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1 % $Header: /u/gcmpack/manual/s_examples/global_oce_latlon/climatalogical_ogcm.tex,v 1.24 2013/05/15 22:47:12 jmc Exp $
2 % $Name: $
3
4 \section[Global Ocean MITgcm Example]{Global Ocean Simulation at $4^\circ$ Resolution}
5 %\label{www:tutorials}
6 \label{sec:eg-global}
7 \begin{rawhtml}
8 <!-- CMIREDIR:eg-global: -->
9 \end{rawhtml}
10 \begin{center}
11 (in directory: {\it verification/tutorial\_global\_oce\_latlon/})
12 \end{center}
13
14 \bodytext{bgcolor="#FFFFFFFF"}
15
16 \noindent {\bf WARNING: the description of this experiment is not complete.
17 In particular, many parameters are not yet described.}\\
18
19 %\begin{center}
20 %{\Large \bf Using MITgcm to Simulate Global Climatological Ocean Circulation
21 %At Four Degree Resolution with Asynchronous Time Stepping}
22 %
23 %\vspace*{4mm}
24 %
25 %\vspace*{3mm}
26 %{\large May 2001}
27 %\end{center}
28
29 This example experiment demonstrates using the MITgcm to simulate the
30 planetary ocean circulation. The simulation is configured with
31 realistic geography and bathymetry on a $4^{\circ} \times 4^{\circ}$
32 spherical polar grid. The files for this experiment are in the
33 verification directory under tutorial\_global\_oce\_latlon. Fifteen
34 levels are used in the vertical, ranging in thickness from $50\,{\rm
35 m}$ at the surface to $690\,{\rm m}$ at depth, giving a maximum
36 model depth of $5200\,{\rm m}$.
37 Different time-steps are used to accelerate the convergence to
38 equilibrium \cite[]{bryan:84} so that, at this resolution,
39 the configuration can be integrated forward for thousands of years
40 on a single processor desktop computer.
41 \\
42 \subsection{Overview}
43 %\label{www:tutorials}
44
45 The model is forced with climatological wind stress data from
46 \citet{trenberth90} and NCEP surface flux data from
47 \citet{kalnay96}. Climatological data \citep{Levitus94} is
48 used to initialize the model hydrography. \citeauthor{Levitus94} seasonal
49 climatology data is also used throughout the calculation to provide
50 additional air-sea fluxes. These fluxes are combined with the NCEP
51 climatological estimates of surface heat flux, resulting in a mixed
52 boundary condition of the style described in \citet{Haney}.
53 Altogether, this yields the following forcing applied in the model
54 surface layer.
55
56 \begin{eqnarray}
57 \label{eq:eg-global-global_forcing}
58 \label{eq:eg-global-global_forcing_fu}
59 {\cal F}_{u} & = & \frac{\tau_{x}}{\rho_{0} \Delta z_{s}}
60 \\
61 \label{eq:eg-global-global_forcing_fv}
62 {\cal F}_{v} & = & \frac{\tau_{y}}{\rho_{0} \Delta z_{s}}
63 \\
64 \label{eq:eg-global-global_forcing_ft}
65 {\cal F}_{\theta} & = & - \lambda_{\theta} ( \theta - \theta^{\ast} )
66 - \frac{1}{C_{p} \rho_{0} \Delta z_{s}}{\cal Q}
67 \\
68 \label{eq:eg-global-global_forcing_fs}
69 {\cal F}_{s} & = & - \lambda_{s} ( S - S^{\ast} )
70 + \frac{S_{0}}{\Delta z_{s}}({\cal E} - {\cal P} - {\cal R})
71 \end{eqnarray}
72
73 \noindent where ${\cal F}_{u}$, ${\cal F}_{v}$, ${\cal F}_{\theta}$,
74 ${\cal F}_{s}$ are the forcing terms in the zonal and meridional
75 momentum and in the potential temperature and salinity
76 equations respectively.
77 The term $\Delta z_{s}$ represents the top ocean layer thickness in
78 meters.
79 It is used in conjunction with a reference density, $\rho_{0}$
80 (here set to $999.8\,{\rm kg\,m^{-3}}$), a
81 reference salinity, $S_{0}$ (here set to 35~ppt),
82 and a specific heat capacity, $C_{p}$ (here set to
83 $4000~{\rm J}~^{\circ}{\rm C}^{-1}~{\rm kg}^{-1}$), to convert
84 input dataset values into time tendencies of
85 potential temperature (with units of $^{\circ}{\rm C}~{\rm s}^{-1}$),
86 salinity (with units ${\rm ppt}~s^{-1}$) and
87 velocity (with units ${\rm m}~{\rm s}^{-2}$).
88 The externally supplied forcing fields used in this
89 experiment are $\tau_{x}$, $\tau_{y}$, $\theta^{\ast}$, $S^{\ast}$,
90 $\cal{Q}$ and $\cal{E}-\cal{P}-\cal{R}$. The wind stress fields ($\tau_x$, $\tau_y$)
91 have units of ${\rm N}~{\rm m}^{-2}$. The temperature forcing fields
92 ($\theta^{\ast}$ and $Q$) have units of $^{\circ}{\rm C}$ and ${\rm W}~{\rm m}^{-2}$
93 respectively. The salinity forcing fields ($S^{\ast}$ and
94 $\cal{E}-\cal{P}-\cal{R}$) have units of ${\rm ppt}$ and ${\rm m}~{\rm s}^{-1}$
95 respectively. The source files and procedures for ingesting this data into the
96 simulation are described in the experiment configuration discussion in section
97 \ref{sec:eg-global-clim_ocn_examp_exp_config}.
98
99
100 \subsection{Discrete Numerical Configuration}
101 %\label{www:tutorials}
102
103
104 The model is configured in hydrostatic form. The domain is
105 discretised with a uniform grid spacing in latitude and longitude on
106 the sphere $\Delta \phi=\Delta \lambda=4^{\circ}$, so that there are
107 ninety grid cells in the zonal and forty in the meridional
108 direction. The internal model coordinate variables $x$ and $y$ are
109 initialized according to
110 \begin{eqnarray}
111 x=r\cos(\phi),~\Delta x & = &r\cos(\Delta \phi) \\
112 y=r\lambda,~\Delta y &= &r\Delta \lambda
113 \end{eqnarray}
114
115 Arctic polar regions are not
116 included in this experiment. Meridionally the model extends from
117 $80^{\circ}{\rm S}$ to $80^{\circ}{\rm N}$.
118 Vertically the model is configured with fifteen layers with the
119 following thicknesses:
120 $\Delta z_{1} = 50\,{\rm m},$\\
121 $\Delta z_{2} = 70\,{\rm m},\,
122 \Delta z_{3} = 100\,{\rm m},\,
123 \Delta z_{4} = 140\,{\rm m},\,
124 \Delta z_{5} = 190\,{\rm m},\,
125 \Delta z_{6} = 240\,{\rm m},\,
126 \Delta z_{7} = 290\,{\rm m},\,
127 \Delta z_{8} = 340\,{\rm m},$\\
128 $\Delta z_{9} = 390\,{\rm m},\,
129 \Delta z_{10}= 440\,{\rm m},\,
130 \Delta z_{11}= 490\,{\rm m},\,
131 \Delta z_{12}= 540\,{\rm m},\,
132 \Delta z_{13}= 590\,{\rm m},\,
133 \Delta z_{14}= 640\,{\rm m},\,
134 \Delta z_{15}= 690\,{\rm m}$\\
135 (here the numeric subscript indicates the model level index number, ${\tt k}$) to
136 give a total depth, $H$, of $-5200{\rm m}$.
137 The implicit free surface form of the pressure equation described in
138 \citet{marshall:97a} is employed. A Laplacian operator, $\nabla^2$, provides viscous
139 dissipation. Thermal and haline diffusion is also represented by a Laplacian operator.
140
141 Wind-stress forcing is added to the momentum equations in (\ref{eq:eg-global-model_equations})
142 for both the zonal flow, $u$ and the meridional flow $v$, according to equations
143 (\ref{eq:eg-global-global_forcing_fu}) and (\ref{eq:eg-global-global_forcing_fv}).
144 Thermodynamic forcing inputs are added to the equations
145 in (\ref{eq:eg-global-model_equations}) for
146 potential temperature, $\theta$, and salinity, $S$, according to equations
147 (\ref{eq:eg-global-global_forcing_ft}) and (\ref{eq:eg-global-global_forcing_fs}).
148 This produces a set of equations solved in this configuration as follows:
149
150 \begin{eqnarray}
151 \label{eq:eg-global-model_equations}
152 \frac{Du}{Dt} - fv +
153 \frac{1}{\rho}\frac{\partial p^{'}}{\partial x} -
154 \nabla_{h}\cdot A_{h}\nabla_{h}u -
155 \frac{\partial}{\partial z}A_{z}\frac{\partial u}{\partial z}
156 & = &
157 \begin{cases}
158 {\cal F}_u & \text{(surface)} \\
159 0 & \text{(interior)}
160 \end{cases}
161 \\
162 \frac{Dv}{Dt} + fu +
163 \frac{1}{\rho}\frac{\partial p^{'}}{\partial y} -
164 \nabla_{h}\cdot A_{h}\nabla_{h}v -
165 \frac{\partial}{\partial z}A_{z}\frac{\partial v}{\partial z}
166 & = &
167 \begin{cases}
168 {\cal F}_v & \text{(surface)} \\
169 0 & \text{(interior)}
170 \end{cases}
171 \\
172 \frac{\partial \eta}{\partial t} + \nabla_{h}\cdot \vec{u}
173 &=&
174 0
175 \\
176 \frac{D\theta}{Dt} -
177 \nabla_{h}\cdot K_{h}\nabla_{h}\theta
178 - \frac{\partial}{\partial z}\Gamma(K_{z})\frac{\partial\theta}{\partial z}
179 & = &
180 \begin{cases}
181 {\cal F}_\theta & \text{(surface)} \\
182 0 & \text{(interior)}
183 \end{cases}
184 \\
185 \frac{D s}{Dt} -
186 \nabla_{h}\cdot K_{h}\nabla_{h}s
187 - \frac{\partial}{\partial z}\Gamma(K_{z})\frac{\partial s}{\partial z}
188 & = &
189 \begin{cases}
190 {\cal F}_s & \text{(surface)} \\
191 0 & \text{(interior)}
192 \end{cases}
193 \\
194 g\rho_{0} \eta + \int^{0}_{-z}\rho^{'} dz & = & p^{'}
195 \end{eqnarray}
196
197 \noindent where $u=\frac{Dx}{Dt}=r \cos(\phi)\frac{D \lambda}{Dt}$ and
198 $v=\frac{Dy}{Dt}=r \frac{D \phi}{Dt}$
199 are the zonal and meridional components of the
200 flow vector, $\vec{u}$, on the sphere. As described in
201 MITgcm Numerical Solution Procedure \ref{chap:discretization}, the time
202 evolution of potential temperature, $\theta$, equation is solved prognostically.
203 The total pressure, $p$, is diagnosed by summing pressure due to surface
204 elevation $\eta$ and the hydrostatic pressure.
205 \\
206
207 \subsubsection{Numerical Stability Criteria}
208 %\label{www:tutorials}
209
210 The Laplacian dissipation coefficient, $A_{h}$, is set to $5 \times 10^5 m s^{-1}$.
211 This value is chosen to yield a Munk layer width \citep{adcroft:95},
212 \begin{eqnarray}
213 \label{eq:eg-global-munk_layer}
214 && M_{w} = \pi ( \frac { A_{h} }{ \beta } )^{\frac{1}{3}}
215 \end{eqnarray}
216
217 \noindent of $\approx 600$km. This is greater than the model
218 resolution in low-latitudes, $\Delta x \approx 400{\rm km}$, ensuring that the frictional
219 boundary layer is adequately resolved.
220 \\
221
222 \noindent The model is stepped forward with a time step $\Delta
223 t_{\theta}=24~{\rm hours}$ for thermodynamic variables and $\Delta
224 t_{v}=30~{\rm minutes}$ for momentum terms. With this time step,
225 the stability parameter to the horizontal Laplacian friction
226 \citep{adcroft:95}
227 \begin{eqnarray}
228 \label{eq:eg-global-laplacian_stability}
229 && S_{l} = 4 \frac{A_{h} \Delta t_{v}}{{\Delta x}^2}
230 \end{eqnarray}
231
232 \noindent evaluates to 0.6 at a latitude of $\phi=80^{\circ}$, which
233 is above the 0.3 upper limit for stability, but the zonal grid spacing
234 $\Delta x$ is smallest at $\phi=80^{\circ}$ where $\Delta
235 x=r\cos(\phi)\Delta \phi\approx 77{\rm km}$ and the stability
236 criterion is already met 1 grid cell equatorwards (at $\phi=76^{\circ}$).
237
238
239 \noindent The vertical dissipation coefficient, $A_{z}$, is set to
240 $1\times10^{-3} {\rm m}^2{\rm s}^{-1}$. The associated stability limit
241 \begin{eqnarray}
242 \label{eq:eg-global-laplacian_stability_z}
243 && S_{l} = 4 \frac{A_{z} \Delta t_{v}}{{\Delta z}^2}
244 \end{eqnarray}
245
246 \noindent evaluates to $0.0029$ for the smallest model
247 level spacing ($\Delta z_{1}=50{\rm m}$) which is well below
248 the upper stability limit.
249 \\
250
251 % The values of the horizontal ($K_{h}$) and vertical ($K_{z}$) diffusion coefficients
252 % for both temperature and salinity are set to $1 \times 10^{3}~{\rm m}^{2}{\rm s}^{-1}$
253 % and $3 \times 10^{-5}~{\rm m}^{2}{\rm s}^{-1}$ respectively. The stability limit
254 % related to $K_{h}$ will be at $\phi=80^{\circ}$ where $\Delta x \approx 77 {\rm km}$.
255 % Here the stability parameter
256 % \begin{eqnarray}
257 % \label{eq:eg-global-laplacian_stability_xtheta}
258 % S_{l} = \frac{4 K_{h} \Delta t_{\theta}}{{\Delta x}^2}
259 % \end{eqnarray}
260 % evaluates to $0.07$, well below the stability limit of $S_{l} \approx 0.5$. The
261 % stability parameter related to $K_{z}$
262 % \begin{eqnarray}
263 % \label{eq:eg-global-laplacian_stability_ztheta}
264 % S_{l} = \frac{4 K_{z} \Delta t_{\theta}}{{\Delta z}^2}
265 % \end{eqnarray}
266 % evaluates to $0.005$ for $\min(\Delta z)=50{\rm m}$, well below the stability limit
267 % of $S_{l} \approx 0.5$.
268 % \\
269
270 \noindent The numerical stability for inertial oscillations
271 \citep{adcroft:95}
272
273 \begin{eqnarray}
274 \label{eq:eg-global-inertial_stability}
275 && S_{i} = f^{2} {\Delta t_v}^2
276 \end{eqnarray}
277
278 \noindent evaluates to $0.07$ for
279 $f=2\omega\sin(80^{\circ})=1.43\times10^{-4}~{\rm s}^{-1}$, which is
280 below the $S_{i} < 1$ upper limit for stability.
281 \\
282
283 \noindent The advective CFL \citep{adcroft:95} for a extreme maximum
284 horizontal flow
285 speed of $ | \vec{u} | = 2 ms^{-1}$
286
287 \begin{eqnarray}
288 \label{eq:eg-global-cfl_stability}
289 && S_{a} = \frac{| \vec{u} | \Delta t_{v}}{ \Delta x}
290 \end{eqnarray}
291
292 \noindent evaluates to $5 \times 10^{-2}$. This is well below the stability
293 limit of 0.5.
294 \\
295
296 \noindent The stability parameter for internal gravity waves propagating
297 with a maximum speed of $c_{g}=10~{\rm ms}^{-1}$
298 \citep{adcroft:95}
299
300 \begin{eqnarray}
301 \label{eq:eg-global-gfl_stability}
302 && S_{c} = \frac{c_{g} \Delta t_{v}}{ \Delta x}
303 \end{eqnarray}
304
305 \noindent evaluates to $2.3 \times 10^{-1}$. This is close to the linear
306 stability limit of 0.5.
307
308 \subsection{Experiment Configuration}
309 %\label{www:tutorials}
310 \label{sec:eg-global-clim_ocn_examp_exp_config}
311
312 The model configuration for this experiment resides under the
313 directory {\it tutorial\_global\_oce\_latlon/}. The experiment files
314
315 \begin{itemize}
316 \item {\it input/data}
317 \item {\it input/data.pkg}
318 \item {\it input/eedata},
319 \item {\it input/trenberth\_taux.bin},
320 \item {\it input/trenberth\_tauy.bin},
321 \item {\it input/lev\_s.bin},
322 \item {\it input/lev\_t.bin},
323 \item {\it input/lev\_sss.bin},
324 \item {\it input/lev\_sst.bin},
325 \item {\it input/bathymetry.bin},
326 %\item {\it code/CPP\_EEOPTIONS.h}
327 %\item {\it code/CPP\_OPTIONS.h},
328 \item {\it code/SIZE.h}.
329 \end{itemize}
330 contain the code customizations and parameter settings for these
331 experiments. Below we describe the customizations
332 to these files associated with this experiment.
333
334 \subsubsection{Driving Datasets}
335 %\label{www:tutorials}
336
337 %% New figures are included before
338 %% Relaxation temperature
339 %\begin{figure}
340 %\centering
341 %\includegraphics[]{relax_temperature.eps}
342 %\caption{Relaxation temperature for January}
343 %\label{fig:relax_temperature}
344 %\end{figure}
345
346 %% Relaxation salinity
347 %\begin{figure}
348 %\centering
349 %\includegraphics[]{relax_salinity.eps}
350 %\caption{Relaxation salinity for January}
351 %\label{fig:relax_salinity}
352 %\end{figure}
353
354 %% tau_x
355 %\begin{figure}
356 %\centering
357 %\includegraphics[]{tau_x.eps}
358 %\caption{zonal wind stress for January}
359 %\label{fig:tau_x}
360 %\end{figure}
361
362 %% tau_y
363 %\begin{figure}
364 %\centering
365 %\includegraphics[]{tau_y.eps}
366 %\caption{meridional wind stress for January}
367 %\label{fig:tau_y}
368 %\end{figure}
369
370 %% Qnet
371 %\begin{figure}
372 %\centering
373 %\includegraphics[]{qnet.eps}
374 %\caption{Heat flux for January}
375 %\label{fig:qnet}
376 %\end{figure}
377
378 %% EmPmR
379 %\begin{figure}
380 %\centering
381 %\includegraphics[]{empmr.eps}
382 %\caption{Fresh water flux for January}
383 %\label{fig:empmr}
384 %\end{figure}
385
386 %% Bathymetry
387 %\begin{figure}
388 %\centering
389 %\includegraphics[]{bathymetry.eps}
390 %\caption{Bathymetry}
391 %\label{fig:bathymetry}
392 %\end{figure}
393
394
395 Figures (\ref{fig:sim_config_tclim_pcoord}-\ref{fig:sim_config_empmr_pcoord})
396 %(\ref{fig:sim_config_tclim}-\ref{fig:sim_config_empmr})
397 show the relaxation temperature ($\theta^{\ast}$) and salinity ($S^{\ast}$)
398 fields, the wind stress components ($\tau_x$ and $\tau_y$), the heat flux ($Q$)
399 and the net fresh water flux (${\cal E} - {\cal P} - {\cal R}$) used
400 in equations
401 (\ref{eq:eg-global-global_forcing_fu}-\ref{eq:eg-global-global_forcing_fs}).
402 The figures also indicate the lateral extent and coastline used in the
403 experiment. Figure ({\it --- missing figure --- }) %ref{fig:model_bathymetry})
404 shows the depth contours of the model domain.
405
406 \subsubsection{File {\it input/data}}
407 %\label{www:tutorials}
408
409 \input{s_examples/global_oce_latlon/inp_data}
410
411 \subsubsection{File {\it input/data.pkg}}
412 %\label{www:tutorials}
413
414 This file uses standard default values and does not contain
415 customisations for this experiment.
416
417 \subsubsection{File {\it input/eedata}}
418 %\label{www:tutorials}
419
420 This file uses standard default values and does not contain
421 customisations for this experiment.
422
423 \subsubsection{Files{\it input/trenberth\_taux.bin} and {\it
424 input/trenberth\_tauy.bin}}
425 %\label{www:tutorials}
426
427 The {\it input/trenberth\_taux.bin} and {\it
428 input/trenberth\_tauy.bin} files specify a three-dimensional
429 ($x,y,time$) map of wind stress, $(\tau_{x},\tau_{y})$, values
430 \citep{trenberth90}. The units used are $Nm^{-2}$.
431
432 \subsubsection{File {\it input/bathymetry.bin}}
433 %\label{www:tutorials}
434
435 The {\it input/bathymetry.bin} file specifies a two-dimensional
436 ($x,y$) map of depth values. For this experiment values range
437 between~$0$ and $-5200\,{\rm m}$, and have been derived from
438 ETOPO5. The file contains a raw binary stream of data that is
439 enumerated in the same way as standard MITgcm two-dimensional,
440 horizontal arrays.
441
442 \subsubsection{File {\it code/SIZE.h}}
443 %\label{www:tutorials}
444
445 \input{s_examples/global_oce_latlon/cod_SIZE.h}
446
447 %\subsubsection{File {\it code/CPP\_OPTIONS.h}}
448 %\label{www:tutorials}
449
450 %This file uses standard default values and does not contain
451 %customisations for this experiment.
452
453
454 %\subsubsection{File {\it code/CPP\_EEOPTIONS.h}}
455 %\label{www:tutorials}
456
457 %This file uses standard default values and does not contain
458 %customisations for this experiment.
459
460 \subsubsection{Other Files }
461 %\label{www:tutorials}
462
463 % Other files relevant to this experiment are
464 % \begin{itemize}
465 % \item {\it model/src/ini\_cori.F}. This file initializes the model
466 % coriolis variables {\bf fCorU}.
467 % \item {\it model/src/ini\_spherical\_polar\_grid.F}
468 % \item {\it model/src/ini\_parms.F},
469 % \item {\it input/windx.sin\_y},
470 % \end{itemize}
471 % contain the code customisations and parameter settings for this
472 % experiments. Below we describe the customisations
473 % to these files associated with this experiment.

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