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revision 1.3 by cnh, Thu Oct 25 18:36:55 2001 UTC revision 1.24 by jmc, Wed May 15 22:47:12 2013 UTC
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1  % $Header$  % $Header$
2  % $Name$  % $Name$
3    
4  \section{Example: 4$^\circ$ Global Climatological Ocean Simulation}  \section[Global Ocean MITgcm Example]{Global Ocean Simulation at $4^\circ$ Resolution}
5    %\label{www:tutorials}
6  \label{sec:eg-global}  \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"}  \bodytext{bgcolor="#FFFFFFFF"}
15    
16  %\begin{center}  \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  %{\Large \bf Using MITgcm to Simulate Global Climatological Ocean Circulation
21  %At Four Degree Resolution with Asynchronous Time Stepping}  %At Four Degree Resolution with Asynchronous Time Stepping}
22  %  %
# Line 16  Line 26 
26  %{\large May 2001}  %{\large May 2001}
27  %\end{center}  %\end{center}
28    
29  \subsection{Introduction}  This example experiment demonstrates using the MITgcm to simulate the
30    planetary ocean circulation. The simulation is configured with
31  This document describes the third example MITgcm experiment. The first  realistic geography and bathymetry on a $4^{\circ} \times 4^{\circ}$
32  two examples illustrated how to configure the code for hydrostatic idealized  spherical polar grid. The files for this experiment are in the
33  geophysical fluids simulations. This example illustrates the use of  verification directory under tutorial\_global\_oce\_latlon. Fifteen
34  the MITgcm for large scale ocean circulation simulation.  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}  \subsection{Overview}
43    %\label{www:tutorials}
44    
45  This example experiment demonstrates using the MITgcm to simulate  The model is forced with climatological wind stress data from
46  the planetary ocean circulation. The simulation is configured  \citet{trenberth90} and NCEP surface flux data from
47  with realistic geography and bathymetry on a  \citet{kalnay96}. Climatological data \citep{Levitus94} is
48  $4^{\circ} \times 4^{\circ}$ spherical polar grid.  used to initialize the model hydrography. \citeauthor{Levitus94} seasonal
49  Twenty levels are used in the vertical, ranging in thickness  climatology data is also used throughout the calculation to provide
50  from $50\,{\rm m}$ at the surface to $815\,{\rm m}$ at depth,  additional air-sea fluxes.  These fluxes are combined with the NCEP
51  giving a maximum model depth of $6\,{\rm km}$.  climatological estimates of surface heat flux, resulting in a mixed
52  At this resolution, the configuration  boundary condition of the style described in \citet{Haney}.
53  can be integrated forward for thousands of years on a single  Altogether, this yields the following forcing applied in the model
54  processor desktop computer.  surface layer.
 \\  
   
 The model is forced with climatological wind stress data and surface  
 flux data from DaSilva \cite{DaSilva94}. Climatological data  
 from Levitus \cite{Levitus94} is used to initialize the model hydrography.  
 Levitus seasonal climatology data is also used throughout the calculation  
 to provide additional air-sea fluxes.  
 These fluxes are combined with the DaSilva climatological estimates of  
 surface heat flux and fresh water, resulting in a mixed boundary  
 condition of the style described in Haney \cite{Haney}.  
 Altogether, this yields the following forcing applied  
 in the model surface layer.  
55    
56  \begin{eqnarray}  \begin{eqnarray}
57  \label{EQ:global_forcing}  \label{eq:eg-global-global_forcing}
58  \label{EQ:global_forcing_fu}  \label{eq:eg-global-global_forcing_fu}
59  {\cal F}_{u} & = & \frac{\tau_{x}}{\rho_{0} \Delta z_{s}}  {\cal F}_{u} & = & \frac{\tau_{x}}{\rho_{0} \Delta z_{s}}
60  \\  \\
61  \label{EQ:global_forcing_fv}  \label{eq:eg-global-global_forcing_fv}
62  {\cal F}_{v} & = & \frac{\tau_{y}}{\rho_{0} \Delta z_{s}}  {\cal F}_{v} & = & \frac{\tau_{y}}{\rho_{0} \Delta z_{s}}
63  \\  \\
64  \label{EQ:global_forcing_ft}  \label{eq:eg-global-global_forcing_ft}
65  {\cal F}_{\theta} & = & - \lambda_{\theta} ( \theta - \theta^{\ast} )  {\cal F}_{\theta} & = & - \lambda_{\theta} ( \theta - \theta^{\ast} )
66   - \frac{1}{C_{p} \rho_{0} \Delta z_{s}}{\cal Q}   - \frac{1}{C_{p} \rho_{0} \Delta z_{s}}{\cal Q}
67  \\  \\
68  \label{EQ:global_forcing_fs}  \label{eq:eg-global-global_forcing_fs}
69  {\cal F}_{s} & = & - \lambda_{s} ( S - S^{\ast} )  {\cal F}_{s} & = & - \lambda_{s} ( S - S^{\ast} )
70   + \frac{S_{0}}{\Delta z_{s}}({\cal E} - {\cal P} - {\cal R})   + \frac{S_{0}}{\Delta z_{s}}({\cal E} - {\cal P} - {\cal R})
71  \end{eqnarray}  \end{eqnarray}
72    
# Line 85  experiment are $\tau_{x}$, $\tau_{y}$, $ Line 90  experiment are $\tau_{x}$, $\tau_{y}$, $
90  $\cal{Q}$ and $\cal{E}-\cal{P}-\cal{R}$. The wind stress fields ($\tau_x$, $\tau_y$)  $\cal{Q}$ 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  have units of ${\rm N}~{\rm m}^{-2}$. The temperature forcing fields
92  ($\theta^{\ast}$ and $Q$) have units of $^{\circ}{\rm C}$ and ${\rm W}~{\rm m}^{-2}$  ($\theta^{\ast}$ and $Q$) have units of $^{\circ}{\rm C}$ and ${\rm W}~{\rm m}^{-2}$
93  respectively. The salinity forcing fields ($S^{\ast}$ and  respectively. The salinity forcing fields ($S^{\ast}$ and
94  $\cal{E}-\cal{P}-\cal{R}$) have units of ${\rm ppt}$ and ${\rm m}~{\rm s}^{-1}$  $\cal{E}-\cal{P}-\cal{R}$) have units of ${\rm ppt}$ and ${\rm m}~{\rm s}^{-1}$
95  respectively.  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}.
   
 Figures (\ref{FIG:sim_config_tclim}-\ref{FIG:sim_config_empmr}) show the  
 relaxation temperature ($\theta^{\ast}$) and salinity ($S^{\ast}$) fields,  
 the wind stress components ($\tau_x$ and $\tau_y$), the heat flux ($Q$)  
 and the net fresh water flux (${\cal E} - {\cal P} - {\cal R}$) used  
 in equations \ref{EQ:global_forcing_fu}-\ref{EQ:global_forcing_fs}. The figures  
 also indicate the lateral extent and coastline used in the experiment.  
 Figure ({\ref{FIG:model_bathymetry}) shows the depth contours of the model  
 domain.  
98    
99    
100  \subsection{Discrete Numerical Configuration}  \subsection{Discrete Numerical Configuration}
101    %\label{www:tutorials}
102    
103    
104   The model is configured in hydrostatic form.  The domain is discretised with  The model is configured in hydrostatic form.  The domain is
105  a uniform grid spacing in latitude and longitude on the sphere  discretised with a uniform grid spacing in latitude and longitude on
106   $\Delta \phi=\Delta \lambda=4^{\circ}$, so  the sphere $\Delta \phi=\Delta \lambda=4^{\circ}$, so that there are
107  that there are ninety grid cells in the zonal and forty in the  ninety grid cells in the zonal and forty in the meridional
108  meridional direction. The internal model coordinate variables  direction. The internal model coordinate variables $x$ and $y$ are
109  $x$ and $y$ are initialized according to  initialized according to
110  \begin{eqnarray}  \begin{eqnarray}
111  x=r\cos(\phi),~\Delta x & = &r\cos(\Delta \phi) \\  x=r\cos(\phi),~\Delta x & = &r\cos(\Delta \phi) \\
112  y=r\lambda,~\Delta x &= &r\Delta \lambda  y=r\lambda,~\Delta y &= &r\Delta \lambda
113  \end{eqnarray}  \end{eqnarray}
114    
115  Arctic polar regions are not  Arctic polar regions are not
116  included in this experiment. Meridionally the model extends from  included in this experiment. Meridionally the model extends from
117  $80^{\circ}{\rm S}$ to $80^{\circ}{\rm N}$.  $80^{\circ}{\rm S}$ to $80^{\circ}{\rm N}$.
118  Vertically the model is configured with twenty layers with the  Vertically the model is configured with fifteen layers with the
119  following thicknesses  following thicknesses:
120  $\Delta z_{1} = 50\,{\rm m},\,  $\Delta z_{1} = 50\,{\rm m},$\\
121   \Delta z_{2} = 50\,{\rm m},\,  $\Delta z_{2} = 70\,{\rm m},\,
122   \Delta z_{3} = 55\,{\rm m},\,   \Delta z_{3} = 100\,{\rm m},\,
123   \Delta z_{4} = 60\,{\rm m},\,   \Delta z_{4} = 140\,{\rm m},\,
124   \Delta z_{5} = 65\,{\rm m},\,   \Delta z_{5} = 190\,{\rm m},\,
125  $   \Delta z_{6} = 240\,{\rm m},\,
126  $   \Delta z_{7} = 290\,{\rm m},\,
127   \Delta z_{6}~=~70\,{\rm m},\,   \Delta z_{8} = 340\,{\rm m},$\\
128   \Delta z_{7}~=~80\,{\rm m},\,  $\Delta z_{9} = 390\,{\rm m},\,
129   \Delta z_{8}~=95\,{\rm m},\,   \Delta z_{10}= 440\,{\rm m},\,
130   \Delta z_{9}=120\,{\rm m},\,   \Delta z_{11}= 490\,{\rm m},\,
131   \Delta z_{10}=155\,{\rm m},\,   \Delta z_{12}= 540\,{\rm m},\,
132  $   \Delta z_{13}= 590\,{\rm m},\,
133  $   \Delta z_{14}= 640\,{\rm m},\,
134   \Delta z_{11}=200\,{\rm m},\,   \Delta z_{15}= 690\,{\rm m}$\\
135   \Delta z_{12}=260\,{\rm m},\,  (here the numeric subscript indicates the model level index number, ${\tt k}$) to
136   \Delta z_{13}=320\,{\rm m},\,  give a total depth, $H$, of $-5200{\rm m}$.
137   \Delta z_{14}=400\,{\rm m},\,  The implicit free surface form of the pressure equation described in
138   \Delta z_{15}=480\,{\rm m},\,  \citet{marshall:97a} is employed. A Laplacian operator, $\nabla^2$, provides viscous
 $  
 $  
  \Delta z_{16}=570\,{\rm m},\,  
  \Delta z_{17}=655\,{\rm m},\,  
  \Delta z_{18}=725\,{\rm m},\,  
  \Delta z_{19}=775\,{\rm m},\,  
  \Delta z_{20}=815\,{\rm m}  
 $ (here the numeric subscript indicates the model level index number, ${\tt k}$).  
 The implicit free surface form of the pressure equation described in Marshall et. al  
 \cite{Marshall97a} is employed. A Laplacian operator, $\nabla^2$, provides viscous  
139  dissipation. Thermal and haline diffusion is also represented by a Laplacian operator.  dissipation. Thermal and haline diffusion is also represented by a Laplacian operator.
140    
141  Wind-stress forcing is added to the momentum equations for both  Wind-stress forcing is added to the momentum equations in (\ref{eq:eg-global-model_equations})
142  the zonal flow, $u$ and the meridional flow $v$, according to equations  for both the zonal flow, $u$ and the meridional flow $v$, according to equations
143  (\ref{EQ:global_forcing_fu}) and (\ref{EQ:global_forcing_fv}).  (\ref{eq:eg-global-global_forcing_fu}) and (\ref{eq:eg-global-global_forcing_fv}).
144  Thermodynamic forcing inputs are added to the equations for  Thermodynamic forcing inputs are added to the equations
145  potential temperature, $\theta$, and salinity, $S$, according to equations  in (\ref{eq:eg-global-model_equations}) for
146  (\ref{EQ:global_forcing_ft}) and (\ref{EQ:global_forcing_fs}).  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:  This produces a set of equations solved in this configuration as follows:
149    
150  \begin{eqnarray}  \begin{eqnarray}
151  \label{EQ:model_equations}  \label{eq:eg-global-model_equations}
152  \frac{Du}{Dt} - fv +  \frac{Du}{Dt} - fv +
153    \frac{1}{\rho}\frac{\partial p^{'}}{\partial x} -    \frac{1}{\rho}\frac{\partial p^{'}}{\partial x} -
154    \nabla_{h}\cdot A_{h}\nabla_{h}u -    \nabla_{h}\cdot A_{h}\nabla_{h}u -
155    \frac{\partial}{\partial z}A_{z}\frac{\partial u}{\partial z}    \frac{\partial}{\partial z}A_{z}\frac{\partial u}{\partial z}
156   & = &   & = &
157  \begin{cases}  \begin{cases}
158  {\cal F}_u & \text{(surface)} \\  {\cal F}_u & \text{(surface)} \\
159  0 & \text{(interior)}  0 & \text{(interior)}
160  \end{cases}  \end{cases}
161  \\  \\
162  \frac{Dv}{Dt} + fu +  \frac{Dv}{Dt} + fu +
163    \frac{1}{\rho}\frac{\partial p^{'}}{\partial y} -    \frac{1}{\rho}\frac{\partial p^{'}}{\partial y} -
164    \nabla_{h}\cdot A_{h}\nabla_{h}v -    \nabla_{h}\cdot A_{h}\nabla_{h}v -
165    \frac{\partial}{\partial z}A_{z}\frac{\partial v}{\partial z}    \frac{\partial}{\partial z}A_{z}\frac{\partial v}{\partial z}
166  & = &  & = &
167  \begin{cases}  \begin{cases}
168  {\cal F}_v & \text{(surface)} \\  {\cal F}_v & \text{(surface)} \\
# Line 187  This produces a set of equations solved Line 175  This produces a set of equations solved
175  \\  \\
176  \frac{D\theta}{Dt} -  \frac{D\theta}{Dt} -
177   \nabla_{h}\cdot K_{h}\nabla_{h}\theta   \nabla_{h}\cdot K_{h}\nabla_{h}\theta
178   - \frac{\partial}{\partial z}\Gamma(K_{z})\frac{\partial\theta}{\partial z}   - \frac{\partial}{\partial z}\Gamma(K_{z})\frac{\partial\theta}{\partial z}
179  & = &  & = &
180  \begin{cases}  \begin{cases}
181  {\cal F}_\theta & \text{(surface)} \\  {\cal F}_\theta & \text{(surface)} \\
# Line 196  This produces a set of equations solved Line 184  This produces a set of equations solved
184  \\  \\
185  \frac{D s}{Dt} -  \frac{D s}{Dt} -
186   \nabla_{h}\cdot K_{h}\nabla_{h}s   \nabla_{h}\cdot K_{h}\nabla_{h}s
187   - \frac{\partial}{\partial z}\Gamma(K_{z})\frac{\partial s}{\partial z}   - \frac{\partial}{\partial z}\Gamma(K_{z})\frac{\partial s}{\partial z}
188  & = &  & = &
189  \begin{cases}  \begin{cases}
190  {\cal F}_s & \text{(surface)} \\  {\cal F}_s & \text{(surface)} \\
# Line 206  This produces a set of equations solved Line 194  This produces a set of equations solved
194  g\rho_{0} \eta + \int^{0}_{-z}\rho^{'} dz & = & p^{'}  g\rho_{0} \eta + \int^{0}_{-z}\rho^{'} dz & = & p^{'}
195  \end{eqnarray}  \end{eqnarray}
196    
197  \noindent where $u=\frac{Dx}{Dt}=r \cos(\phi)\frac{D \lambda}{Dt}$ and  \noindent where $u=\frac{Dx}{Dt}=r \cos(\phi)\frac{D \lambda}{Dt}$ and
198  $v=\frac{Dy}{Dt}=r \frac{D \phi}{Dt}$  $v=\frac{Dy}{Dt}=r \frac{D \phi}{Dt}$
199  are the zonal and meridional components of the  are the zonal and meridional components of the
200  flow vector, $\vec{u}$, on the sphere. As described in  flow vector, $\vec{u}$, on the sphere. As described in
201  MITgcm Numerical Solution Procedure \cite{MITgcm_Numerical_Scheme}, the time  MITgcm Numerical Solution Procedure \ref{chap:discretization}, the time
202  evolution of potential temperature, $\theta$, equation is solved prognostically.  evolution of potential temperature, $\theta$, equation is solved prognostically.
203  The total pressure, $p$, is diagnosed by summing pressure due to surface  The total pressure, $p$, is diagnosed by summing pressure due to surface
204  elevation $\eta$ and the hydrostatic pressure.  elevation $\eta$ and the hydrostatic pressure.
205  \\  \\
206    
207  \subsubsection{Numerical Stability Criteria}  \subsubsection{Numerical Stability Criteria}
208    %\label{www:tutorials}
209    
210  The Laplacian dissipation coefficient, $A_{h}$, is set to $5 \times 10^5 m s^{-1}$.  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 \cite{Adcroft_thesis},  This value is chosen to yield a Munk layer width \citep{adcroft:95},
212  \begin{eqnarray}  \begin{eqnarray}
213  \label{EQ:munk_layer}  \label{eq:eg-global-munk_layer}
214  M_{w} = \pi ( \frac { A_{h} }{ \beta } )^{\frac{1}{3}}  && M_{w} = \pi ( \frac { A_{h} }{ \beta } )^{\frac{1}{3}}
215  \end{eqnarray}  \end{eqnarray}
216    
217  \noindent  of $\approx 600$km. This is greater than the model  \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  resolution in low-latitudes, $\Delta x \approx 400{\rm km}$, ensuring that the frictional
219  boundary layer is adequately resolved.  boundary layer is adequately resolved.
220  \\  \\
221    
222  \noindent The model is stepped forward with a  \noindent The model is stepped forward with a time step $\Delta
223  time step $\delta t_{\theta}=30~{\rm hours}$ for thermodynamic variables and  t_{\theta}=24~{\rm hours}$ for thermodynamic variables and $\Delta
224  $\delta t_{v}=40~{\rm minutes}$ for momentum terms. With this time step, the stability  t_{v}=30~{\rm minutes}$ for momentum terms. With this time step,
225  parameter to the horizontal Laplacian friction \cite{Adcroft_thesis}  the stability parameter to the horizontal Laplacian friction
226    \citep{adcroft:95}
227  \begin{eqnarray}  \begin{eqnarray}
228  \label{EQ:laplacian_stability}  \label{eq:eg-global-laplacian_stability}
229  S_{l} = 4 \frac{A_{h} \delta t_{v}}{{\Delta x}^2}  && S_{l} = 4 \frac{A_{h} \Delta t_{v}}{{\Delta x}^2}
230  \end{eqnarray}  \end{eqnarray}
231    
232  \noindent evaluates to 0.16 at a latitude of $\phi=80^{\circ}$, which is below the  \noindent evaluates to 0.6 at a latitude of $\phi=80^{\circ}$, which
233  0.3 upper limit for stability. The zonal grid spacing $\Delta x$ is smallest at  is above the 0.3 upper limit for stability, but the zonal grid spacing
234  $\phi=80^{\circ}$ where $\Delta x=r\cos(\phi)\Delta \phi\approx 77{\rm km}$.  $\Delta x$ 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  \noindent The vertical dissipation coefficient, $A_{z}$, is set to  
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  $1\times10^{-3} {\rm m}^2{\rm s}^{-1}$. The associated stability limit
241  \begin{eqnarray}  \begin{eqnarray}
242  \label{EQ:laplacian_stability_z}  \label{eq:eg-global-laplacian_stability_z}
243  S_{l} = 4 \frac{A_{z} \delta t_{v}}{{\Delta z}^2}  && S_{l} = 4 \frac{A_{z} \Delta t_{v}}{{\Delta z}^2}
244  \end{eqnarray}  \end{eqnarray}
245    
246  \noindent evaluates to $0.015$ for the smallest model  \noindent evaluates to $0.0029$ for the smallest model
247  level spacing ($\Delta z_{1}=50{\rm m}$) which is again well below  level spacing ($\Delta z_{1}=50{\rm m}$) which is well below
248  the upper stability limit.  the upper stability limit.
249  \\  \\
250    
251  The values of the horizontal ($K_{h}$) and vertical ($K_{z}$) diffusion coefficients  % The values of the horizontal ($K_{h}$) and vertical ($K_{z}$) diffusion coefficients
252  for both temperature and salinity are set to $1 \times 10^{3}~{\rm m}^{2}{\rm s}^{-1}$  % 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  % 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 $\Delta x \approx 77 {\rm km}$.  % related to $K_{h}$ will be at $\phi=80^{\circ}$ where $\Delta x \approx 77 {\rm km}$.
255  Here the stability parameter  % Here the stability parameter
256  \begin{eqnarray}  % \begin{eqnarray}
257  \label{EQ:laplacian_stability_xtheta}  % \label{eq:eg-global-laplacian_stability_xtheta}
258  S_{l} = \frac{4 K_{h} \delta t_{\theta}}{{\Delta x}^2}  % S_{l} = \frac{4 K_{h} \Delta t_{\theta}}{{\Delta x}^2}
259  \end{eqnarray}  % \end{eqnarray}
260  evaluates to $0.07$, well below the stability limit of $S_{l} \approx 0.5$. The  % evaluates to $0.07$, well below the stability limit of $S_{l} \approx 0.5$. The
261  stability parameter related to $K_{z}$  % stability parameter related to $K_{z}$
262  \begin{eqnarray}  % \begin{eqnarray}
263  \label{EQ:laplacian_stability_ztheta}  % \label{eq:eg-global-laplacian_stability_ztheta}
264  S_{l} = \frac{4 K_{z} \delta t_{\theta}}{{\Delta z}^2}  % S_{l} = \frac{4 K_{z} \Delta t_{\theta}}{{\Delta z}^2}
265  \end{eqnarray}  % \end{eqnarray}
266  evaluates to $0.005$ for $\min(\Delta z)=50{\rm m}$, well below the stability limit  % evaluates to $0.005$ for $\min(\Delta z)=50{\rm m}$, well below the stability limit
267  of $S_{l} \approx 0.5$.  % of $S_{l} \approx 0.5$.
268  \\  % \\
269    
270  \noindent The numerical stability for inertial oscillations  \noindent The numerical stability for inertial oscillations
271  \cite{Adcroft_thesis}  \citep{adcroft:95}
272    
273  \begin{eqnarray}  \begin{eqnarray}
274  \label{EQ:inertial_stability}  \label{eq:eg-global-inertial_stability}
275  S_{i} = f^{2} {\delta t_v}^2  && S_{i} = f^{2} {\Delta t_v}^2
276  \end{eqnarray}  \end{eqnarray}
277    
278  \noindent evaluates to $0.24$ for $f=2\omega\sin(80^{\circ})=1.43\times10^{-4}~{\rm s}^{-1}$, which is close to  \noindent evaluates to $0.07$ for
279  the $S_{i} < 1$ upper limit for stability.  $f=2\omega\sin(80^{\circ})=1.43\times10^{-4}~{\rm s}^{-1}$, which is
280    below the $S_{i} < 1$ upper limit for stability.
281  \\  \\
282    
283  \noindent The advective CFL \cite{Adcroft_thesis} for a extreme maximum  \noindent The advective CFL \citep{adcroft:95} for a extreme maximum
284  horizontal flow  horizontal flow
285  speed of $ | \vec{u} | = 2 ms^{-1}$  speed of $ | \vec{u} | = 2 ms^{-1}$
286    
287  \begin{eqnarray}  \begin{eqnarray}
288  \label{EQ:cfl_stability}  \label{eq:eg-global-cfl_stability}
289  S_{a} = \frac{| \vec{u} | \delta t_{v}}{ \Delta x}  && S_{a} = \frac{| \vec{u} | \Delta t_{v}}{ \Delta x}
290  \end{eqnarray}  \end{eqnarray}
291    
292  \noindent evaluates to $6 \times 10^{-2}$. This is well below the stability  \noindent evaluates to $5 \times 10^{-2}$. This is well below the stability
293  limit of 0.5.  limit of 0.5.
294  \\  \\
295    
296  \noindent The stability parameter for internal gravity waves propagating  \noindent The stability parameter for internal gravity waves propagating
297  with a maximum speed of $c_{g}=10~{\rm ms}^{-1}$   with a maximum speed of $c_{g}=10~{\rm ms}^{-1}$
298  \cite{Adcroft_thesis}  \citep{adcroft:95}
299    
300  \begin{eqnarray}  \begin{eqnarray}
301  \label{EQ:cfl_stability}  \label{eq:eg-global-gfl_stability}
302  S_{c} = \frac{c_{g} \delta t_{v}}{ \Delta x}  && S_{c} = \frac{c_{g} \Delta t_{v}}{ \Delta x}
303  \end{eqnarray}  \end{eqnarray}
304    
305  \noindent evaluates to $3 \times 10^{-1}$. This is close to the linear  \noindent evaluates to $2.3 \times 10^{-1}$. This is close to the linear
306  stability limit of 0.5.  stability limit of 0.5.
307      
308  \subsection{Experiment Configuration}  \subsection{Experiment Configuration}
309  \label{SEC:clim_ocn_examp_exp_config}  %\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    
 The model configuration for this experiment resides under the  
 directory {\it verification/exp2/}.  The experiment files  
315  \begin{itemize}  \begin{itemize}
316  \item {\it input/data}  \item {\it input/data}
317  \item {\it input/data.pkg}  \item {\it input/data.pkg}
318  \item {\it input/eedata},  \item {\it input/eedata},
319  \item {\it input/windx.bin},  \item {\it input/trenberth\_taux.bin},
320  \item {\it input/windy.bin},  \item {\it input/trenberth\_tauy.bin},
321  \item {\it input/salt.bin},  \item {\it input/lev\_s.bin},
322  \item {\it input/theta.bin},  \item {\it input/lev\_t.bin},
323  \item {\it input/SSS.bin},  \item {\it input/lev\_sss.bin},
324  \item {\it input/SST.bin},  \item {\it input/lev\_sst.bin},
325  \item {\it input/topog.bin},  \item {\it input/bathymetry.bin},
326  \item {\it code/CPP\_EEOPTIONS.h}  %\item {\it code/CPP\_EEOPTIONS.h}
327  \item {\it code/CPP\_OPTIONS.h},  %\item {\it code/CPP\_OPTIONS.h},
328  \item {\it code/SIZE.h}.  \item {\it code/SIZE.h}.
329  \end{itemize}  \end{itemize}
330  contain the code customizations and parameter settings for these  contain the code customizations and parameter settings for these
331  experiments. Below we describe the customizations  experiments. Below we describe the customizations
332  to these files associated with this experiment.  to these files associated with this experiment.
333    
334  \subsubsection{File {\it input/data}}  \subsubsection{Driving Datasets}
335    %\label{www:tutorials}
 This file, reproduced completely below, specifies the main parameters  
 for the experiment. The parameters that are significant for this configuration  
 are  
336    
337  \begin{itemize}  %% New figures are included before
338    %% Relaxation temperature
339  \item Lines 7-10 and 11-14  %\begin{figure}
340  \begin{verbatim} tRef= 16.0 , 15.2 , 14.5 , 13.9 , 13.3 ,  \end{verbatim}  %\centering
341  $\cdots$ \\  %\includegraphics[]{relax_temperature.eps}
342  set reference values for potential  %\caption{Relaxation temperature for January}
343  temperature and salinity at each model level in units of $^{\circ}$C and  %\label{fig:relax_temperature}
344  ${\rm ppt}$. The entries are ordered from surface to depth.  %\end{figure}
345  Density is calculated from anomalies at each level evaluated  
346  with respect to the reference values set here.\\  %% Relaxation salinity
347  \fbox{  %\begin{figure}
348  \begin{minipage}{5.0in}  %\centering
349  {\it S/R INI\_THETA}({\it ini\_theta.F})  %\includegraphics[]{relax_salinity.eps}
350  \end{minipage}  %\caption{Relaxation salinity for January}
351  }  %\label{fig:relax_salinity}
352    %\end{figure}
353    
354  \item Line 15,  %% tau_x
355  \begin{verbatim} viscAz=1.E-3, \end{verbatim}  %\begin{figure}
356  this line sets the vertical Laplacian dissipation coefficient to  %\centering
357  $1 \times 10^{-3} {\rm m^{2}s^{-1}}$. Boundary conditions  %\includegraphics[]{tau_x.eps}
358  for this operator are specified later. This variable is copied into  %\caption{zonal wind stress for January}
359  model general vertical coordinate variable {\bf viscAr}.  %\label{fig:tau_x}
360    %\end{figure}
361  \fbox{  
362  \begin{minipage}{5.0in}  %% tau_y
363  {\it S/R CALC\_DIFFUSIVITY}({\it calc\_diffusivity.F})  %\begin{figure}
364  \end{minipage}  %\centering
365  }  %\includegraphics[]{tau_y.eps}
366    %\caption{meridional wind stress for January}
367  \item Line 16,  %\label{fig:tau_y}
368  \begin{verbatim}  %\end{figure}
369  viscAh=5.E5,  
370  \end{verbatim}  %% Qnet
371  this line sets the horizontal Laplacian frictional dissipation coefficient to  %\begin{figure}
372  $5 \times 10^{5} {\rm m^{2}s^{-1}}$. Boundary conditions  %\centering
373  for this operator are specified later.  %\includegraphics[]{qnet.eps}
374    %\caption{Heat flux for January}
375  \item Lines 17,  %\label{fig:qnet}
376  \begin{verbatim}  %\end{figure}
377  no_slip_sides=.FALSE.  
378  \end{verbatim}  %% EmPmR
379  this line selects a free-slip lateral boundary condition for  %\begin{figure}
380  the horizontal Laplacian friction operator  %\centering
381  e.g. $\frac{\partial u}{\partial y}$=0 along boundaries in $y$ and  %\includegraphics[]{empmr.eps}
382  $\frac{\partial v}{\partial x}$=0 along boundaries in $x$.  %\caption{Fresh water flux for January}
383    %\label{fig:empmr}
384  \item Lines 9,  %\end{figure}
385  \begin{verbatim}  
386  no_slip_bottom=.TRUE.  %% Bathymetry
387  \end{verbatim}  %\begin{figure}
388  this line selects a no-slip boundary condition for bottom  %\centering
389  boundary condition in the vertical Laplacian friction operator  %\includegraphics[]{bathymetry.eps}
390  e.g. $u=v=0$ at $z=-H$, where $H$ is the local depth of the domain.  %\caption{Bathymetry}
391    %\label{fig:bathymetry}
392  \item Line 19,  %\end{figure}
393  \begin{verbatim}  
394  diffKhT=1.E3,  
395  \end{verbatim}  Figures (\ref{fig:sim_config_tclim_pcoord}-\ref{fig:sim_config_empmr_pcoord})
396  this line sets the horizontal diffusion coefficient for temperature  %(\ref{fig:sim_config_tclim}-\ref{fig:sim_config_empmr})
397  to $1000\,{\rm m^{2}s^{-1}}$. The boundary condition on this  show the relaxation temperature ($\theta^{\ast}$) and salinity ($S^{\ast}$)
398  operator is $\frac{\partial}{\partial x}=\frac{\partial}{\partial y}=0$ on  fields, the wind stress components ($\tau_x$ and $\tau_y$), the heat flux ($Q$)
399  all boundaries.  and the net fresh water flux (${\cal E} - {\cal P} - {\cal R}$) used
400    in equations
401  \item Line 20,  (\ref{eq:eg-global-global_forcing_fu}-\ref{eq:eg-global-global_forcing_fs}).
402  \begin{verbatim}  The figures also indicate the lateral extent and coastline used in the
403  diffKzT=3.E-5,  experiment. Figure ({\it --- missing figure --- }) %ref{fig:model_bathymetry})
404  \end{verbatim}  shows the depth contours of the model domain.
 this line sets the vertical diffusion coefficient for temperature  
 to $3 \times 10^{-5}\,{\rm m^{2}s^{-1}}$. The boundary  
 condition on this operator is $\frac{\partial}{\partial z}=0$ at both  
 the upper and lower boundaries.  
   
 \item Line 21,  
 \begin{verbatim}  
 diffKhS=1.E3,  
 \end{verbatim}  
 this line sets the horizontal diffusion coefficient for salinity  
 to $1000\,{\rm m^{2}s^{-1}}$. The boundary condition on this  
 operator is $\frac{\partial}{\partial x}=\frac{\partial}{\partial y}=0$ on  
 all boundaries.  
   
 \item Line 22,  
 \begin{verbatim}  
 diffKzS=3.E-5,  
 \end{verbatim}  
 this line sets the vertical diffusion coefficient for salinity  
 to $3 \times 10^{-5}\,{\rm m^{2}s^{-1}}$. The boundary  
 condition on this operator is $\frac{\partial}{\partial z}=0$ at both  
 the upper and lower boundaries.  
   
 \item Lines 23-26  
 \begin{verbatim}  
 beta=1.E-11,  
 \end{verbatim}  
 \vspace{-5mm}$\cdots$\\  
 These settings do not apply for this experiment.  
   
 \item Line 27,  
 \begin{verbatim}  
 gravity=9.81,  
 \end{verbatim}  
 Sets the gravitational acceleration coefficient to $9.81{\rm m}{\rm s}^{-1}$.\\  
 \fbox{  
 \begin{minipage}{5.0in}  
 {\it S/R CALC\_PHI\_HYD}~({\it calc\_phi\_hyd.F})\\  
 {\it S/R INI\_CG2D}~({\it ini\_cg2d.F})\\  
 {\it S/R INI\_CG3D}~({\it ini\_cg3d.F})\\  
 {\it S/R INI\_PARMS}~({\it ini\_parms.F})\\  
 {\it S/R SOLVE\_FOR\_PRESSURE}~({\it solve\_for\_pressure.F})  
 \end{minipage}  
 }  
   
   
 \item Line 28-29,  
 \begin{verbatim}  
 rigidLid=.FALSE.,  
 implicitFreeSurface=.TRUE.,  
 \end{verbatim}  
 Selects the barotropic pressure equation to be the implicit free surface  
 formulation.  
   
 \item Line 30,  
 \begin{verbatim}  
 eosType='POLY3',  
 \end{verbatim}  
 Selects the third order polynomial form of the equation of state.\\  
 \fbox{  
 \begin{minipage}{5.0in}  
 {\it S/R FIND\_RHO}~({\it find\_rho.F})\\  
 {\it S/R FIND\_ALPHA}~({\it find\_alpha.F})  
 \end{minipage}  
 }  
   
 \item Line 31,  
 \begin{verbatim}  
 readBinaryPrec=32,  
 \end{verbatim}  
 Sets format for reading binary input datasets holding model fields to  
 use 32-bit representation for floating-point numbers.\\  
 \fbox{  
 \begin{minipage}{5.0in}  
 {\it S/R READ\_WRITE\_FLD}~({\it read\_write\_fld.F})\\  
 {\it S/R READ\_WRITE\_REC}~({\it read\_write\_rec.F})  
 \end{minipage}  
 }  
   
 \item Line 36,  
 \begin{verbatim}  
 cg2dMaxIters=1000,  
 \end{verbatim}  
 Sets maximum number of iterations the two-dimensional, conjugate  
 gradient solver will use, {\bf irrespective of convergence  
 criteria being met}.\\  
 \fbox{  
 \begin{minipage}{5.0in}  
 {\it S/R CG2D}~({\it cg2d.F})  
 \end{minipage}  
 }  
   
 \item Line 37,  
 \begin{verbatim}  
 cg2dTargetResidual=1.E-13,  
 \end{verbatim}  
 Sets the tolerance which the two-dimensional, conjugate  
 gradient solver will use to test for convergence in equation  
 \ref{EQ:congrad_2d_resid} to $1 \times 10^{-13}$.  
 Solver will iterate until  
 tolerance falls below this value or until the maximum number of  
 solver iterations is reached.\\  
 \fbox{  
 \begin{minipage}{5.0in}  
 {\it S/R CG2D}~({\it cg2d.F})  
 \end{minipage}  
 }  
   
 \item Line 42,  
 \begin{verbatim}  
 startTime=0,  
 \end{verbatim}  
 Sets the starting time for the model internal time counter.  
 When set to non-zero this option implicitly requests a  
 checkpoint file be read for initial state.  
 By default the checkpoint file is named according to  
 the integer number of time steps in the {\bf startTime} value.  
 The internal time counter works in seconds.  
   
 \item Line 43,  
 \begin{verbatim}  
 endTime=2808000.,  
 \end{verbatim}  
 Sets the time (in seconds) at which this simulation will terminate.  
 At the end of a simulation a checkpoint file is automatically  
 written so that a numerical experiment can consist of multiple  
 stages.  
   
 \item Line 44,  
 \begin{verbatim}  
 #endTime=62208000000,  
 \end{verbatim}  
 A commented out setting for endTime for a 2000 year simulation.  
   
 \item Line 45,  
 \begin{verbatim}  
 deltaTmom=2400.0,  
 \end{verbatim}  
 Sets the timestep $\delta t_{v}$ used in the momentum equations to  
 $20~{\rm mins}$.  
 See section \ref{SEC:mom_time_stepping}.  
   
 \fbox{  
 \begin{minipage}{5.0in}  
 {\it S/R TIMESTEP}({\it timestep.F})  
 \end{minipage}  
 }  
   
 \item Line 46,  
 \begin{verbatim}  
 tauCD=321428.,  
 \end{verbatim}  
 Sets the D-grid to C-grid coupling time scale $\tau_{CD}$ used in the momentum equations.  
 See section \ref{SEC:cd_scheme}.  
   
 \fbox{  
 \begin{minipage}{5.0in}  
 {\it S/R INI\_PARMS}({\it ini\_parms.F})\\  
 {\it S/R CALC\_MOM\_RHS}({\it calc\_mom\_rhs.F})  
 \end{minipage}  
 }  
   
 \item Line 47,  
 \begin{verbatim}  
 deltaTtracer=108000.,  
 \end{verbatim}  
 Sets the default timestep, $\delta t_{\theta}$, for tracer equations to  
 $30~{\rm hours}$.  
 See section \ref{SEC:tracer_time_stepping}.  
   
 \fbox{  
 \begin{minipage}{5.0in}  
 {\it S/R TIMESTEP\_TRACER}({\it timestep\_tracer.F})  
 \end{minipage}  
 }  
   
 \item Line 47,  
 \begin{verbatim}  
 bathyFile='topog.box'  
 \end{verbatim}  
 This line specifies the name of the file from which the domain  
 bathymetry is read. This file is a two-dimensional ($x,y$) map of  
 depths. This file is assumed to contain 64-bit binary numbers  
 giving the depth of the model at each grid cell, ordered with the x  
 coordinate varying fastest. The points are ordered from low coordinate  
 to high coordinate for both axes. The units and orientation of the  
 depths in this file are the same as used in the MITgcm code. In this  
 experiment, a depth of $0m$ indicates a solid wall and a depth  
 of $-2000m$ indicates open ocean. The matlab program  
 {\it input/gendata.m} shows an example of how to generate a  
 bathymetry file.  
   
   
 \item Line 50,  
 \begin{verbatim}  
 zonalWindFile='windx.sin_y'  
 \end{verbatim}  
 This line specifies the name of the file from which the x-direction  
 surface wind stress is read. This file is also a two-dimensional  
 ($x,y$) map and is enumerated and formatted in the same manner as the  
 bathymetry file. The matlab program {\it input/gendata.m} includes example  
 code to generate a valid  
 {\bf zonalWindFile}  
 file.    
405    
406  \end{itemize}  \subsubsection{File {\it input/data}}
407    %\label{www:tutorials}
408    
409  \noindent other lines in the file {\it input/data} are standard values  \input{s_examples/global_oce_latlon/inp_data}
 that are described in the MITgcm Getting Started and MITgcm Parameters  
 notes.  
   
 \begin{small}  
 \input{part3/case_studies/climatalogical_ogcm/input/data}  
 \end{small}  
410    
411  \subsubsection{File {\it input/data.pkg}}  \subsubsection{File {\it input/data.pkg}}
412    %\label{www:tutorials}
413    
414  This file uses standard default values and does not contain  This file uses standard default values and does not contain
415  customisations for this experiment.  customisations for this experiment.
416    
417  \subsubsection{File {\it input/eedata}}  \subsubsection{File {\it input/eedata}}
418    %\label{www:tutorials}
419    
420  This file uses standard default values and does not contain  This file uses standard default values and does not contain
421  customisations for this experiment.  customisations for this experiment.
422    
423  \subsubsection{File {\it input/windx.sin\_y}}  \subsubsection{Files{\it input/trenberth\_taux.bin} and {\it
424      input/trenberth\_tauy.bin}}
425    %\label{www:tutorials}
426    
427  The {\it input/windx.sin\_y} file specifies a two-dimensional ($x,y$)  The {\it input/trenberth\_taux.bin} and {\it
428  map of wind stress ,$\tau_{x}$, values. The units used are $Nm^{-2}$.    input/trenberth\_tauy.bin} files specify a three-dimensional
429  Although $\tau_{x}$ is only a function of $y$n in this experiment  ($x,y,time$) map of wind stress, $(\tau_{x},\tau_{y})$, values
430  this file must still define a complete two-dimensional map in order  \citep{trenberth90}. The units used are $Nm^{-2}$.
 to be compatible with the standard code for loading forcing fields  
 in MITgcm. The included matlab program {\it input/gendata.m} gives a complete  
 code for creating the {\it input/windx.sin\_y} file.  
431    
432  \subsubsection{File {\it input/topog.box}}  \subsubsection{File {\it input/bathymetry.bin}}
433    %\label{www:tutorials}
434    
435    
436  The {\it input/topog.box} file specifies a two-dimensional ($x,y$)  The {\it input/topog.box} file specifies a two-dimensional ($x,y$)
437  map of depth values. For this experiment values are either  map of depth values. For this experiment values are either
438  $0m$ or $-2000\,{\rm m}$, corresponding respectively to a wall or to deep  $0m$ or $-5200\,{\rm m}$, corresponding respectively to a wall or to deep
439  ocean. The file contains a raw binary stream of data that is enumerated  ocean. The file contains a raw binary stream of data that is enumerated
440  in the same way as standard MITgcm two-dimensional, horizontal arrays.  in the same way as standard MITgcm two-dimensional, horizontal arrays.
441  The included matlab program {\it input/gendata.m} gives a complete  The included matlab program {\it input/gendata.m} gives a complete
442  code for creating the {\it input/topog.box} file.  code for creating the {\it input/topog.box} file.
443    
444  \subsubsection{File {\it code/SIZE.h}}  \subsubsection{File {\it code/SIZE.h}}
445    %\label{www:tutorials}
446    
447  Two lines are customized in this file for the current experiment  \input{s_examples/global_oce_latlon/cod_SIZE.h}
448    
449  \begin{itemize}  %\subsubsection{File {\it code/CPP\_OPTIONS.h}}
450    %\label{www:tutorials}
451    
452  \item Line 39,  %This file uses standard default values and does not contain
453  \begin{verbatim} sNx=60, \end{verbatim} this line sets  %customisations for this experiment.
 the lateral domain extent in grid points for the  
 axis aligned with the x-coordinate.  
   
 \item Line 40,  
 \begin{verbatim} sNy=60, \end{verbatim} this line sets  
 the lateral domain extent in grid points for the  
 axis aligned with the y-coordinate.  
   
 \item Line 49,  
 \begin{verbatim} Nr=4,   \end{verbatim} this line sets  
 the vertical domain extent in grid points.  
454    
 \end{itemize}  
   
 \begin{small}  
 \input{part3/case_studies/climatalogical_ogcm/code/SIZE.h}  
 \end{small}  
455    
456  \subsubsection{File {\it code/CPP\_OPTIONS.h}}  %\subsubsection{File {\it code/CPP\_EEOPTIONS.h}}
457    %\label{www:tutorials}
458    
459  This file uses standard default values and does not contain  %This file uses standard default values and does not contain
460  customisations for this experiment.  %customisations for this experiment.
   
   
 \subsubsection{File {\it code/CPP\_EEOPTIONS.h}}  
   
 This file uses standard default values and does not contain  
 customisations for this experiment.  
461    
462  \subsubsection{Other Files }  \subsubsection{Other Files }
463    %\label{www:tutorials}
464    
465  Other files relevant to this experiment are  % Other files relevant to this experiment are
466  \begin{itemize}  % \begin{itemize}
467  \item {\it model/src/ini\_cori.F}. This file initializes the model  % \item {\it model/src/ini\_cori.F}. This file initializes the model
468  coriolis variables {\bf fCorU}.  % coriolis variables {\bf fCorU}.
469  \item {\it model/src/ini\_spherical\_polar\_grid.F}  % \item {\it model/src/ini\_spherical\_polar\_grid.F}
470  \item {\it model/src/ini\_parms.F},  % \item {\it model/src/ini\_parms.F},
471  \item {\it input/windx.sin\_y},  % \item {\it input/windx.sin\_y},
472  \end{itemize}  % \end{itemize}
473  contain the code customisations and parameter settings for this  % contain the code customisations and parameter settings for this
474  experiments. Below we describe the customisations  % experiments. Below we describe the customisations
475  to these files associated with this experiment.  % to these files associated with this experiment.

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