Changeset 10419 for NEMO/branches/2018/dev_r10164_HPC09_ESIWACE_PREP_MERGE/doc/latex/NEMO/subfiles/chap_model_basics_zstar.tex
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- 2018-12-19T20:46:30+01:00 (5 years ago)
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NEMO/branches/2018/dev_r10164_HPC09_ESIWACE_PREP_MERGE/doc/latex/NEMO/subfiles/chap_model_basics_zstar.tex
r10368 r10419 1 \documentclass[../tex_main/NEMO_manual]{subfiles} 1 \documentclass[../main/NEMO_manual]{subfiles} 2 2 3 \begin{document} 3 4 % ================================================================ 4 % Chapter 1 ———Model Basics5 % Chapter 1 Model Basics 5 6 % ================================================================ 6 7 % ================================================================ … … 20 21 21 22 \colorbox{yellow}{ end of to be updated} 22 \newline23 23 24 24 % from MOM4p1 documentation 25 25 26 26 To overcome problems with vanishing surface and/or bottom cells, we consider the zstar coordinate 27 \begin{equation} \label{eq:PE_} 28 z^\star = H \left( \frac{z-\eta}{H+\eta} \right) 29 \end{equation} 27 \[ 28 % \label{eq:PE_} 29 z^\star = H \left( \frac{z-\eta}{H+\eta} \right) 30 \] 30 31 31 32 This coordinate is closely related to the "eta" coordinate used in many atmospheric models … … 65 66 the surface height, again so long as $\eta > -H$. 66 67 67 68 69 68 %%% 70 69 % essai update time splitting... 71 70 %%% 72 71 73 74 72 % ================================================================ 75 73 % Surface Pressure Gradient and Sea Surface Height … … 79 77 %-----------------------------------------nam_dynspg---------------------------------------------------- 80 78 81 \nlst{nam_dynspg}79 %\nlst{nam_dynspg} 82 80 %------------------------------------------------------------------------------------------------------------ 83 81 Options are defined through the \ngn{nam\_dynspg} namelist variables. … … 105 103 describe the external gravity waves (typically a few ten seconds). 106 104 The sea surface height is given by: 107 \begin{equation} \label{eq:dynspg_ssh} 108 \frac{\partial \eta }{\partial t}\equiv \frac{\text{EMP}}{\rho _w }+\frac{1}{e_{1T} 109 e_{2T} }\sum\limits_k {\left( {\delta _i \left[ {e_{2u} e_{3u} u} 110 \right]+\delta _j \left[ {e_{1v} e_{3v} v} \right]} \right)} 105 \begin{equation} 106 \label{eq:dynspg_ssh} 107 \frac{\partial \eta }{\partial t}\equiv \frac{\text{EMP}}{\rho_w }+\frac{1}{e_{1T} 108 e_{2T} }\sum\limits_k {\left( {\delta_i \left[ {e_{2u} e_{3u} u} 109 \right]+\delta_j \left[ {e_{1v} e_{3v} v} \right]} \right)} 111 110 \end{equation} 112 111 113 112 where EMP is the surface freshwater budget (evaporation minus precipitation, and minus river runoffs 114 113 (if the later are introduced as a surface freshwater flux, see \autoref{chap:SBC}) expressed in $Kg.m^{-2}.s^{-1}$, 115 and $\rho 114 and $\rho_w =1,000\,Kg.m^{-3}$ is the volumic mass of pure water. 116 115 The sea-surface height is evaluated using a leapfrog scheme in combination with an Asselin time filter, 117 116 i.e. the velocity appearing in (\autoref{eq:dynspg_ssh}) is centred in time (\textit{now} velocity). 118 117 119 118 The surface pressure gradient, also evaluated using a leap-frog scheme, is then simply given by: 120 \begin{equation} \label{eq:dynspg_exp} 121 \left\{ \begin{aligned} 122 - \frac{1} {e_{1u}} \; \delta _{i+1/2} \left[ \,\eta\, \right] \\ 123 \\ 124 - \frac{1} {e_{2v}} \; \delta _{j+1/2} \left[ \,\eta\, \right] 125 \end{aligned} \right. 119 \begin{equation} 120 \label{eq:dynspg_exp} 121 \left\{ 122 \begin{aligned} 123 - \frac{1} {e_{1u}} \; \delta_{i+1/2} \left[ \,\eta\, \right] \\ \\ 124 - \frac{1} {e_{2v}} \; \delta_{j+1/2} \left[ \,\eta\, \right] 125 \end{aligned} 126 \right. 126 127 \end{equation} 127 128 128 Consistent with the linearization, a $\left. \rho \right|_{k=1} / \rho 129 Consistent with the linearization, a $\left. \rho \right|_{k=1} / \rho_o$ factor is omitted in 129 130 (\autoref{eq:dynspg_exp}). 130 131 … … 144 145 145 146 %> > > > > > > > > > > > > > > > > > > > > > > > > > > > 146 \begin{figure}[!t] \begin{center} 147 \includegraphics[width=0.90\textwidth]{Fig_DYN_dynspg_ts} 148 \caption{ \protect\label{fig:DYN_dynspg_ts} 149 Schematic of the split-explicit time stepping scheme for the barotropic and baroclinic modes, 150 after \citet{Griffies2004}. 151 Time increases to the right. 152 Baroclinic time steps are denoted by $t-\Delta t$, $t, t+\Delta t$, and $t+2\Delta t$. 153 The curved line represents a leap-frog time step, 154 and the smaller barotropic time steps $N \Delta t=2\Delta t$ are denoted by the zig-zag line. 155 The vertically integrated forcing \textbf{M}(t) computed at 156 baroclinic time step t represents the interaction between the barotropic and baroclinic motions. 157 While keeping the total depth, tracer, and freshwater forcing fields fixed, 158 a leap-frog integration carries the surface height and vertically integrated velocity from 159 t to $t+2 \Delta t$ using N barotropic time steps of length $\Delta t$. 160 Time averaging the barotropic fields over the N+1 time steps (endpoints included) 161 centers the vertically integrated velocity at the baroclinic timestep $t+\Delta t$. 162 A baroclinic leap-frog time step carries the surface height to $t+\Delta t$ using the convergence of 163 the time averaged vertically integrated velocity taken from baroclinic time step t. } 164 \end{center} 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 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 the convergence of 166 the time averaged vertically integrated velocity taken from baroclinic time step t. 167 } 168 \end{center} 165 169 \end{figure} 166 170 %> > > > > > > > > > > > > > > > > > > > > > > > > > > > … … 178 182 the small barotropic time step $\Delta t$. 179 183 We have 180 \begin{equation} \label{eq:DYN_spg_ts_eta} 181 \eta^{(b)}(\tau,t_{n+1}) - \eta^{(b)}(\tau,t_{n+1}) (\tau,t_{n-1}) 182 = 2 \Delta t \left[-\nabla \cdot \textbf{U}^{(b)}(\tau,t_n) + \text{EMP}_w(\tau) \right] 183 \end{equation} 184 \begin{multline} \label{eq:DYN_spg_ts_u} 185 \textbf{U}^{(b)}(\tau,t_{n+1}) - \textbf{U}^{(b)}(\tau,t_{n-1}) \\ 186 = 2\Delta t \left[ - f \textbf{k} \times \textbf{U}^{(b)}(\tau,t_{n}) 187 - H(\tau) \nabla p_s^{(b)}(\tau,t_{n}) +\textbf{M}(\tau) \right] 188 \end{multline} 184 \[ 185 % \label{eq:DYN_spg_ts_eta} 186 \eta^{(b)}(\tau,t_{n+1}) - \eta^{(b)}(\tau,t_{n+1}) (\tau,t_{n-1}) 187 = 2 \Delta t \left[-\nabla \cdot \textbf{U}^{(b)}(\tau,t_n) + \text{EMP}_w(\tau) \right] 188 \] 189 \begin{multline*} 190 % \label{eq:DYN_spg_ts_u} 191 \textbf{U}^{(b)}(\tau,t_{n+1}) - \textbf{U}^{(b)}(\tau,t_{n-1}) \\ 192 = 2\Delta t \left[ - f \textbf{k} \times \textbf{U}^{(b)}(\tau,t_{n}) 193 - H(\tau) \nabla p_s^{(b)}(\tau,t_{n}) +\textbf{M}(\tau) \right] 194 \end{multline*} 189 195 \ 190 196 … … 197 203 the duration of the barotropic time stepping over a single cycle. 198 204 This is also the time that sets the barotropic time steps via 199 \begin{equation} \label{eq:DYN_spg_ts_t} 200 t_n=\tau+n\Delta t 201 \end{equation} 205 \[ 206 % \label{eq:DYN_spg_ts_t} 207 t_n=\tau+n\Delta t 208 \] 202 209 with $n$ an integer. 203 210 The density scaled surface pressure is evaluated via 204 \begin{equation} \label{eq:DYN_spg_ts_ps} 205 p_s^{(b)}(\tau,t_{n}) = \begin{cases} 206 g \;\eta_s^{(b)}(\tau,t_{n}) \;\rho(\tau)_{k=1}) / \rho_o & \text{non-linear case} \\ 207 g \;\eta_s^{(b)}(\tau,t_{n}) & \text{linear case} 208 \end{cases} 209 \end{equation} 211 \[ 212 % \label{eq:DYN_spg_ts_ps} 213 p_s^{(b)}(\tau,t_{n}) = 214 \begin{cases} 215 g \;\eta_s^{(b)}(\tau,t_{n}) \;\rho(\tau)_{k=1}) / \rho_o & \text{non-linear case} \\ 216 g \;\eta_s^{(b)}(\tau,t_{n}) & \text{linear case} 217 \end{cases} 218 \] 210 219 To get started, we assume the following initial conditions 211 \ begin{equation} \label{eq:DYN_spg_ts_eta}212 \begin{split}213 \eta^{(b)}(\tau,t_{n=0}) &= \overline{\eta^{(b)}(\tau)}214 \\215 \eta^{(b)}(\tau,t_{n=1}) &= \eta^{(b)}(\tau,t_{n=0}) + \Delta t \ \text{RHS}_{n=0} 216 \end{split}217 \ end{equation}220 \[ 221 % \label{eq:DYN_spg_ts_eta} 222 \begin{split} 223 \eta^{(b)}(\tau,t_{n=0}) &= \overline{\eta^{(b)}(\tau)} \\ 224 \eta^{(b)}(\tau,t_{n=1}) &= \eta^{(b)}(\tau,t_{n=0}) + \Delta t \ \text{RHS}_{n=0} 225 \end{split} 226 \] 218 227 with 219 \begin{equation} \label{eq:DYN_spg_ts_etaF} 220 \overline{\eta^{(b)}(\tau)} = \frac{1}{N+1} \sum\limits_{n=0}^N \eta^{(b)}(\tau-\Delta t,t_{n}) 221 \end{equation} 228 \[ 229 % \label{eq:DYN_spg_ts_etaF} 230 \overline{\eta^{(b)}(\tau)} = \frac{1}{N+1} \sum\limits_{n=0}^N \eta^{(b)}(\tau-\Delta t,t_{n}) 231 \] 222 232 the time averaged surface height taken from the previous barotropic cycle. 223 233 Likewise, 224 \ begin{equation} \label{eq:DYN_spg_ts_u}225 \textbf{U}^{(b)}(\tau,t_{n=0}) = \overline{\textbf{U}^{(b)}(\tau)} \\ 226 \\227 \textbf{U}(\tau,t_{n=1}) = \textbf{U}^{(b)}(\tau,t_{n=0}) + \Delta t \ \text{RHS}_{n=0} 228 \ end{equation}234 \[ 235 % \label{eq:DYN_spg_ts_u} 236 \textbf{U}^{(b)}(\tau,t_{n=0}) = \overline{\textbf{U}^{(b)}(\tau)} \\ \\ 237 \textbf{U}(\tau,t_{n=1}) = \textbf{U}^{(b)}(\tau,t_{n=0}) + \Delta t \ \text{RHS}_{n=0} 238 \] 229 239 with 230 \ begin{equation} \label{eq:DYN_spg_ts_u}231 \overline{\textbf{U}^{(b)}(\tau)}232 233 \ end{equation}240 \[ 241 % \label{eq:DYN_spg_ts_u} 242 \overline{\textbf{U}^{(b)}(\tau)} = \frac{1}{N+1} \sum\limits_{n=0}^N\textbf{U}^{(b)}(\tau-\Delta t,t_{n}) 243 \] 234 244 the time averaged vertically integrated transport. 235 245 Notably, there is no Robert-Asselin time filter used in the barotropic portion of the integration. … … 237 247 Upon reaching $t_{n=N} = \tau + 2\Delta \tau$ , the vertically integrated velocity is time averaged to 238 248 produce the updated vertically integrated velocity at baroclinic time $\tau + \Delta \tau$ 239 \begin{equation} \label{eq:DYN_spg_ts_u} 240 \textbf{U}(\tau+\Delta t) = \overline{\textbf{U}^{(b)}(\tau+\Delta t)} 241 = \frac{1}{N+1} \sum\limits_{n=0}^N\textbf{U}^{(b)}(\tau,t_{n}) 242 \end{equation} 249 \[ 250 % \label{eq:DYN_spg_ts_u} 251 \textbf{U}(\tau+\Delta t) = \overline{\textbf{U}^{(b)}(\tau+\Delta t)} 252 = \frac{1}{N+1} \sum\limits_{n=0}^N\textbf{U}^{(b)}(\tau,t_{n}) 253 \] 243 254 The surface height on the new baroclinic time step is then determined via 244 255 a baroclinic leap-frog using the following form 245 \begin{equation} \label{eq:DYN_spg_ts_ssh} 246 \eta(\tau+\Delta) - \eta^{F}(\tau-\Delta) = 2\Delta t \ \left[ - \nabla \cdot \textbf{U}(\tau) + \text{EMP}_w \right] 256 \begin{equation} 257 \label{eq:DYN_spg_ts_ssh} 258 \eta(\tau+\Delta) - \eta^{F}(\tau-\Delta) = 2\Delta t \ \left[ - \nabla \cdot \textbf{U}(\tau) + \text{EMP}_w \right] 247 259 \end{equation} 248 260 … … 257 269 reasonably good maintenance of tracer conservation properties (see ??) 258 270 259 \begin{equation} \label{eq:DYN_spg_ts_sshf} 260 \eta^{F}(\tau-\Delta) = \overline{\eta^{(b)}(\tau)} 271 \begin{equation} 272 \label{eq:DYN_spg_ts_sshf} 273 \eta^{F}(\tau-\Delta) = \overline{\eta^{(b)}(\tau)} 261 274 \end{equation} 262 275 Another approach tried was 263 276 264 \begin{equation} \label{eq:DYN_spg_ts_sshf2} 265 \eta^{F}(\tau-\Delta) = \eta(\tau) 266 + (\alpha/2) \left[\overline{\eta^{(b)}}(\tau+\Delta t) 267 + \overline{\eta^{(b)}}(\tau-\Delta t) -2 \;\eta(\tau) \right] 268 \end{equation} 277 \[ 278 % \label{eq:DYN_spg_ts_sshf2} 279 \eta^{F}(\tau-\Delta) = \eta(\tau) 280 + (\alpha/2) \left[\overline{\eta^{(b)}}(\tau+\Delta t) 281 + \overline{\eta^{(b)}}(\tau-\Delta t) -2 \;\eta(\tau) \right] 282 \] 269 283 270 284 which is useful since it isolates all the time filtering aspects into the term multiplied by $\alpha$. … … 274 288 be more conservative, and so is recommended. 275 289 276 277 278 279 280 290 %------------------------------------------------------------- 281 291 % Filtered formulation … … 304 314 In particular, this means that in filtered case, the matrix to be inverted has to be recomputed at each time-step. 305 315 316 \biblio 306 317 307 318 \end{document}
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