20 |
to simulate a baroclinic ocean gyre in spherical |
to simulate a baroclinic ocean gyre in spherical |
21 |
polar coordinates. The barotropic |
polar coordinates. The barotropic |
22 |
example experiment in section \ref{sec:eg-baro} |
example experiment in section \ref{sec:eg-baro} |
23 |
ilustrated how to configure the code for a single layer |
illustrated how to configure the code for a single layer |
24 |
simulation in a cartesian grid. In this example a similar physical problem |
simulation in a Cartesian grid. In this example a similar physical problem |
25 |
is simulated, but the code is now configured |
is simulated, but the code is now configured |
26 |
for four layers and in a spherical polar coordinate system. |
for four layers and in a spherical polar coordinate system. |
27 |
|
|
29 |
|
|
30 |
This example experiment demonstrates using the MITgcm to simulate |
This example experiment demonstrates using the MITgcm to simulate |
31 |
a baroclinic, wind-forced, ocean gyre circulation. The experiment |
a baroclinic, wind-forced, ocean gyre circulation. The experiment |
32 |
is a numerical rendition of the gyre circulation problem simliar |
is a numerical rendition of the gyre circulation problem similar |
33 |
to the problems described analytically by Stommel in 1966 |
to the problems described analytically by Stommel in 1966 |
34 |
\cite{Stommel66} and numerically in Holland et. al \cite{Holland75}. |
\cite{Stommel66} and numerically in Holland et. al \cite{Holland75}. |
35 |
\\ |
\\ |
62 |
\\ |
\\ |
63 |
|
|
64 |
Figure \ref{FIG:simulation_config} |
Figure \ref{FIG:simulation_config} |
65 |
summarises the configuration simulated. |
summarizes the configuration simulated. |
66 |
In contrast to the example in section \ref{sec:eg-baro}, the |
In contrast to the example in section \ref{sec:eg-baro}, the |
67 |
current experiment simulates a spherical polar domain. As indicated |
current experiment simulates a spherical polar domain. As indicated |
68 |
by the axes in the lower left of the figure the model code works internally |
by the axes in the lower left of the figure the model code works internally |
69 |
in a locally orthoganal coordinate $(x,y,z)$. For this experiment description |
in a locally orthogonal coordinate $(x,y,z)$. For this experiment description |
70 |
the local orthogonal model coordinate $(x,y,z)$ is synonomous |
the local orthogonal model coordinate $(x,y,z)$ is synonymous |
71 |
with the coordinates $(\lambda,\varphi,r)$ shown in figure |
with the coordinates $(\lambda,\varphi,r)$ shown in figure |
72 |
\ref{fig:spherical-polar-coord} |
\ref{fig:spherical-polar-coord} |
73 |
\\ |
\\ |
120 |
\subsection{Equations solved} |
\subsection{Equations solved} |
121 |
For this problem |
For this problem |
122 |
the implicit free surface, {\bf HPE} (see section \ref{sec:hydrostatic_and_quasi-hydrostatic_forms}) form of the |
the implicit free surface, {\bf HPE} (see section \ref{sec:hydrostatic_and_quasi-hydrostatic_forms}) form of the |
123 |
equations described in Marshall et. al \cite{Marshall97a} are |
equations described in Marshall et. al \cite{marshall:97a} are |
124 |
employed. The flow is three-dimensional with just temperature, $\theta$, as |
employed. The flow is three-dimensional with just temperature, $\theta$, as |
125 |
an active tracer. The equation of state is linear. |
an active tracer. The equation of state is linear. |
126 |
A horizontal laplacian operator $\nabla_{h}^2$ provides viscous |
A horizontal Laplacian operator $\nabla_{h}^2$ provides viscous |
127 |
dissipation and provides a diffusive sub-grid scale closure for the |
dissipation and provides a diffusive sub-grid scale closure for the |
128 |
temperature equation. A wind-stress momentum forcing is added to the momentum |
temperature equation. A wind-stress momentum forcing is added to the momentum |
129 |
equation for the zonal flow, $u$. Other terms in the model |
equation for the zonal flow, $u$. Other terms in the model |
130 |
are explicitly switched off for this experiement configuration (see section |
are explicitly switched off for this experiment configuration (see section |
131 |
\ref{SEC:eg_fourl_code_config} ). This yields an active set of equations |
\ref{SEC:eg_fourl_code_config} ). This yields an active set of equations |
132 |
solved in this configuration, written in spherical polar coordinates as |
solved in this configuration, written in spherical polar coordinates as |
133 |
follows |
follows |
210 |
Vertically the |
Vertically the |
211 |
model is configured with four layers with constant depth, |
model is configured with four layers with constant depth, |
212 |
$\Delta z$, of $500$~m. The internal, locally orthogonal, model coordinate |
$\Delta z$, of $500$~m. The internal, locally orthogonal, model coordinate |
213 |
variables $x$ and $y$ are initialised from the values of |
variables $x$ and $y$ are initialized from the values of |
214 |
$\lambda$, $\varphi$, $\Delta \lambda$ and $\Delta \varphi$ in |
$\lambda$, $\varphi$, $\Delta \lambda$ and $\Delta \varphi$ in |
215 |
radians according to |
radians according to |
216 |
|
|
262 |
|
|
263 |
\subsubsection{Numerical Stability Criteria} |
\subsubsection{Numerical Stability Criteria} |
264 |
|
|
265 |
The laplacian viscosity coefficient, $A_{h}$, is set to $400 m s^{-1}$. |
The Laplacian viscosity coefficient, $A_{h}$, is set to $400 m s^{-1}$. |
266 |
This value is chosen to yield a Munk layer width, |
This value is chosen to yield a Munk layer width, |
267 |
|
|
268 |
\begin{eqnarray} |
\begin{eqnarray} |
279 |
|
|
280 |
\noindent The model is stepped forward with a |
\noindent The model is stepped forward with a |
281 |
time step $\delta t=1200$secs. With this time step the stability |
time step $\delta t=1200$secs. With this time step the stability |
282 |
parameter to the horizontal laplacian friction |
parameter to the horizontal Laplacian friction |
283 |
|
|
284 |
\begin{eqnarray} |
\begin{eqnarray} |
285 |
\label{EQ:laplacian_stability} |
\label{EQ:laplacian_stability} |
329 |
\\ |
\\ |
330 |
|
|
331 |
\noindent The stability parameter for internal gravity waves |
\noindent The stability parameter for internal gravity waves |
332 |
propogating at $2~{\rm m}~{\rm s}^{-1}$ |
propagating at $2~{\rm m}~{\rm s}^{-1}$ |
333 |
|
|
334 |
\begin{eqnarray} |
\begin{eqnarray} |
335 |
\label{EQ:igw_stability} |
\label{EQ:igw_stability} |
355 |
\item {\it code/SIZE.h}. |
\item {\it code/SIZE.h}. |
356 |
\end{itemize} |
\end{itemize} |
357 |
contain the code customisations and parameter settings for this |
contain the code customisations and parameter settings for this |
358 |
experiements. Below we describe the customisations |
experiments. Below we describe the customisations |
359 |
to these files associated with this experiment. |
to these files associated with this experiment. |
360 |
|
|
361 |
\subsubsection{File {\it input/data}} |
\subsubsection{File {\it input/data}} |
372 |
the initial and reference values of potential temperature at each model |
the initial and reference values of potential temperature at each model |
373 |
level in units of $^{\circ}$C. |
level in units of $^{\circ}$C. |
374 |
The entries are ordered from surface to depth. For each |
The entries are ordered from surface to depth. For each |
375 |
depth level the inital and reference profiles will be uniform in |
depth level the initial and reference profiles will be uniform in |
376 |
$x$ and $y$. The values specified here are read into the |
$x$ and $y$. The values specified here are read into the |
377 |
variable |
variable |
378 |
{\bf |
{\bf |
418 |
|
|
419 |
\item Line 6, |
\item Line 6, |
420 |
\begin{verbatim} viscAz=1.E-2, \end{verbatim} |
\begin{verbatim} viscAz=1.E-2, \end{verbatim} |
421 |
this line sets the vertical laplacian dissipation coefficient to |
this line sets the vertical Laplacian dissipation coefficient to |
422 |
$1 \times 10^{-2} {\rm m^{2}s^{-1}}$. Boundary conditions |
$1 \times 10^{-2} {\rm m^{2}s^{-1}}$. Boundary conditions |
423 |
for this operator are specified later. |
for this operator are specified later. |
424 |
The variable |
The variable |
438 |
\begin{rawhtml} <A href=../../../code_reference/vdb/names/PF.htm> \end{rawhtml} |
\begin{rawhtml} <A href=../../../code_reference/vdb/names/PF.htm> \end{rawhtml} |
439 |
viscAr |
viscAr |
440 |
\begin{rawhtml} </A>\end{rawhtml} |
\begin{rawhtml} </A>\end{rawhtml} |
441 |
}. At each time step, the viscous term contribution to the momentum eqautions |
}. At each time step, the viscous term contribution to the momentum equations |
442 |
is calculated in routine |
is calculated in routine |
443 |
{\it S/R CALC\_DIFFUSIVITY}. |
{\it S/R CALC\_DIFFUSIVITY}. |
444 |
|
|
697 |
\end{verbatim} |
\end{verbatim} |
698 |
This line requests that the simulation be performed in a |
This line requests that the simulation be performed in a |
699 |
spherical polar coordinate system. It affects the interpretation of |
spherical polar coordinate system. It affects the interpretation of |
700 |
grid inoput parameters, for exampl {\bf delX} and {\bf delY} and |
grid input parameters, for example {\bf delX} and {\bf delY} and |
701 |
causes the grid generation routines to initialise an internal grid based |
causes the grid generation routines to initialize an internal grid based |
702 |
on spherical polar geometry. |
on spherical polar geometry. |
703 |
The variable |
The variable |
704 |
{\bf |
{\bf |
733 |
This line sets the southern boundary of the modeled |
This line sets the southern boundary of the modeled |
734 |
domain to $0^{\circ}$ latitude. This value affects both the |
domain to $0^{\circ}$ latitude. This value affects both the |
735 |
generation of the locally orthogonal grid that the model |
generation of the locally orthogonal grid that the model |
736 |
uses internally and affects the initialisation of the coriolis force. |
uses internally and affects the initialization of the coriolis force. |
737 |
Note - it is not required to set |
Note - it is not required to set |
738 |
a longitude boundary, since the absolute longitude does |
a longitude boundary, since the absolute longitude does |
739 |
not alter the kernel equation discretisation. |
not alter the kernel equation discretisation. |
960 |
The {\it input/windx.sin\_y} file specifies a two-dimensional ($x,y$) |
The {\it input/windx.sin\_y} file specifies a two-dimensional ($x,y$) |
961 |
map of wind stress ,$\tau_{x}$, values. The units used are $Nm^{-2}$ (the |
map of wind stress ,$\tau_{x}$, values. The units used are $Nm^{-2}$ (the |
962 |
default for MITgcm). |
default for MITgcm). |
963 |
Although $\tau_{x}$ is only a function of latituted, $y$, |
Although $\tau_{x}$ is only a function of latitude, $y$, |
964 |
in this experiment |
in this experiment |
965 |
this file must still define a complete two-dimensional map in order |
this file must still define a complete two-dimensional map in order |
966 |
to be compatible with the standard code for loading forcing fields |
to be compatible with the standard code for loading forcing fields |
1061 |
% pwd |
% pwd |
1062 |
\end{verbatim} |
\end{verbatim} |
1063 |
|
|
1064 |
You shold see a response on the screen ending in |
You should see a response on the screen ending in |
1065 |
|
|
1066 |
{\it verification/exp2/input } |
{\it verification/exp2/input } |
1067 |
|
|