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\section{Introduction} |
This document provides the reader with the information necessary to |
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This documentation provides the reader with the information necessary to |
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carry out numerical experiments using MITgcm. It gives a comprehensive |
carry out numerical experiments using MITgcm. It gives a comprehensive |
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description of the continuous equations on which the model is based, the |
description of the continuous equations on which the model is based, the |
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numerical algorithms the model employs and a description of the associated |
numerical algorithms the model employs and a description of the associated |
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both process and general circulation studies of the atmosphere and ocean are |
both process and general circulation studies of the atmosphere and ocean are |
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also presented. |
also presented. |
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\section{Introduction} |
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\begin{rawhtml} |
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<!-- CMIREDIR:innovations: --> |
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\end{rawhtml} |
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MITgcm has a number of novel aspects: |
MITgcm has a number of novel aspects: |
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\begin{itemize} |
\begin{itemize} |
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\end{itemize} |
\end{itemize} |
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Key publications reporting on and charting the development of the model are |
Key publications reporting on and charting the development of the model are |
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listed in an Appendix. |
\cite{hill:95,marshall:97a,marshall:97b,adcroft:97,marshall:98,adcroft:99,hill:99,maro-eta:99}: |
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\begin{verbatim} |
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Hill, C. and J. Marshall, (1995) |
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Application of a Parallel Navier-Stokes Model to Ocean Circulation in |
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Parallel Computational Fluid Dynamics |
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In Proceedings of Parallel Computational Fluid Dynamics: Implementations |
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and Results Using Parallel Computers, 545-552. |
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Elsevier Science B.V.: New York |
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Marshall, J., C. Hill, L. Perelman, and A. Adcroft, (1997) |
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Hydrostatic, quasi-hydrostatic, and nonhydrostatic ocean modeling |
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J. Geophysical Res., 102(C3), 5733-5752. |
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Marshall, J., A. Adcroft, C. Hill, L. Perelman, and C. Heisey, (1997) |
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A finite-volume, incompressible Navier Stokes model for studies of the ocean |
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on parallel computers, |
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J. Geophysical Res., 102(C3), 5753-5766. |
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Adcroft, A.J., Hill, C.N. and J. Marshall, (1997) |
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Representation of topography by shaved cells in a height coordinate ocean |
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model |
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Mon Wea Rev, vol 125, 2293-2315 |
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Marshall, J., Jones, H. and C. Hill, (1998) |
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Efficient ocean modeling using non-hydrostatic algorithms |
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Journal of Marine Systems, 18, 115-134 |
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Adcroft, A., Hill C. and J. Marshall: (1999) |
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A new treatment of the Coriolis terms in C-grid models at both high and low |
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resolutions, |
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Mon. Wea. Rev. Vol 127, pages 1928-1936 |
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Hill, C, Adcroft,A., Jamous,D., and J. Marshall, (1999) |
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A Strategy for Terascale Climate Modeling. |
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In Proceedings of the Eighth ECMWF Workshop on the Use of Parallel Processors |
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in Meteorology, pages 406-425 |
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World Scientific Publishing Co: UK |
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Marotzke, J, Giering,R., Zhang, K.Q., Stammer,D., Hill,C., and T.Lee, (1999) |
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Construction of the adjoint MIT ocean general circulation model and |
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application to Atlantic heat transport variability |
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J. Geophysical Res., 104(C12), 29,529-29,547. |
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\end{verbatim} |
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We begin by briefly showing some of the results of the model in action to |
We begin by briefly showing some of the results of the model in action to |
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give a feel for the wide range of problems that can be addressed using it. |
give a feel for the wide range of problems that can be addressed using it. |
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numerical algorithm and implementation that lie behind these calculations is |
numerical algorithm and implementation that lie behind these calculations is |
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given later. Indeed many of the illustrative examples shown below can be |
given later. Indeed many of the illustrative examples shown below can be |
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easily reproduced: simply download the model (the minimum you need is a PC |
easily reproduced: simply download the model (the minimum you need is a PC |
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running linux, together with a FORTRAN\ 77 compiler) and follow the examples |
running Linux, together with a FORTRAN\ 77 compiler) and follow the examples |
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described in detail in the documentation. |
described in detail in the documentation. |
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\subsection{Global atmosphere: `Held-Suarez' benchmark} |
\subsection{Global atmosphere: `Held-Suarez' benchmark} |
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\begin{rawhtml} |
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<!-- CMIREDIR:atmospheric_example: --> |
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\end{rawhtml} |
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A novel feature of MITgcm is its ability to simulate, using one basic algorithm, |
A novel feature of MITgcm is its ability to simulate, using one basic algorithm, |
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both atmospheric and oceanographic flows at both small and large scales. |
both atmospheric and oceanographic flows at both small and large scales. |
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%% CNHend |
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As described in Adcroft (2001), a `cubed sphere' is used to discretize the |
As described in Adcroft (2001), a `cubed sphere' is used to discretize the |
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globe permitting a uniform gridding and obviated the need to Fourier filter. |
globe permitting a uniform griding and obviated the need to Fourier filter. |
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The `vector-invariant' form of MITgcm supports any orthogonal curvilinear |
The `vector-invariant' form of MITgcm supports any orthogonal curvilinear |
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grid, of which the cubed sphere is just one of many choices. |
grid, of which the cubed sphere is just one of many choices. |
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%% CNHend |
%% CNHend |
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\subsection{Ocean gyres} |
\subsection{Ocean gyres} |
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\begin{rawhtml} |
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<!-- CMIREDIR:oceanic_example: --> |
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\end{rawhtml} |
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\begin{rawhtml} |
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<!-- CMIREDIR:ocean_gyres: --> |
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\end{rawhtml} |
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Baroclinic instability is a ubiquitous process in the ocean, as well as the |
Baroclinic instability is a ubiquitous process in the ocean, as well as the |
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atmosphere. Ocean eddies play an important role in modifying the |
atmosphere. Ocean eddies play an important role in modifying the |
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visible. |
visible. |
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%% CNHbegin |
%% CNHbegin |
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\input{part1/ocean_gyres_figure} |
\input{part1/atl6_figure} |
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%% CNHend |
%% CNHend |
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\subsection{Global ocean circulation} |
\subsection{Global ocean circulation} |
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\begin{rawhtml} |
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<!-- CMIREDIR:global_ocean_circulation: --> |
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\end{rawhtml} |
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Figure \ref{fig:large-scale-circ} (top) shows the pattern of ocean currents at |
Figure \ref{fig:large-scale-circ} (top) shows the pattern of ocean currents at |
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the surface of a 4$^{\circ }$ |
the surface of a 4$^{\circ }$ |
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%%CNHend |
%%CNHend |
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\subsection{Convection and mixing over topography} |
\subsection{Convection and mixing over topography} |
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\begin{rawhtml} |
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<!-- CMIREDIR:mixing_over_topography: --> |
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\end{rawhtml} |
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Dense plumes generated by localized cooling on the continental shelf of the |
Dense plumes generated by localized cooling on the continental shelf of the |
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ocean may be influenced by rotation when the deformation radius is smaller |
ocean may be influenced by rotation when the deformation radius is smaller |
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than the width of the cooling region. Rather than gravity plumes, the |
than the width of the cooling region. Rather than gravity plumes, the |
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mechanism for moving dense fluid down the shelf is then through geostrophic |
mechanism for moving dense fluid down the shelf is then through geostrophic |
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eddies. The simulation shown in the figure \ref{fig::convect-and-topo} |
eddies. The simulation shown in the figure \ref{fig:convect-and-topo} |
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(blue is cold dense fluid, red is |
(blue is cold dense fluid, red is |
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warmer, lighter fluid) employs the non-hydrostatic capability of MITgcm to |
warmer, lighter fluid) employs the non-hydrostatic capability of MITgcm to |
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trigger convection by surface cooling. The cold, dense water falls down the |
trigger convection by surface cooling. The cold, dense water falls down the |
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%%CNHend |
%%CNHend |
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\subsection{Boundary forced internal waves} |
\subsection{Boundary forced internal waves} |
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\begin{rawhtml} |
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<!-- CMIREDIR:boundary_forced_internal_waves: --> |
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\end{rawhtml} |
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The unique ability of MITgcm to treat non-hydrostatic dynamics in the |
The unique ability of MITgcm to treat non-hydrostatic dynamics in the |
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presence of complex geometry makes it an ideal tool to study internal wave |
presence of complex geometry makes it an ideal tool to study internal wave |
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%%CNHend |
%%CNHend |
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\subsection{Parameter sensitivity using the adjoint of MITgcm} |
\subsection{Parameter sensitivity using the adjoint of MITgcm} |
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\begin{rawhtml} |
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<!-- CMIREDIR:parameter_sensitivity: --> |
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\end{rawhtml} |
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Forward and tangent linear counterparts of MITgcm are supported using an |
Forward and tangent linear counterparts of MITgcm are supported using an |
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`automatic adjoint compiler'. These can be used in parameter sensitivity and |
`automatic adjoint compiler'. These can be used in parameter sensitivity and |
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As one example of application of the MITgcm adjoint, Figure \ref{fig:hf-sensitivity} |
As one example of application of the MITgcm adjoint, Figure \ref{fig:hf-sensitivity} |
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maps the gradient $\frac{\partial J}{\partial \mathcal{H}}$where $J$ is the magnitude |
maps the gradient $\frac{\partial J}{\partial \mathcal{H}}$where $J$ is the magnitude |
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of the overturning streamfunction shown in figure \ref{fig:large-scale-circ} |
of the overturning stream-function shown in figure \ref{fig:large-scale-circ} |
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at 60$^{\circ }$N and $ |
at 60$^{\circ }$N and $ |
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\mathcal{H}(\lambda,\varphi)$ is the mean, local air-sea heat flux over |
\mathcal{H}(\lambda,\varphi)$ is the mean, local air-sea heat flux over |
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a 100 year period. We see that $J$ is |
a 100 year period. We see that $J$ is |
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%%CNHend |
%%CNHend |
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\subsection{Global state estimation of the ocean} |
\subsection{Global state estimation of the ocean} |
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\begin{rawhtml} |
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<!-- CMIREDIR:global_state_estimation: --> |
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\end{rawhtml} |
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An important application of MITgcm is in state estimation of the global |
An important application of MITgcm is in state estimation of the global |
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ocean circulation. An appropriately defined `cost function', which measures |
ocean circulation. An appropriately defined `cost function', which measures |
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the departure of the model from observations (both remotely sensed and |
the departure of the model from observations (both remotely sensed and |
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insitu) over an interval of time, is minimized by adjusting `control |
in-situ) over an interval of time, is minimized by adjusting `control |
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parameters' such as air-sea fluxes, the wind field, the initial conditions |
parameters' such as air-sea fluxes, the wind field, the initial conditions |
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etc. Figure \ref{fig:assimilated-globes} shows an estimate of the time-mean |
etc. Figure \ref{fig:assimilated-globes} shows the large scale planetary |
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surface elevation of the ocean obtained by bringing the model in to |
circulation and a Hopf-Muller plot of Equatorial sea-surface height. |
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Both are obtained from assimilation bringing the model in to |
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consistency with altimetric and in-situ observations over the period |
consistency with altimetric and in-situ observations over the period |
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1992-1997. {\bf CHANGE THIS TEXT - FIG FROM PATRICK/CARL/DETLEF} |
1992-1997. |
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%% CNHbegin |
%% CNHbegin |
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\input{part1/globes_figure} |
\input{part1/assim_figure} |
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%% CNHend |
%% CNHend |
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\subsection{Ocean biogeochemical cycles} |
\subsection{Ocean biogeochemical cycles} |
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\begin{rawhtml} |
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<!-- CMIREDIR:ocean_biogeo_cycles: --> |
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\end{rawhtml} |
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MITgcm is being used to study global biogeochemical cycles in the ocean. For |
MITgcm is being used to study global biogeochemical cycles in the ocean. For |
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example one can study the effects of interannual changes in meteorological |
example one can study the effects of interannual changes in meteorological |
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%%CNHend |
%%CNHend |
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\subsection{Simulations of laboratory experiments} |
\subsection{Simulations of laboratory experiments} |
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\begin{rawhtml} |
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<!-- CMIREDIR:classroom_exp: --> |
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\end{rawhtml} |
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Figure \ref{fig:lab-simulation} shows MITgcm being used to simulate a |
Figure \ref{fig:lab-simulation} shows MITgcm being used to simulate a |
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laboratory experiment enquiring in to the dynamics of the Antarctic Circumpolar Current (ACC). An |
laboratory experiment inquiring into the dynamics of the Antarctic Circumpolar Current (ACC). An |
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initially homogeneous tank of water ($1m$ in diameter) is driven from its |
initially homogeneous tank of water ($1m$ in diameter) is driven from its |
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free surface by a rotating heated disk. The combined action of mechanical |
free surface by a rotating heated disk. The combined action of mechanical |
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and thermal forcing creates a lens of fluid which becomes baroclinically |
and thermal forcing creates a lens of fluid which becomes baroclinically |
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% $Name$ |
% $Name$ |
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\section{Continuous equations in `r' coordinates} |
\section{Continuous equations in `r' coordinates} |
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\begin{rawhtml} |
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<!-- CMIREDIR:z-p_isomorphism: --> |
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\end{rawhtml} |
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To render atmosphere and ocean models from one dynamical core we exploit |
To render atmosphere and ocean models from one dynamical core we exploit |
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`isomorphisms' between equation sets that govern the evolution of the |
`isomorphisms' between equation sets that govern the evolution of the |
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and encoded. The model variables have different interpretations depending on |
and encoded. The model variables have different interpretations depending on |
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whether the atmosphere or ocean is being studied. Thus, for example, the |
whether the atmosphere or ocean is being studied. Thus, for example, the |
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vertical coordinate `$r$' is interpreted as pressure, $p$, if we are |
vertical coordinate `$r$' is interpreted as pressure, $p$, if we are |
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modeling the atmosphere (left hand side of figure \ref{fig:isomorphic-equations}) |
modeling the atmosphere (right hand side of figure \ref{fig:isomorphic-equations}) |
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and height, $z$, if we are modeling the ocean (right hand side of figure |
and height, $z$, if we are modeling the ocean (left hand side of figure |
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\ref{fig:isomorphic-equations}). |
\ref{fig:isomorphic-equations}). |
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%%CNHbegin |
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\input{part1/vertcoord_figure.tex} |
\input{part1/vertcoord_figure.tex} |
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%%CNHend |
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\begin{equation*} |
\begin{equation} |
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\frac{D\vec{\mathbf{v}_{h}}}{Dt}+\left( 2\vec{\Omega}\times \vec{\mathbf{v}} |
\frac{D\vec{\mathbf{v}_{h}}}{Dt}+\left( 2\vec{\Omega}\times \vec{\mathbf{v}} |
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\right) _{h}+\mathbf{\nabla }_{h}\phi =\mathcal{F}_{\vec{\mathbf{v}_{h}}} |
\right) _{h}+\mathbf{\nabla }_{h}\phi =\mathcal{F}_{\vec{\mathbf{v}_{h}}} |
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\text{ horizontal mtm} \label{eq:horizontal_mtm} |
\text{ horizontal mtm} \label{eq:horizontal_mtm} |
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\end{equation*} |
\end{equation} |
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\begin{equation} |
\begin{equation} |
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\frac{D\dot{r}}{Dt}+\widehat{k}\cdot \left( 2\vec{\Omega}\times \vec{\mathbf{ |
\frac{D\dot{r}}{Dt}+\widehat{k}\cdot \left( 2\vec{\Omega}\times \vec{\mathbf{ |
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\begin{equation} |
\begin{equation} |
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\frac{DS}{Dt}=\mathcal{Q}_{S}\text{ humidity/salinity} |
\frac{DS}{Dt}=\mathcal{Q}_{S}\text{ humidity/salinity} |
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\label{eq:humidtity_salt} |
\label{eq:humidity_salt} |
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\end{equation} |
\end{equation} |
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Here: |
Here: |
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at fixed and moving $r$ surfaces we set (see figure \ref{fig:zandp-vert-coord}): |
at fixed and moving $r$ surfaces we set (see figure \ref{fig:zandp-vert-coord}): |
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\begin{equation} |
\begin{equation} |
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\dot{r}=0atr=R_{fixed}(x,y)\text{ (ocean bottom, top of the atmosphere)} |
\dot{r}=0 \text{\ at\ } r=R_{fixed}(x,y)\text{ (ocean bottom, top of the atmosphere)} |
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\label{eq:fixedbc} |
\label{eq:fixedbc} |
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\end{equation} |
\end{equation} |
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\begin{equation} |
\begin{equation} |
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\dot{r}=\frac{Dr}{Dt}atr=R_{moving}\text{ \ |
\dot{r}=\frac{Dr}{Dt} \text{\ at\ } r=R_{moving}\text{ \ |
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(oceansurface,bottomoftheatmosphere)} \label{eq:movingbc} |
(ocean surface,bottom of the atmosphere)} \label{eq:movingbc} |
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\end{equation} |
\end{equation} |
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Here |
Here |
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atmosphere)} \label{eq:moving-bc-atmos} |
atmosphere)} \label{eq:moving-bc-atmos} |
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\end{eqnarray} |
\end{eqnarray} |
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Then the (hydrostatic form of) equations (\ref{eq:horizontal_mtm}-\ref{eq:humidity_slainty}) |
Then the (hydrostatic form of) equations |
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yields a consistent set of atmospheric equations which, for convenience, are written out in $p$ |
(\ref{eq:horizontal_mtm}-\ref{eq:humidity_salt}) yields a consistent |
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coordinates in Appendix Atmosphere - see eqs(\ref{eq:atmos-prime}). |
set of atmospheric equations which, for convenience, are written out |
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in $p$ coordinates in Appendix Atmosphere - see |
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eqs(\ref{eq:atmos-prime}). |
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\subsection{Ocean} |
\subsection{Ocean} |
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| 650 |
\end{eqnarray} |
\end{eqnarray} |
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where $\eta $ is the elevation of the free surface. |
where $\eta $ is the elevation of the free surface. |
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|
| 653 |
Then equations (\ref{eq:horizontal_mtm}-\ref{eq:humidity_slainty}) yield a consistent set |
Then equations (\ref{eq:horizontal_mtm}-\ref{eq:humidity_salt}) yield a consistent set |
| 654 |
of oceanic equations |
of oceanic equations |
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which, for convenience, are written out in $z$ coordinates in Appendix Ocean |
which, for convenience, are written out in $z$ coordinates in Appendix Ocean |
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- see eqs(\ref{eq:ocean-mom}) to (\ref{eq:ocean-salt}). |
- see eqs(\ref{eq:ocean-mom}) to (\ref{eq:ocean-salt}). |
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| 658 |
\subsection{Hydrostatic, Quasi-hydrostatic, Quasi-nonhydrostatic and |
\subsection{Hydrostatic, Quasi-hydrostatic, Quasi-nonhydrostatic and |
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Non-hydrostatic forms} |
Non-hydrostatic forms} |
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\begin{rawhtml} |
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<!-- CMIREDIR:non_hydrostatic: --> |
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\end{rawhtml} |
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Let us separate $\phi $ in to surface, hydrostatic and non-hydrostatic terms: |
Let us separate $\phi $ in to surface, hydrostatic and non-hydrostatic terms: |
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\phi (x,y,r)=\phi _{s}(x,y)+\phi _{hyd}(x,y,r)+\phi _{nh}(x,y,r) |
\phi (x,y,r)=\phi _{s}(x,y)+\phi _{hyd}(x,y,r)+\phi _{nh}(x,y,r) |
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\label{eq:phi-split} |
\label{eq:phi-split} |
| 670 |
\end{equation} |
\end{equation} |
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and write eq(\ref{eq:incompressible}) in the form: |
%and write eq(\ref{eq:incompressible}) in the form: |
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% ^- this eq is missing (jmc) ; replaced with: |
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and write eq( \ref{eq:horizontal_mtm}) in the form: |
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| 675 |
\begin{equation} |
\begin{equation} |
| 676 |
\frac{\partial \vec{\mathbf{v}_{h}}}{\partial t}+\mathbf{\nabla }_{h}\phi |
\frac{\partial \vec{\mathbf{v}_{h}}}{\partial t}+\mathbf{\nabla }_{h}\phi |
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| 1101 |
\subsection{Vector invariant form} |
\subsection{Vector invariant form} |
| 1102 |
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| 1103 |
For some purposes it is advantageous to write momentum advection in eq(\ref |
For some purposes it is advantageous to write momentum advection in |
| 1104 |
{eq:horizontal_mtm}) and (\ref{eq:vertical_mtm}) in the (so-called) `vector invariant' form: |
eq(\ref {eq:horizontal_mtm}) and (\ref{eq:vertical_mtm}) in the |
| 1105 |
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(so-called) `vector invariant' form: |
| 1106 |
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| 1107 |
\begin{equation} |
\begin{equation} |
| 1108 |
\frac{D\vec{\mathbf{v}}}{Dt}=\frac{\partial \vec{\mathbf{v}}}{\partial t} |
\frac{D\vec{\mathbf{v}}}{Dt}=\frac{\partial \vec{\mathbf{v}}}{\partial t} |
| 1213 |
surface ($\phi $ is imposed and $\omega \neq 0$). |
surface ($\phi $ is imposed and $\omega \neq 0$). |
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| 1215 |
\subsubsection{Splitting the geo-potential} |
\subsubsection{Splitting the geo-potential} |
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\label{sec:hpe-p-geo-potential-split} |
| 1217 |
|
|
| 1218 |
For the purposes of initialization and reducing round-off errors, the model |
For the purposes of initialization and reducing round-off errors, the model |
| 1219 |
deals with perturbations from reference (or ``standard'') profiles. For |
deals with perturbations from reference (or ``standard'') profiles. For |
| 1243 |
The final form of the HPE's in p coordinates is then: |
The final form of the HPE's in p coordinates is then: |
| 1244 |
\begin{eqnarray} |
\begin{eqnarray} |
| 1245 |
\frac{D\vec{\mathbf{v}}_{h}}{Dt}+f\hat{\mathbf{k}}\times \vec{\mathbf{v}} |
\frac{D\vec{\mathbf{v}}_{h}}{Dt}+f\hat{\mathbf{k}}\times \vec{\mathbf{v}} |
| 1246 |
_{h}+\mathbf{\nabla }_{p}\phi ^{\prime } &=&\vec{\mathbf{\mathcal{F}}} \label{eq:atmos-prime} \\ |
_{h}+\mathbf{\nabla }_{p}\phi ^{\prime } &=&\vec{\mathbf{\mathcal{F}}} |
| 1247 |
|
\label{eq:atmos-prime} \\ |
| 1248 |
\frac{\partial \phi ^{\prime }}{\partial p}+\alpha ^{\prime } &=&0 \\ |
\frac{\partial \phi ^{\prime }}{\partial p}+\alpha ^{\prime } &=&0 \\ |
| 1249 |
\mathbf{\nabla }_{p}\cdot \vec{\mathbf{v}}_{h}+\frac{\partial \omega }{ |
\mathbf{\nabla }_{p}\cdot \vec{\mathbf{v}}_{h}+\frac{\partial \omega }{ |
| 1250 |
\partial p} &=&0 \\ |
\partial p} &=&0 \\ |
| 1275 |
\label{eq:non-boussinesq} |
\label{eq:non-boussinesq} |
| 1276 |
\end{eqnarray} |
\end{eqnarray} |
| 1277 |
These equations permit acoustics modes, inertia-gravity waves, |
These equations permit acoustics modes, inertia-gravity waves, |
| 1278 |
non-hydrostatic motions, a geostrophic (Rossby) mode and a thermo-haline |
non-hydrostatic motions, a geostrophic (Rossby) mode and a thermohaline |
| 1279 |
mode. As written, they cannot be integrated forward consistently - if we |
mode. As written, they cannot be integrated forward consistently - if we |
| 1280 |
step $\rho $ forward in (\ref{eq-zns-cont}), the answer will not be |
step $\rho $ forward in (\ref{eq-zns-cont}), the answer will not be |
| 1281 |
consistent with that obtained by stepping (\ref{eq-zns-heat}) and (\ref |
consistent with that obtained by stepping (\ref{eq-zns-heat}) and (\ref |
| 1290 |
_{\theta ,S}\frac{Dp}{Dt} \label{EOSexpansion} |
_{\theta ,S}\frac{Dp}{Dt} \label{EOSexpansion} |
| 1291 |
\end{equation} |
\end{equation} |
| 1292 |
|
|
| 1293 |
Note that $\frac{\partial \rho }{\partial p}=\frac{1}{c_{s}^{2}}$ is the |
Note that $\frac{\partial \rho }{\partial p}=\frac{1}{c_{s}^{2}}$ is |
| 1294 |
reciprocal of the sound speed ($c_{s}$) squared. Substituting into \ref{eq-zns-cont} gives: |
the reciprocal of the sound speed ($c_{s}$) squared. Substituting into |
| 1295 |
|
\ref{eq-zns-cont} gives: |
| 1296 |
\begin{equation} |
\begin{equation} |
| 1297 |
\frac{1}{\rho c_{s}^{2}}\frac{Dp}{Dt}+\mathbf{\nabla }_{z}\cdot \vec{\mathbf{ |
\frac{1}{\rho c_{s}^{2}}\frac{Dp}{Dt}+\mathbf{\nabla }_{z}\cdot \vec{\mathbf{ |
| 1298 |
v}}+\partial _{z}w\approx 0 \label{eq-zns-pressure} |
v}}+\partial _{z}w\approx 0 \label{eq-zns-pressure} |