{figure} 170 %> > > > > > > > > > > > > > > > > > > > > > > > > > > >171 170 172 171 The split-explicit formulation has a damping effect on external gravity waves, 173 which is weaker than the filtered free surface but still significant as shown by \citet{ Levier2007} in174 the case of an analytical barotropic Kelvin wave. 172 which is weaker than the filtered free surface but still significant as shown by \citet{levier.treguier.ea_rpt07} in 173 the case of an analytical barotropic Kelvin wave. 175 174 176 175 %from griffies book: ..... copy past ! … … 183 182 We have 184 183 \[ 185 % \label{eq: DYN_spg_ts_eta}184 % \label{eq:MBZ_dyn_spg_ts_eta} 186 185 \eta^{(b)}(\tau,t_{n+1}) - \eta^{(b)}(\tau,t_{n+1}) (\tau,t_{n-1}) 187 = 2 \Delta t \left[-\nabla \cdot \textbf{U}^{(b)}(\tau,t_n) + \text{EMP}_w(\tau) \right] 186 = 2 \Delta t \left[-\nabla \cdot \textbf{U}^{(b)}(\tau,t_n) + \text{EMP}_w(\tau) \right] 188 187 \] 189 188 \begin{multline*} 190 % \label{eq: DYN_spg_ts_u}189 % \label{eq:MBZ_dyn_spg_ts_u} 191 190 \textbf{U}^{(b)}(\tau,t_{n+1}) - \textbf{U}^{(b)}(\tau,t_{n-1}) \\ 192 191 = 2\Delta t \left[ - f \textbf{k} \times \textbf{U}^{(b)}(\tau,t_{n}) … … 202 201 the freshwater flux $\text{EMP}_w(\tau)$, and total depth of the ocean $H(\tau)$ are held for 203 202 the duration of the barotropic time stepping over a single cycle. 204 This is also the time that sets the barotropic time steps via 205 \[ 206 % \label{eq: DYN_spg_ts_t}207 t_n=\tau+n\Delta t 203 This is also the time that sets the barotropic time steps via 204 \[ 205 % \label{eq:MBZ_dyn_spg_ts_t} 206 t_n=\tau+n\Delta t 208 207 \] 209 208 with $n$ an integer. 210 The density scaled surface pressure is evaluated via 211 \[ 212 % \label{eq: DYN_spg_ts_ps}209 The density scaled surface pressure is evaluated via 210 \[ 211 % \label{eq:MBZ_dyn_spg_ts_ps} 213 212 p_s^{(b)}(\tau,t_{n}) = 214 213 \begin{cases} … … 217 216 \end{cases} 218 217 \] 219 To get started, we assume the following initial conditions 220 \[ 221 % \label{eq: DYN_spg_ts_eta}218 To get started, we assume the following initial conditions 219 \[ 220 % \label{eq:MBZ_dyn_spg_ts_eta} 222 221 \begin{split} 223 222 \eta^{(b)}(\tau,t_{n=0}) &= \overline{\eta^{(b)}(\tau)} \\ … … 225 224 \end{split} 226 225 \] 227 with 228 \[ 229 % \label{eq: DYN_spg_ts_etaF}226 with 227 \[ 228 % \label{eq:MBZ_dyn_spg_ts_etaF} 230 229 \overline{\eta^{(b)}(\tau)} = \frac{1}{N+1} \sum\limits_{n=0}^N \eta^{(b)}(\tau-\Delta t,t_{n}) 231 230 \] … … 233 232 Likewise, 234 233 \[ 235 % \label{eq: DYN_spg_ts_u}234 % \label{eq:MBZ_dyn_spg_ts_u} 236 235 \textbf{U}^{(b)}(\tau,t_{n=0}) = \overline{\textbf{U}^{(b)}(\tau)} \\ \\ 237 236 \textbf{U}(\tau,t_{n=1}) = \textbf{U}^{(b)}(\tau,t_{n=0}) + \Delta t \ \text{RHS}_{n=0} 238 237 \] 239 with 240 \[ 241 % \label{eq: DYN_spg_ts_u}238 with 239 \[ 240 % \label{eq:MBZ_dyn_spg_ts_u} 242 241 \overline{\textbf{U}^{(b)}(\tau)} = \frac{1}{N+1} \sum\limits_{n=0}^N\textbf{U}^{(b)}(\tau-\Delta t,t_{n}) 243 242 \] 244 243 the time averaged vertically integrated transport. 245 Notably, there is no Robert-Asselin time filter used in the barotropic portion of the integration. 244 Notably, there is no Robert-Asselin time filter used in the barotropic portion of the integration. 246 245 247 246 Upon reaching $t_{n=N} = \tau + 2\Delta \tau$ , the vertically integrated velocity is time averaged to 248 produce the updated vertically integrated velocity at baroclinic time $\tau + \Delta \tau$ 249 \[ 250 % \label{eq: DYN_spg_ts_u}247 produce the updated vertically integrated velocity at baroclinic time $\tau + \Delta \tau$ 248 \[ 249 % \label{eq:MBZ_dyn_spg_ts_u} 251 250 \textbf{U}(\tau+\Delta t) = \overline{\textbf{U}^{(b)}(\tau+\Delta t)} 252 251 = \frac{1}{N+1} \sum\limits_{n=0}^N\textbf{U}^{(b)}(\tau,t_{n}) 253 252 \] 254 253 The surface height on the new baroclinic time step is then determined via 255 a baroclinic leap-frog using the following form 254 a baroclinic leap-frog using the following form 256 255 \begin{equation} 257 \label{eq: DYN_spg_ts_ssh}256 \label{eq:MBZ_dyn_spg_ts_ssh} 258 257 \eta(\tau+\Delta) - \eta^{F}(\tau-\Delta) = 2\Delta t \ \left[ - \nabla \cdot \textbf{U}(\tau) + \text{EMP}_w \right] 259 258 \end{equation} … … 261 260 The use of this "big-leap-frog" scheme for the surface height ensures compatibility between 262 261 the mass/volume budgets and the tracer budgets. 263 More discussion of this point is provided in Chapter 10 (see in particular Section 10.2). 264 262 More discussion of this point is provided in Chapter 10 (see in particular Section 10.2). 263 265 264 In general, some form of time filter is needed to maintain integrity of the surface height field due to 266 the leap-frog splitting mode in equation \autoref{eq: DYN_spg_ts_ssh}.265 the leap-frog splitting mode in equation \autoref{eq:MBZ_dyn_spg_ts_ssh}. 267 266 We have tried various forms of such filtering, 268 267 with the following method discussed in Griffies et al. (2001) chosen due to its stability and 269 reasonably good maintenance of tracer conservation properties (see ??) 268 reasonably good maintenance of tracer conservation properties (see ??) 270 269 271 270 \begin{equation} 272 \label{eq: DYN_spg_ts_sshf}271 \label{eq:MBZ_dyn_spg_ts_sshf} 273 272 \eta^{F}(\tau-\Delta) = \overline{\eta^{(b)}(\tau)} 274 273 \end{equation} 275 Another approach tried was 276 277 \[ 278 % \label{eq: DYN_spg_ts_sshf2}274 Another approach tried was 275 276 \[ 277 % \label{eq:MBZ_dyn_spg_ts_sshf2} 279 278 \eta^{F}(\tau-\Delta) = \eta(\tau) 280 279 + (\alpha/2) \left[\overline{\eta^{(b)}}(\tau+\Delta t) … … 285 284 This isolation allows for an easy check that tracer conservation is exact when eliminating tracer and 286 285 surface height time filtering (see ?? for more complete discussion). 287 However, in the general case with a non-zero $\alpha$, the filter \autoref{eq:DYN_spg_ts_sshf} was found to 288 be more conservative, and so is recommended. 289 290 %------------------------------------------------------------- 291 % Filtered formulation 292 %------------------------------------------------------------- 293 \subsubsection{Filtered formulation (\protect\key{dynspg\_flt})} 294 \label{subsec:DYN_spg_flt} 295 296 The filtered formulation follows the \citet{Roullet2000} implementation. 286 However, in the general case with a non-zero $\alpha$, the filter \autoref{eq:MBZ_dyn_spg_ts_sshf} was found to 287 be more conservative, and so is recommended. 288 289 % Filtered formulation 290 %% ================================================================================================= 291 \subsubsection[Filtered formulation (\texttt{\textbf{key\_dynspg\_flt}})]{Filtered formulation (\protect\key{dynspg\_flt})} 292 \label{subsec:MBZ_dyn_spg_flt} 293 294 The filtered formulation follows the \citet{Roullet2000?} implementation. 297 295 The extra term introduced in the equations (see {\S}I.2.2) is solved implicitly. 298 296 The elliptic solvers available in the code are documented in \autoref{chap:MISC}. 299 The amplitude of the extra term is given by the namelist variable \np{rnu}. 300 The default value is 1, as recommended by \citet{Roullet2000} 301 302 \colorbox{red}{\np{rnu}\forcode{ = 1} to be suppressed from namelist !} 303 304 %------------------------------------------------------------- 305 % Non-linear free surface formulation 306 %------------------------------------------------------------- 307 \subsection{Non-linear free surface formulation (\protect\key{vvl})} 308 \label{subsec:DYN_spg_vvl} 297 The amplitude of the extra term is given by the namelist variable \np{rnu}{rnu}. 298 The default value is 1, as recommended by \citet{Roullet2000?} 299 300 \colorbox{red}{\np[=1]{rnu}{rnu} to be suppressed from namelist !} 301 302 % Non-linear free surface formulation 303 %% ================================================================================================= 304 \subsection[Non-linear free surface formulation (\texttt{\textbf{key\_vvl}})]{Non-linear free surface formulation (\protect\key{vvl})} 305 \label{subsec:MBZ_dyn_spg_vvl} 309 306 310 307 In the non-linear free surface formulation, the variations of volume are fully taken into account. 311 This option is presented in a report \citep{ Levier2007} available on the NEMOweb site.308 This option is presented in a report \citep{levier.treguier.ea_rpt07} available on the \NEMO\ web site. 312 309 The three time-stepping methods (explicit, split-explicit and filtered) are the same as in 313 \autoref{ DYN_spg_linear} except that the ocean depth is now time-dependent.310 \autoref{?:DYN_spg_linear?} except that the ocean depth is now time-dependent. 314 311 In particular, this means that in filtered case, the matrix to be inverted has to be recomputed at each time-step. 315 312 316 \biblio 317 318 \pindex 313 \subinc{\input{../../global/epilogue}} 319 314 320 315 \end{document}
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