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%%%% \part{MIT GCM basics} |
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% Section: Overview |
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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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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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\item it can be used to study both atmospheric and oceanic phenomena; one |
\item it can be used to study both atmospheric and oceanic phenomena; one |
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hydrodynamical kernel is used to drive forward both atmospheric and oceanic |
hydrodynamical kernel is used to drive forward both atmospheric and oceanic |
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models - see fig.1% |
models - see fig \ref{fig:onemodel} |
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\marginpar{ |
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Fig.1 One model}\ref{fig:onemodel} |
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\item it has a non-hydrostatic capability and so can be used to study both |
\item it has a non-hydrostatic capability and so can be used to study both |
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small-scale and large scale processes - see fig.2% |
small-scale and large scale processes - see fig \ref{fig:all-scales} |
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\marginpar{ |
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Fig.2 All scales}\ref{fig:all-scales} |
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\item finite volume techniques are employed yielding an intuitive |
\item finite volume techniques are employed yielding an intuitive |
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discretization and support for the treatment of irregular geometries using |
discretization and support for the treatment of irregular geometries using |
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orthogonal curvilinear grids and shaved cells - see fig.3% |
orthogonal curvilinear grids and shaved cells - see fig \ref{fig:finite-volumes} |
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\marginpar{ |
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Fig.3 Finite volumes}\ref{fig:Finite volumes} |
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\item tangent linear and adjoint counterparts are automatically maintained |
\item tangent linear and adjoint counterparts are automatically maintained |
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along with the forward model, permitting sensitivity and optimization |
along with the forward model, permitting sensitivity and optimization |
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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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\pagebreak |
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% $Name$ |
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The MITgcm has been designed and used to model a wide range of phenomena, |
The MITgcm has been designed and used to model a wide range of phenomena, |
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from convection on the scale of meters in the ocean to the global pattern of |
from convection on the scale of meters in the ocean to the global pattern of |
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atmospheric winds - see fig.2\ref{fig:all-scales}. To give a flavor of the |
atmospheric winds - see figure \ref{fig:all-scales}. To give a flavor of the |
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kinds of problems the model has been used to study, we briefly describe some |
kinds of problems the model has been used to study, we briefly describe some |
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of them here. A more detailed description of the underlying formulation, |
of them here. A more detailed description of the underlying formulation, |
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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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A novel feature of MITgcm is its ability to simulate both atmospheric and |
A novel feature of MITgcm is its ability to simulate, using one basic algorithm, |
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oceanographic flows at both small and large scales. |
both atmospheric and oceanographic flows at both small and large scales. |
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Fig.E1a.\ref{fig:Held-Suarez} shows an instantaneous plot of the 500$mb$ |
Figure \ref{fig:eddy_cs} shows an instantaneous plot of the 500$mb$ |
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temperature field obtained using the atmospheric isomorph of MITgcm run at |
temperature field obtained using the atmospheric isomorph of MITgcm run at |
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2.8$^{\circ }$ resolution on the cubed sphere. We see cold air over the pole |
2.8$^{\circ }$ resolution on the cubed sphere. We see cold air over the pole |
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(blue) and warm air along an equatorial band (red). Fully developed |
(blue) and warm air along an equatorial band (red). Fully developed |
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in Held and Suarez; 1994 designed to test atmospheric hydrodynamical cores - |
in Held and Suarez; 1994 designed to test atmospheric hydrodynamical cores - |
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there are no mountains or land-sea contrast. |
there are no mountains or land-sea contrast. |
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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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Fig.E1b shows the 5-year mean, zonally averaged potential temperature, zonal |
Figure \ref{fig:hs_zave_u} shows the 5-year mean, zonally averaged zonal |
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wind and meridional overturning streamfunction from a 20-level version of |
wind from a 20-level configuration of |
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the model. It compares favorable with more conventional spatial |
the model. It compares favorable with more conventional spatial |
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discretization approaches. |
discretization approaches. The two plots show the field calculated using the |
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cube-sphere grid and the flow calculated using a regular, spherical polar |
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A regular spherical lat-lon grid can also be used. |
latitude-longitude grid. Both grids are supported within the model. |
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\subsection{Ocean gyres} |
\subsection{Ocean gyres} |
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increased until the baroclinic instability process is resolved, numerical |
increased until the baroclinic instability process is resolved, numerical |
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solutions of a different and much more realistic kind, can be obtained. |
solutions of a different and much more realistic kind, can be obtained. |
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Fig. ?.? shows the surface temperature and velocity field obtained from |
Figure \ref{fig:ocean-gyres} shows the surface temperature and velocity |
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MITgcm run at $\frac{1}{6}^{\circ }$ horizontal resolution on a $lat-lon$ |
field obtained from MITgcm run at $\frac{1}{6}^{\circ }$ horizontal |
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resolution on a $lat-lon$ |
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grid in which the pole has been rotated by 90$^{\circ }$ on to the equator |
grid in which the pole has been rotated by 90$^{\circ }$ on to the equator |
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(to avoid the converging of meridian in northern latitudes). 21 vertical |
(to avoid the converging of meridian in northern latitudes). 21 vertical |
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levels are used in the vertical with a `lopped cell' representation of |
levels are used in the vertical with a `lopped cell' representation of |
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topography. The development and propagation of anomalously warm and cold |
topography. The development and propagation of anomalously warm and cold |
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eddies can be clearly been seen in the Gulf Stream region. The transport of |
eddies can be clearly seen in the Gulf Stream region. The transport of |
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warm water northward by the mean flow of the Gulf Stream is also clearly |
warm water northward by the mean flow of the Gulf Stream is also clearly |
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visible. |
visible. |
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\subsection{Global ocean circulation} |
\subsection{Global ocean circulation} |
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Fig.E2a shows the pattern of ocean currents at the surface of a 4$^{\circ }$ |
Figure \ref{fig:large-scale-circ} (top) shows the pattern of ocean currents at |
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the surface of a 4$^{\circ }$ |
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global ocean model run with 15 vertical levels. Lopped cells are used to |
global ocean model run with 15 vertical levels. Lopped cells are used to |
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represent topography on a regular $lat-lon$ grid extending from 70$^{\circ |
represent topography on a regular $lat-lon$ grid extending from 70$^{\circ |
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}N $ to 70$^{\circ }S$. The model is driven using monthly-mean winds with |
}N $ to 70$^{\circ }S$. The model is driven using monthly-mean winds with |
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transfer properties of ocean eddies, convection and mixing is parameterized |
transfer properties of ocean eddies, convection and mixing is parameterized |
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in this model. |
in this model. |
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Fig.E2b shows the meridional overturning circulation of the global ocean in |
Figure \ref{fig:large-scale-circ} (bottom) shows the meridional overturning |
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Sverdrups. |
circulation of the global ocean in Sverdrups. |
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\subsection{Convection and mixing over topography} |
\subsection{Convection and mixing over topography} |
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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 (blue is cold dense fluid, red is |
eddies. The simulation shown in the figure \ref{fig:convect-and-topo} |
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(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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slope but is deflected along the slope by rotation. It is found that |
slope but is deflected along the slope by rotation. It is found that |
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strong, and replaced by lateral entrainment due to the baroclinic |
strong, and replaced by lateral entrainment due to the baroclinic |
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instability of the along-slope current. |
instability of the along-slope current. |
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\subsection{Boundary forced internal waves} |
\subsection{Boundary forced internal waves} |
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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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dynamics and mixing in oceanic canyons and ridges driven by large amplitude |
dynamics and mixing in oceanic canyons and ridges driven by large amplitude |
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barotropic tidal currents imposed through open boundary conditions. |
barotropic tidal currents imposed through open boundary conditions. |
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Fig. ?.? shows the influence of cross-slope topographic variations on |
Fig. \ref{fig:boundary-forced-wave} shows the influence of cross-slope |
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topographic variations on |
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internal wave breaking - the cross-slope velocity is in color, the density |
internal wave breaking - the cross-slope velocity is in color, the density |
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contoured. The internal waves are excited by application of open boundary |
contoured. The internal waves are excited by application of open boundary |
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conditions on the left.\ They propagate to the sloping boundary (represented |
conditions on the left. They propagate to the sloping boundary (represented |
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using MITgcm's finite volume spatial discretization) where they break under |
using MITgcm's finite volume spatial discretization) where they break under |
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nonhydrostatic dynamics. |
nonhydrostatic dynamics. |
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\subsection{Parameter sensitivity using the adjoint of MITgcm} |
\subsection{Parameter sensitivity using the adjoint of MITgcm} |
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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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data assimilation studies. |
data assimilation studies. |
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As one example of application of the MITgcm adjoint, Fig.E4 maps the |
As one example of application of the MITgcm adjoint, Figure \ref{fig:hf-sensitivity} |
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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 fig?.? at 40$^{\circ }$N and $% |
of the overturning stream-function shown in figure \ref{fig:large-scale-circ} |
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\mathcal{H}$ is the air-sea heat flux 100 years before. We see that $J$ is |
at 60$^{\circ }$N and $ |
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\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 |
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sensitive to heat fluxes over the Labrador Sea, one of the important sources |
sensitive to heat fluxes over the Labrador Sea, one of the important sources |
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of deep water for the thermohaline circulations. This calculation also |
of deep water for the thermohaline circulations. This calculation also |
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yields sensitivities to all other model parameters. |
yields sensitivities to all other model parameters. |
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\subsection{Global state estimation of the ocean} |
\subsection{Global state estimation of the ocean} |
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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 ?.? shows an estimate of the time-mean surface elevation of the |
etc. Figure \ref{fig:assimilated-globes} shows the large scale planetary |
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ocean obtained by bringing the model in to consistency with altimetric and |
circulation and a Hopf-Muller plot of Equatorial sea-surface height. |
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in-situ observations over the period 1992-1997. |
Both are obtained from assimilation bringing the model in to |
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consistency with altimetric and in-situ observations over the period |
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1992-1997. |
302 |
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303 |
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%% CNHbegin |
304 |
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\input{part1/assim_figure} |
305 |
|
%% CNHend |
306 |
|
|
307 |
\subsection{Ocean biogeochemical cycles} |
\subsection{Ocean biogeochemical cycles} |
308 |
|
|
309 |
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 |
310 |
example one can study the effects of interannual changes in meteorological |
example one can study the effects of interannual changes in meteorological |
311 |
forcing and upper ocean circulation on the fluxes of carbon dioxide and |
forcing and upper ocean circulation on the fluxes of carbon dioxide and |
312 |
oxygen between the ocean and atmosphere. The figure shows the annual air-sea |
oxygen between the ocean and atmosphere. Figure \ref{fig:biogeo} shows |
313 |
flux of oxygen and its relation to density outcrops in the southern oceans |
the annual air-sea flux of oxygen and its relation to density outcrops in |
314 |
from a single year of a global, interannually varying simulation. |
the southern oceans from a single year of a global, interannually varying |
315 |
|
simulation. The simulation is run at $1^{\circ}\times1^{\circ}$ resolution |
316 |
Chris - get figure here: http://puddle.mit.edu/\symbol{126}% |
telescoping to $\frac{1}{3}^{\circ}\times\frac{1}{3}^{\circ}$ in the tropics (not shown). |
317 |
mick/biogeochem.html |
|
318 |
|
%%CNHbegin |
319 |
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\input{part1/biogeo_figure} |
320 |
|
%%CNHend |
321 |
|
|
322 |
\subsection{Simulations of laboratory experiments} |
\subsection{Simulations of laboratory experiments} |
323 |
|
|
324 |
Figure ?.? shows MITgcm being used to simulate a laboratory experiment |
Figure \ref{fig:lab-simulation} shows MITgcm being used to simulate a |
325 |
enquiring in to the dynamics of the Antarctic Circumpolar Current (ACC). An |
laboratory experiment inquiring in to the dynamics of the Antarctic Circumpolar Current (ACC). An |
326 |
initially homogeneous tank of water ($1m$ in diameter) is driven from its |
initially homogeneous tank of water ($1m$ in diameter) is driven from its |
327 |
free surface by a rotating heated disk. The combined action of mechanical |
free surface by a rotating heated disk. The combined action of mechanical |
328 |
and thermal forcing creates a lens of fluid which becomes baroclinically |
and thermal forcing creates a lens of fluid which becomes baroclinically |
329 |
unstable. The stratification and depth of penetration of the lens is |
unstable. The stratification and depth of penetration of the lens is |
330 |
arrested by its instability in a process analogous to that whic sets the |
arrested by its instability in a process analogous to that which sets the |
331 |
stratification of the ACC. |
stratification of the ACC. |
332 |
|
|
333 |
|
%%CNHbegin |
334 |
|
\input{part1/lab_figure} |
335 |
|
%%CNHend |
336 |
|
|
337 |
% $Header$ |
% $Header$ |
338 |
% $Name$ |
% $Name$ |
339 |
|
|
341 |
|
|
342 |
To render atmosphere and ocean models from one dynamical core we exploit |
To render atmosphere and ocean models from one dynamical core we exploit |
343 |
`isomorphisms' between equation sets that govern the evolution of the |
`isomorphisms' between equation sets that govern the evolution of the |
344 |
respective fluids - see fig.4% |
respective fluids - see figure \ref{fig:isomorphic-equations}. |
345 |
\marginpar{ |
One system of hydrodynamical equations is written down |
|
Fig.4. Isomorphisms}. One system of hydrodynamical equations is written down |
|
346 |
and encoded. The model variables have different interpretations depending on |
and encoded. The model variables have different interpretations depending on |
347 |
whether the atmosphere or ocean is being studied. Thus, for example, the |
whether the atmosphere or ocean is being studied. Thus, for example, the |
348 |
vertical coordinate `$r$' is interpreted as pressure, $p$, if we are |
vertical coordinate `$r$' is interpreted as pressure, $p$, if we are |
349 |
modeling the atmosphere and height, $z$, if we are modeling the ocean. |
modeling the atmosphere (left hand side of figure \ref{fig:isomorphic-equations}) |
350 |
|
and height, $z$, if we are modeling the ocean (right hand side of figure |
351 |
|
\ref{fig:isomorphic-equations}). |
352 |
|
|
353 |
|
%%CNHbegin |
354 |
|
\input{part1/zandpcoord_figure.tex} |
355 |
|
%%CNHend |
356 |
|
|
357 |
The state of the fluid at any time is characterized by the distribution of |
The state of the fluid at any time is characterized by the distribution of |
358 |
velocity $\vec{\mathbf{v}}$, active tracers $\theta $ and $S$, a |
velocity $\vec{\mathbf{v}}$, active tracers $\theta $ and $S$, a |
360 |
depend on $\theta $, $S$, and $p$. The equations that govern the evolution |
depend on $\theta $, $S$, and $p$. The equations that govern the evolution |
361 |
of these fields, obtained by applying the laws of classical mechanics and |
of these fields, obtained by applying the laws of classical mechanics and |
362 |
thermodynamics to a Boussinesq, Navier-Stokes fluid are, written in terms of |
thermodynamics to a Boussinesq, Navier-Stokes fluid are, written in terms of |
363 |
a generic vertical coordinate, $r$, see fig.5% |
a generic vertical coordinate, $r$, so that the appropriate |
364 |
\marginpar{ |
kinematic boundary conditions can be applied isomorphically |
365 |
Fig.5 The vertical coordinate of model}: |
see figure \ref{fig:zandp-vert-coord}. |
366 |
|
|
367 |
|
%%CNHbegin |
368 |
|
\input{part1/vertcoord_figure.tex} |
369 |
|
%%CNHend |
370 |
|
|
371 |
\begin{equation*} |
\begin{equation*} |
372 |
\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}} |
373 |
\right) _{h}+\mathbf{\nabla }_{h}\phi =\mathcal{F}_{\vec{\mathbf{v}_{h}}}% |
\right) _{h}+\mathbf{\nabla }_{h}\phi =\mathcal{F}_{\vec{\mathbf{v}_{h}}} |
374 |
\text{ horizontal mtm} |
\text{ horizontal mtm} \label{eq:horizontal_mtm} |
375 |
\end{equation*} |
\end{equation*} |
376 |
|
|
377 |
\begin{equation*} |
\begin{equation} |
378 |
\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{ |
379 |
v}}\right) +\frac{\partial \phi }{\partial r}+b=\mathcal{F}_{\dot{r}}\text{ |
v}}\right) +\frac{\partial \phi }{\partial r}+b=\mathcal{F}_{\dot{r}}\text{ |
380 |
vertical mtm} |
vertical mtm} \label{eq:vertical_mtm} |
381 |
\end{equation*} |
\end{equation} |
382 |
|
|
383 |
\begin{equation} |
\begin{equation} |
384 |
\mathbf{\nabla }_{h}\cdot \vec{\mathbf{v}}_{h}+\frac{\partial \dot{r}}{% |
\mathbf{\nabla }_{h}\cdot \vec{\mathbf{v}}_{h}+\frac{\partial \dot{r}}{ |
385 |
\partial r}=0\text{ continuity} \label{eq:continuous} |
\partial r}=0\text{ continuity} \label{eq:continuity} |
386 |
\end{equation} |
\end{equation} |
387 |
|
|
388 |
\begin{equation*} |
\begin{equation} |
389 |
b=b(\theta ,S,r)\text{ equation of state} |
b=b(\theta ,S,r)\text{ equation of state} \label{eq:equation_of_state} |
390 |
\end{equation*} |
\end{equation} |
391 |
|
|
392 |
\begin{equation*} |
\begin{equation} |
393 |
\frac{D\theta }{Dt}=\mathcal{Q}_{\theta }\text{ potential temperature} |
\frac{D\theta }{Dt}=\mathcal{Q}_{\theta }\text{ potential temperature} |
394 |
\end{equation*} |
\label{eq:potential_temperature} |
395 |
|
\end{equation} |
396 |
|
|
397 |
\begin{equation*} |
\begin{equation} |
398 |
\frac{DS}{Dt}=\mathcal{Q}_{S}\text{ humidity/salinity} |
\frac{DS}{Dt}=\mathcal{Q}_{S}\text{ humidity/salinity} |
399 |
\end{equation*} |
\label{eq:humidity_salt} |
400 |
|
\end{equation} |
401 |
|
|
402 |
Here: |
Here: |
403 |
|
|
411 |
\end{equation*} |
\end{equation*} |
412 |
|
|
413 |
\begin{equation*} |
\begin{equation*} |
414 |
\mathbf{\nabla }=\mathbf{\nabla }_{h}+\widehat{k}\frac{\partial }{\partial r}% |
\mathbf{\nabla }=\mathbf{\nabla }_{h}+\widehat{k}\frac{\partial }{\partial r} |
415 |
\text{ is the `grad' operator} |
\text{ is the `grad' operator} |
416 |
\end{equation*} |
\end{equation*} |
417 |
with $\mathbf{\nabla }_{h}$ operating in the horizontal and $\widehat{k}% |
with $\mathbf{\nabla }_{h}$ operating in the horizontal and $\widehat{k} |
418 |
\frac{\partial }{\partial r}$ operating in the vertical, where $\widehat{k}$ |
\frac{\partial }{\partial r}$ operating in the vertical, where $\widehat{k}$ |
419 |
is a unit vector in the vertical |
is a unit vector in the vertical |
420 |
|
|
448 |
\end{equation*} |
\end{equation*} |
449 |
|
|
450 |
\begin{equation*} |
\begin{equation*} |
451 |
\mathcal{F}_{\vec{\mathbf{v}}}\text{ are forcing and dissipation of }\vec{% |
\mathcal{F}_{\vec{\mathbf{v}}}\text{ are forcing and dissipation of }\vec{ |
452 |
\mathbf{v}} |
\mathbf{v}} |
453 |
\end{equation*} |
\end{equation*} |
454 |
|
|
461 |
\end{equation*} |
\end{equation*} |
462 |
|
|
463 |
The $\mathcal{F}^{\prime }s$ and $\mathcal{Q}^{\prime }s$ are provided by |
The $\mathcal{F}^{\prime }s$ and $\mathcal{Q}^{\prime }s$ are provided by |
464 |
extensive `physics' packages for atmosphere and ocean described in Chapter 6. |
`physics' and forcing packages for atmosphere and ocean. These are described |
465 |
|
in later chapters. |
466 |
|
|
467 |
\subsection{Kinematic Boundary conditions} |
\subsection{Kinematic Boundary conditions} |
468 |
|
|
469 |
\subsubsection{vertical} |
\subsubsection{vertical} |
470 |
|
|
471 |
at fixed and moving $r$ surfaces we set (see fig.5): |
at fixed and moving $r$ surfaces we set (see figure \ref{fig:zandp-vert-coord}): |
472 |
|
|
473 |
\begin{equation} |
\begin{equation} |
474 |
\dot{r}=0atr=R_{fixed}(x,y)\text{ (ocean bottom, top of the atmosphere)} |
\dot{r}=0atr=R_{fixed}(x,y)\text{ (ocean bottom, top of the atmosphere)} |
477 |
|
|
478 |
\begin{equation} |
\begin{equation} |
479 |
\dot{r}=\frac{Dr}{Dt}atr=R_{moving}\text{ \ |
\dot{r}=\frac{Dr}{Dt}atr=R_{moving}\text{ \ |
480 |
(oceansurface,bottomoftheatmosphere)} \label{eq:movingbc} |
(ocean surface,bottom of the atmosphere)} \label{eq:movingbc} |
481 |
\end{equation} |
\end{equation} |
482 |
|
|
483 |
Here |
Here |
494 |
|
|
495 |
\begin{equation} |
\begin{equation} |
496 |
\vec{\mathbf{v}}\cdot \vec{\mathbf{n}}=0 \label{eq:noflow} |
\vec{\mathbf{v}}\cdot \vec{\mathbf{n}}=0 \label{eq:noflow} |
497 |
\end{equation}% |
\end{equation} |
498 |
where $\vec{\mathbf{n}}$ is the normal to a solid boundary. |
where $\vec{\mathbf{n}}$ is the normal to a solid boundary. |
499 |
|
|
500 |
\subsection{Atmosphere} |
\subsection{Atmosphere} |
501 |
|
|
502 |
In the atmosphere, see fig.5, we interpret: |
In the atmosphere, (see figure \ref{fig:zandp-vert-coord}), we interpret: |
503 |
|
|
504 |
\begin{equation} |
\begin{equation} |
505 |
r=p\text{ is the pressure} \label{eq:atmos-r} |
r=p\text{ is the pressure} \label{eq:atmos-r} |
531 |
|
|
532 |
\begin{equation*} |
\begin{equation*} |
533 |
T\text{ is absolute temperature} |
T\text{ is absolute temperature} |
534 |
\end{equation*}% |
\end{equation*} |
535 |
\begin{equation*} |
\begin{equation*} |
536 |
p\text{ is the pressure} |
p\text{ is the pressure} |
537 |
\end{equation*}% |
\end{equation*} |
538 |
\begin{eqnarray*} |
\begin{eqnarray*} |
539 |
&&z\text{ is the height of the pressure surface} \\ |
&&z\text{ is the height of the pressure surface} \\ |
540 |
&&g\text{ is the acceleration due to gravity} |
&&g\text{ is the acceleration due to gravity} |
544 |
the Exner function $\Pi (p)$ given by (see Appendix Atmosphere) |
the Exner function $\Pi (p)$ given by (see Appendix Atmosphere) |
545 |
\begin{equation} |
\begin{equation} |
546 |
\Pi (p)=c_{p}(\frac{p}{p_{c}})^{\kappa } \label{eq:exner} |
\Pi (p)=c_{p}(\frac{p}{p_{c}})^{\kappa } \label{eq:exner} |
547 |
\end{equation}% |
\end{equation} |
548 |
where $p_{c}$ is a reference pressure and $\kappa =R/c_{p}$ with $R$ the gas |
where $p_{c}$ is a reference pressure and $\kappa =R/c_{p}$ with $R$ the gas |
549 |
constant and $c_{p}$ the specific heat of air at constant pressure. |
constant and $c_{p}$ the specific heat of air at constant pressure. |
550 |
|
|
570 |
atmosphere)} \label{eq:moving-bc-atmos} |
atmosphere)} \label{eq:moving-bc-atmos} |
571 |
\end{eqnarray} |
\end{eqnarray} |
572 |
|
|
573 |
Then the (hydrostatic form of) eq(\ref{eq:continuous}) yields a consistent |
Then the (hydrostatic form of) equations (\ref{eq:horizontal_mtm}-\ref{eq:humidity_salt}) |
574 |
set of atmospheric equations which, for convenience, are written out in $p$ |
yields a consistent set of atmospheric equations which, for convenience, are written out in $p$ |
575 |
coordinates in Appendix Atmosphere - see eqs(\ref{eq:atmos-prime}). |
coordinates in Appendix Atmosphere - see eqs(\ref{eq:atmos-prime}). |
576 |
|
|
577 |
\subsection{Ocean} |
\subsection{Ocean} |
594 |
|
|
595 |
The surface of the ocean is given by: $R_{moving}=\eta $ |
The surface of the ocean is given by: $R_{moving}=\eta $ |
596 |
|
|
597 |
The position of the resting free surface of the ocean is given by $% |
The position of the resting free surface of the ocean is given by $ |
598 |
R_{o}=Z_{o}=0$. |
R_{o}=Z_{o}=0$. |
599 |
|
|
600 |
Boundary conditions are: |
Boundary conditions are: |
602 |
\begin{eqnarray} |
\begin{eqnarray} |
603 |
w &=&0~\text{at }r=R_{fixed}\text{ (ocean bottom)} \label{eq:fixed-bc-ocean} |
w &=&0~\text{at }r=R_{fixed}\text{ (ocean bottom)} \label{eq:fixed-bc-ocean} |
604 |
\\ |
\\ |
605 |
w &=&\frac{D\eta }{Dt}\text{ at }r=R_{moving}=\eta \text{ (ocean surface) % |
w &=&\frac{D\eta }{Dt}\text{ at }r=R_{moving}=\eta \text{ (ocean surface) |
606 |
\label{eq:moving-bc-ocean}} |
\label{eq:moving-bc-ocean}} |
607 |
\end{eqnarray} |
\end{eqnarray} |
608 |
where $\eta $ is the elevation of the free surface. |
where $\eta $ is the elevation of the free surface. |
609 |
|
|
610 |
Then eq(\ref{eq:continuous}) yields a consistent set of oceanic equations |
Then equations (\ref{eq:horizontal_mtm}-\ref{eq:humidity_salt}) yield a consistent set |
611 |
|
of oceanic equations |
612 |
which, for convenience, are written out in $z$ coordinates in Appendix Ocean |
which, for convenience, are written out in $z$ coordinates in Appendix Ocean |
613 |
- see eqs(\ref{eq:ocean-mom}) to (\ref{eq:ocean-salt}). |
- see eqs(\ref{eq:ocean-mom}) to (\ref{eq:ocean-salt}). |
614 |
|
|
620 |
\begin{equation} |
\begin{equation} |
621 |
\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) |
622 |
\label{eq:phi-split} |
\label{eq:phi-split} |
623 |
\end{equation}% |
\end{equation} |
624 |
and write eq(\ref{incompressible}a,b) in the form: |
and write eq(\ref{eq:incompressible}) in the form: |
625 |
|
|
626 |
\begin{equation} |
\begin{equation} |
627 |
\frac{\partial \vec{\mathbf{v}_{h}}}{\partial t}+\mathbf{\nabla }_{h}\phi |
\frac{\partial \vec{\mathbf{v}_{h}}}{\partial t}+\mathbf{\nabla }_{h}\phi |
634 |
\end{equation} |
\end{equation} |
635 |
|
|
636 |
\begin{equation} |
\begin{equation} |
637 |
\epsilon _{nh}\frac{\partial \dot{r}}{\partial t}+\frac{\partial \phi _{nh}}{% |
\epsilon _{nh}\frac{\partial \dot{r}}{\partial t}+\frac{\partial \phi _{nh}}{ |
638 |
\partial r}=G_{\dot{r}} \label{eq:mom-w} |
\partial r}=G_{\dot{r}} \label{eq:mom-w} |
639 |
\end{equation} |
\end{equation} |
640 |
Here $\epsilon _{nh}$ is a non-hydrostatic parameter. |
Here $\epsilon _{nh}$ is a non-hydrostatic parameter. |
641 |
|
|
642 |
The $\left( \vec{\mathbf{G}}_{\vec{v}},G_{\dot{r}}\right) $ in eq(\ref% |
The $\left( \vec{\mathbf{G}}_{\vec{v}},G_{\dot{r}}\right) $ in eq(\ref |
643 |
{eq:mom-h}) and (\ref{eq:mom-w}) represent advective, metric and Coriolis |
{eq:mom-h}) and (\ref{eq:mom-w}) represent advective, metric and Coriolis |
644 |
terms in the momentum equations. In spherical coordinates they take the form% |
terms in the momentum equations. In spherical coordinates they take the form |
645 |
\footnote{% |
\footnote{ |
646 |
In the hydrostatic primitive equations (\textbf{HPE}) all underlined terms |
In the hydrostatic primitive equations (\textbf{HPE}) all underlined terms |
647 |
in (\ref{eq:gu-speherical}), (\ref{eq:gv-spherical}) and (\ref% |
in (\ref{eq:gu-speherical}), (\ref{eq:gv-spherical}) and (\ref |
648 |
{eq:gw-spherical}) are omitted; the singly-underlined terms are included in |
{eq:gw-spherical}) are omitted; the singly-underlined terms are included in |
649 |
the quasi-hydrostatic model (\textbf{QH}). The fully non-hydrostatic model (% |
the quasi-hydrostatic model (\textbf{QH}). The fully non-hydrostatic model ( |
650 |
\textbf{NH}) includes all terms.} - see Marshall et al 1997a for a full |
\textbf{NH}) includes all terms.} - see Marshall et al 1997a for a full |
651 |
discussion: |
discussion: |
652 |
|
|
654 |
\left. |
\left. |
655 |
\begin{tabular}{l} |
\begin{tabular}{l} |
656 |
$G_{u}=-\vec{\mathbf{v}}.\nabla u$ \\ |
$G_{u}=-\vec{\mathbf{v}}.\nabla u$ \\ |
657 |
$-\left\{ \underline{\frac{u\dot{r}}{{r}}}-\frac{uv\tan lat}{{r}}\right\} $ |
$-\left\{ \underline{\frac{u\dot{r}}{{r}}}-\frac{uv\tan \varphi}{{r}}\right\} $ |
658 |
\\ |
\\ |
659 |
$-\left\{ -2\Omega v\sin lat+\underline{2\Omega \dot{r}\cos lat}\right\} $ |
$-\left\{ -2\Omega v\sin \varphi+\underline{2\Omega \dot{r}\cos \varphi}\right\} $ |
660 |
\\ |
\\ |
661 |
$+\mathcal{F}_{u}$% |
$+\mathcal{F}_{u}$ |
662 |
\end{tabular}% |
\end{tabular} |
663 |
\ \right\} \left\{ |
\ \right\} \left\{ |
664 |
\begin{tabular}{l} |
\begin{tabular}{l} |
665 |
\textit{advection} \\ |
\textit{advection} \\ |
666 |
\textit{metric} \\ |
\textit{metric} \\ |
667 |
\textit{Coriolis} \\ |
\textit{Coriolis} \\ |
668 |
\textit{\ Forcing/Dissipation}% |
\textit{\ Forcing/Dissipation} |
669 |
\end{tabular}% |
\end{tabular} |
670 |
\ \right. \qquad \label{eq:gu-speherical} |
\ \right. \qquad \label{eq:gu-speherical} |
671 |
\end{equation} |
\end{equation} |
672 |
|
|
674 |
\left. |
\left. |
675 |
\begin{tabular}{l} |
\begin{tabular}{l} |
676 |
$G_{v}=-\vec{\mathbf{v}}.\nabla v$ \\ |
$G_{v}=-\vec{\mathbf{v}}.\nabla v$ \\ |
677 |
$-\left\{ \underline{\frac{v\dot{r}}{{r}}}-\frac{u^{2}\tan lat}{{r}}\right\} |
$-\left\{ \underline{\frac{v\dot{r}}{{r}}}-\frac{u^{2}\tan \varphi}{{r}}\right\} |
678 |
$ \\ |
$ \\ |
679 |
$-\left\{ -2\Omega u\sin lat\right\} $ \\ |
$-\left\{ -2\Omega u\sin \varphi \right\} $ \\ |
680 |
$+\mathcal{F}_{v}$% |
$+\mathcal{F}_{v}$ |
681 |
\end{tabular}% |
\end{tabular} |
682 |
\ \right\} \left\{ |
\ \right\} \left\{ |
683 |
\begin{tabular}{l} |
\begin{tabular}{l} |
684 |
\textit{advection} \\ |
\textit{advection} \\ |
685 |
\textit{metric} \\ |
\textit{metric} \\ |
686 |
\textit{Coriolis} \\ |
\textit{Coriolis} \\ |
687 |
\textit{\ Forcing/Dissipation}% |
\textit{\ Forcing/Dissipation} |
688 |
\end{tabular}% |
\end{tabular} |
689 |
\ \right. \qquad \label{eq:gv-spherical} |
\ \right. \qquad \label{eq:gv-spherical} |
690 |
\end{equation}% |
\end{equation} |
691 |
\qquad \qquad \qquad \qquad \qquad |
\qquad \qquad \qquad \qquad \qquad |
692 |
|
|
693 |
\begin{equation} |
\begin{equation} |
695 |
\begin{tabular}{l} |
\begin{tabular}{l} |
696 |
$G_{\dot{r}}=-\underline{\underline{\vec{\mathbf{v}}.\nabla \dot{r}}}$ \\ |
$G_{\dot{r}}=-\underline{\underline{\vec{\mathbf{v}}.\nabla \dot{r}}}$ \\ |
697 |
$+\left\{ \underline{\frac{u^{_{^{2}}}+v^{2}}{{r}}}\right\} $ \\ |
$+\left\{ \underline{\frac{u^{_{^{2}}}+v^{2}}{{r}}}\right\} $ \\ |
698 |
${+}\underline{{2\Omega u\cos lat}}$ \\ |
${+}\underline{{2\Omega u\cos \varphi}}$ \\ |
699 |
$\underline{\underline{\mathcal{F}_{\dot{r}}}}$% |
$\underline{\underline{\mathcal{F}_{\dot{r}}}}$ |
700 |
\end{tabular}% |
\end{tabular} |
701 |
\ \right\} \left\{ |
\ \right\} \left\{ |
702 |
\begin{tabular}{l} |
\begin{tabular}{l} |
703 |
\textit{advection} \\ |
\textit{advection} \\ |
704 |
\textit{metric} \\ |
\textit{metric} \\ |
705 |
\textit{Coriolis} \\ |
\textit{Coriolis} \\ |
706 |
\textit{\ Forcing/Dissipation}% |
\textit{\ Forcing/Dissipation} |
707 |
\end{tabular}% |
\end{tabular} |
708 |
\ \right. \label{eq:gw-spherical} |
\ \right. \label{eq:gw-spherical} |
709 |
\end{equation}% |
\end{equation} |
710 |
\qquad \qquad \qquad \qquad \qquad |
\qquad \qquad \qquad \qquad \qquad |
711 |
|
|
712 |
In the above `${r}$' is the distance from the center of the earth and `$lat$% |
In the above `${r}$' is the distance from the center of the earth and `$\varphi$ |
713 |
' is latitude. |
' is latitude. |
714 |
|
|
715 |
Grad and div operators in spherical coordinates are defined in appendix |
Grad and div operators in spherical coordinates are defined in appendix |
716 |
OPERATORS.% |
OPERATORS. |
717 |
\marginpar{ |
|
718 |
Fig.6 Spherical polar coordinate system.} |
%%CNHbegin |
719 |
|
\input{part1/sphere_coord_figure.tex} |
720 |
|
%%CNHend |
721 |
|
|
722 |
\subsubsection{Shallow atmosphere approximation} |
\subsubsection{Shallow atmosphere approximation} |
723 |
|
|
727 |
Coriolis force is treated approximately and the shallow atmosphere |
Coriolis force is treated approximately and the shallow atmosphere |
728 |
approximation is made.\ The MITgcm need not make the `traditional |
approximation is made.\ The MITgcm need not make the `traditional |
729 |
approximation'. To be able to support consistent non-hydrostatic forms the |
approximation'. To be able to support consistent non-hydrostatic forms the |
730 |
shallow atmosphere approximation can be relaxed - when dividing through by $% |
shallow atmosphere approximation can be relaxed - when dividing through by $ |
731 |
r $ in, for example, (\ref{eq:gu-speherical}), we do not replace $r$ by $a$, |
r $ in, for example, (\ref{eq:gu-speherical}), we do not replace $r$ by $a$, |
732 |
the radius of the earth. |
the radius of the earth. |
733 |
|
|
734 |
\subsubsection{Hydrostatic and quasi-hydrostatic forms} |
\subsubsection{Hydrostatic and quasi-hydrostatic forms} |
735 |
|
\label{sec:hydrostatic_and_quasi-hydrostatic_forms} |
736 |
|
|
737 |
These are discussed at length in Marshall et al (1997a). |
These are discussed at length in Marshall et al (1997a). |
738 |
|
|
741 |
are neglected and `${r}$' is replaced by `$a$', the mean radius of the |
are neglected and `${r}$' is replaced by `$a$', the mean radius of the |
742 |
earth. Once the pressure is found at one level - e.g. by inverting a 2-d |
earth. Once the pressure is found at one level - e.g. by inverting a 2-d |
743 |
Elliptic equation for $\phi _{s}$ at $r=R_{moving}$ - the pressure can be |
Elliptic equation for $\phi _{s}$ at $r=R_{moving}$ - the pressure can be |
744 |
computed at all other levels by integration of the hydrostatic relation, eq(% |
computed at all other levels by integration of the hydrostatic relation, eq( |
745 |
\ref{eq:hydrostatic}). |
\ref{eq:hydrostatic}). |
746 |
|
|
747 |
In the `quasi-hydrostatic' equations (\textbf{QH)} strict balance between |
In the `quasi-hydrostatic' equations (\textbf{QH)} strict balance between |
748 |
gravity and vertical pressure gradients is not imposed. The $2\Omega u\cos |
gravity and vertical pressure gradients is not imposed. The $2\Omega u\cos |
749 |
\phi $ Coriolis term are not neglected and are balanced by a non-hydrostatic |
\varphi $ Coriolis term are not neglected and are balanced by a non-hydrostatic |
750 |
contribution to the pressure field: only the terms underlined twice in Eqs. (% |
contribution to the pressure field: only the terms underlined twice in Eqs. ( |
751 |
\ref{eq:gu-speherical}$\rightarrow $\ \ref{eq:gw-spherical}) are set to zero |
\ref{eq:gu-speherical}$\rightarrow $\ \ref{eq:gw-spherical}) are set to zero |
752 |
and, simultaneously, the shallow atmosphere approximation is relaxed. In |
and, simultaneously, the shallow atmosphere approximation is relaxed. In |
753 |
\textbf{QH}\ \textit{all} the metric terms are retained and the full |
\textbf{QH}\ \textit{all} the metric terms are retained and the full |
755 |
vertical momentum equation (\ref{eq:mom-w}) becomes: |
vertical momentum equation (\ref{eq:mom-w}) becomes: |
756 |
|
|
757 |
\begin{equation*} |
\begin{equation*} |
758 |
\frac{\partial \phi _{nh}}{\partial r}=2\Omega u\cos lat |
\frac{\partial \phi _{nh}}{\partial r}=2\Omega u\cos \varphi |
759 |
\end{equation*} |
\end{equation*} |
760 |
making a small correction to the hydrostatic pressure. |
making a small correction to the hydrostatic pressure. |
761 |
|
|
771 |
|
|
772 |
\paragraph{Non-hydrostatic Ocean} |
\paragraph{Non-hydrostatic Ocean} |
773 |
|
|
774 |
In the non-hydrostatic ocean model all terms in equations Eqs.(\ref% |
In the non-hydrostatic ocean model all terms in equations Eqs.(\ref |
775 |
{eq:gu-speherical} $\rightarrow $\ \ref{eq:gw-spherical}) are retained. A |
{eq:gu-speherical} $\rightarrow $\ \ref{eq:gw-spherical}) are retained. A |
776 |
three dimensional elliptic equation must be solved subject to Neumann |
three dimensional elliptic equation must be solved subject to Neumann |
777 |
boundary conditions (see below). It is important to note that use of the |
boundary conditions (see below). It is important to note that use of the |
778 |
full \textbf{NH} does not admit any new `fast' waves in to the system - the |
full \textbf{NH} does not admit any new `fast' waves in to the system - the |
779 |
incompressible condition eq(\ref{eq:continuous})c has already filtered out |
incompressible condition eq(\ref{eq:continuity}) has already filtered out |
780 |
acoustic modes. It does, however, ensure that the gravity waves are treated |
acoustic modes. It does, however, ensure that the gravity waves are treated |
781 |
accurately with an exact dispersion relation. The \textbf{NH} set has a |
accurately with an exact dispersion relation. The \textbf{NH} set has a |
782 |
complete angular momentum principle and consistent energetics - see White |
complete angular momentum principle and consistent energetics - see White |
784 |
|
|
785 |
\paragraph{Quasi-nonhydrostatic Atmosphere} |
\paragraph{Quasi-nonhydrostatic Atmosphere} |
786 |
|
|
787 |
In the non-hydrostatic version of our atmospheric model we approximate $\dot{% |
In the non-hydrostatic version of our atmospheric model we approximate $\dot{ |
788 |
r}$ in the vertical momentum eqs(\ref{eq:mom-w}) and (\ref{eq:gv-spherical}) |
r}$ in the vertical momentum eqs(\ref{eq:mom-w}) and (\ref{eq:gv-spherical}) |
789 |
(but only here) by: |
(but only here) by: |
790 |
|
|
791 |
\begin{equation} |
\begin{equation} |
792 |
\dot{r}=\frac{Dp}{Dt}=\frac{1}{g}\frac{D\phi }{Dt} \label{eq:quasi-nh-w} |
\dot{r}=\frac{Dp}{Dt}=\frac{1}{g}\frac{D\phi }{Dt} \label{eq:quasi-nh-w} |
793 |
\end{equation}% |
\end{equation} |
794 |
where $p_{hy}$ is the hydrostatic pressure. |
where $p_{hy}$ is the hydrostatic pressure. |
795 |
|
|
796 |
\subsubsection{Summary of equation sets supported by model} |
\subsubsection{Summary of equation sets supported by model} |
818 |
|
|
819 |
\subparagraph{Non-hydrostatic} |
\subparagraph{Non-hydrostatic} |
820 |
|
|
821 |
Non-hydrostatic forms of the incompressible Boussinesq equations in $z-$% |
Non-hydrostatic forms of the incompressible Boussinesq equations in $z-$ |
822 |
coordinates are supported - see eqs(\ref{eq:ocean-mom}) to (\ref% |
coordinates are supported - see eqs(\ref{eq:ocean-mom}) to (\ref |
823 |
{eq:ocean-salt}). |
{eq:ocean-salt}). |
824 |
|
|
825 |
\subsection{Solution strategy} |
\subsection{Solution strategy} |
826 |
|
|
827 |
The method of solution employed in the \textbf{HPE}, \textbf{QH} and \textbf{% |
The method of solution employed in the \textbf{HPE}, \textbf{QH} and \textbf{ |
828 |
NH} models is summarized in Fig.7.% |
NH} models is summarized in Figure \ref{fig:solution-strategy}. |
829 |
\marginpar{ |
Under all dynamics, a 2-d elliptic equation is |
|
Fig.7 Solution strategy} Under all dynamics, a 2-d elliptic equation is |
|
830 |
first solved to find the surface pressure and the hydrostatic pressure at |
first solved to find the surface pressure and the hydrostatic pressure at |
831 |
any level computed from the weight of fluid above. Under \textbf{HPE} and |
any level computed from the weight of fluid above. Under \textbf{HPE} and |
832 |
\textbf{QH} dynamics, the horizontal momentum equations are then stepped |
\textbf{QH} dynamics, the horizontal momentum equations are then stepped |
835 |
stepping forward the horizontal momentum equations; $\dot{r}$ is found by |
stepping forward the horizontal momentum equations; $\dot{r}$ is found by |
836 |
stepping forward the vertical momentum equation. |
stepping forward the vertical momentum equation. |
837 |
|
|
838 |
|
%%CNHbegin |
839 |
|
\input{part1/solution_strategy_figure.tex} |
840 |
|
%%CNHend |
841 |
|
|
842 |
There is no penalty in implementing \textbf{QH} over \textbf{HPE} except, of |
There is no penalty in implementing \textbf{QH} over \textbf{HPE} except, of |
843 |
course, some complication that goes with the inclusion of $\cos \phi \ $% |
course, some complication that goes with the inclusion of $\cos \varphi \ $ |
844 |
Coriolis terms and the relaxation of the shallow atmosphere approximation. |
Coriolis terms and the relaxation of the shallow atmosphere approximation. |
845 |
But this leads to negligible increase in computation. In \textbf{NH}, in |
But this leads to negligible increase in computation. In \textbf{NH}, in |
846 |
contrast, one additional elliptic equation - a three-dimensional one - must |
contrast, one additional elliptic equation - a three-dimensional one - must |
850 |
hydrostatic limit, is as computationally economic as the \textbf{HPEs}. |
hydrostatic limit, is as computationally economic as the \textbf{HPEs}. |
851 |
|
|
852 |
\subsection{Finding the pressure field} |
\subsection{Finding the pressure field} |
853 |
|
\label{sec:finding_the_pressure_field} |
854 |
|
|
855 |
Unlike the prognostic variables $u$, $v$, $w$, $\theta $ and $S$, the |
Unlike the prognostic variables $u$, $v$, $w$, $\theta $ and $S$, the |
856 |
pressure field must be obtained diagnostically. We proceed, as before, by |
pressure field must be obtained diagnostically. We proceed, as before, by |
865 |
vertically from $r=R_{o}$ where $\phi _{hyd}(r=R_{o})=0$, to yield: |
vertically from $r=R_{o}$ where $\phi _{hyd}(r=R_{o})=0$, to yield: |
866 |
|
|
867 |
\begin{equation*} |
\begin{equation*} |
868 |
\int_{r}^{R_{o}}\frac{\partial \phi _{hyd}}{\partial r}dr=\left[ \phi _{hyd}% |
\int_{r}^{R_{o}}\frac{\partial \phi _{hyd}}{\partial r}dr=\left[ \phi _{hyd} |
869 |
\right] _{r}^{R_{o}}=\int_{r}^{R_{o}}-bdr |
\right] _{r}^{R_{o}}=\int_{r}^{R_{o}}-bdr |
870 |
\end{equation*} |
\end{equation*} |
871 |
and so |
and so |
883 |
|
|
884 |
\subsubsection{Surface pressure} |
\subsubsection{Surface pressure} |
885 |
|
|
886 |
The surface pressure equation can be obtained by integrating continuity, (% |
The surface pressure equation can be obtained by integrating continuity, |
887 |
\ref{eq:continuous})c, vertically from $r=R_{fixed}$ to $r=R_{moving}$ |
(\ref{eq:continuity}), vertically from $r=R_{fixed}$ to $r=R_{moving}$ |
888 |
|
|
889 |
\begin{equation*} |
\begin{equation*} |
890 |
\int_{R_{fixed}}^{R_{moving}}\left( \mathbf{\nabla }_{h}\cdot \vec{\mathbf{v}% |
\int_{R_{fixed}}^{R_{moving}}\left( \mathbf{\nabla }_{h}\cdot \vec{\mathbf{v} |
891 |
}_{h}+\partial _{r}\dot{r}\right) dr=0 |
}_{h}+\partial _{r}\dot{r}\right) dr=0 |
892 |
\end{equation*} |
\end{equation*} |
893 |
|
|
895 |
|
|
896 |
\begin{equation*} |
\begin{equation*} |
897 |
\frac{\partial \eta }{\partial t}+\vec{\mathbf{v}}.\nabla \eta |
\frac{\partial \eta }{\partial t}+\vec{\mathbf{v}}.\nabla \eta |
898 |
+\int_{R_{fixed}}^{R_{moving}}\mathbf{\nabla }_{h}\cdot \vec{\mathbf{v}}% |
+\int_{R_{fixed}}^{R_{moving}}\mathbf{\nabla }_{h}\cdot \vec{\mathbf{v}} |
899 |
_{h}dr=0 |
_{h}dr=0 |
900 |
\end{equation*} |
\end{equation*} |
901 |
where $\eta =R_{moving}-R_{o}$ is the free-surface $r$-anomaly in units of $% |
where $\eta =R_{moving}-R_{o}$ is the free-surface $r$-anomaly in units of $ |
902 |
r $. The above can be rearranged to yield, using Leibnitz's theorem: |
r $. The above can be rearranged to yield, using Leibnitz's theorem: |
903 |
|
|
904 |
\begin{equation} |
\begin{equation} |
905 |
\frac{\partial \eta }{\partial t}+\mathbf{\nabla }_{h}\cdot |
\frac{\partial \eta }{\partial t}+\mathbf{\nabla }_{h}\cdot |
906 |
\int_{R_{fixed}}^{R_{moving}}\vec{\mathbf{v}}_{h}dr=\text{source} |
\int_{R_{fixed}}^{R_{moving}}\vec{\mathbf{v}}_{h}dr=\text{source} |
907 |
\label{eq:free-surface} |
\label{eq:free-surface} |
908 |
\end{equation}% |
\end{equation} |
909 |
where we have incorporated a source term. |
where we have incorporated a source term. |
910 |
|
|
911 |
Whether $\phi $ is pressure (ocean model, $p/\rho _{c}$) or geopotential |
Whether $\phi $ is pressure (ocean model, $p/\rho _{c}$) or geopotential |
912 |
(atmospheric model), in (\ref{mtm-split}), the horizontal gradient term can |
(atmospheric model), in (\ref{eq:mom-h}), the horizontal gradient term can |
913 |
be written |
be written |
914 |
\begin{equation} |
\begin{equation} |
915 |
\mathbf{\nabla }_{h}\phi _{s}=\mathbf{\nabla }_{h}\left( b_{s}\eta \right) |
\mathbf{\nabla }_{h}\phi _{s}=\mathbf{\nabla }_{h}\left( b_{s}\eta \right) |
916 |
\label{eq:phi-surf} |
\label{eq:phi-surf} |
917 |
\end{equation}% |
\end{equation} |
918 |
where $b_{s}$ is the buoyancy at the surface. |
where $b_{s}$ is the buoyancy at the surface. |
919 |
|
|
920 |
In the hydrostatic limit ($\epsilon _{nh}=0$), Eqs(\ref{eq:mom-h}), (\ref% |
In the hydrostatic limit ($\epsilon _{nh}=0$), equations (\ref{eq:mom-h}), (\ref |
921 |
{eq:free-surface}) and (\ref{eq:phi-surf}) can be solved by inverting a 2-d |
{eq:free-surface}) and (\ref{eq:phi-surf}) can be solved by inverting a 2-d |
922 |
elliptic equation for $\phi _{s}$ as described in Chapter 2. Both `free |
elliptic equation for $\phi _{s}$ as described in Chapter 2. Both `free |
923 |
surface' and `rigid lid' approaches are available. |
surface' and `rigid lid' approaches are available. |
924 |
|
|
925 |
\subsubsection{Non-hydrostatic pressure} |
\subsubsection{Non-hydrostatic pressure} |
926 |
|
|
927 |
Taking the horizontal divergence of (\ref{hor-mtm}) and adding $\frac{% |
Taking the horizontal divergence of (\ref{eq:mom-h}) and adding |
928 |
\partial }{\partial r}$ of (\ref{vertmtm}), invoking the continuity equation |
$\frac{\partial }{\partial r}$ of (\ref{eq:mom-w}), invoking the continuity equation |
929 |
(\ref{incompressible}), we deduce that: |
(\ref{eq:continuity}), we deduce that: |
930 |
|
|
931 |
\begin{equation} |
\begin{equation} |
932 |
\nabla _{3}^{2}\phi _{nh}=\nabla .\vec{\mathbf{G}}_{\vec{v}}-\left( \mathbf{% |
\nabla _{3}^{2}\phi _{nh}=\nabla .\vec{\mathbf{G}}_{\vec{v}}-\left( \mathbf{ |
933 |
\nabla }_{h}^{2}\phi _{s}+\mathbf{\nabla }^{2}\phi _{hyd}\right) =\nabla .% |
\nabla }_{h}^{2}\phi _{s}+\mathbf{\nabla }^{2}\phi _{hyd}\right) =\nabla . |
934 |
\vec{\mathbf{F}} \label{eq:3d-invert} |
\vec{\mathbf{F}} \label{eq:3d-invert} |
935 |
\end{equation} |
\end{equation} |
936 |
|
|
950 |
\end{equation} |
\end{equation} |
951 |
where $\widehat{n}$ is a vector of unit length normal to the boundary. The |
where $\widehat{n}$ is a vector of unit length normal to the boundary. The |
952 |
kinematic condition (\ref{nonormalflow}) is also applied to the vertical |
kinematic condition (\ref{nonormalflow}) is also applied to the vertical |
953 |
velocity at $r=R_{moving}$. No-slip $\left( v_{T}=0\right) \ $or slip $% |
velocity at $r=R_{moving}$. No-slip $\left( v_{T}=0\right) \ $or slip $ |
954 |
\left( \partial v_{T}/\partial n=0\right) \ $conditions are employed on the |
\left( \partial v_{T}/\partial n=0\right) \ $conditions are employed on the |
955 |
tangential component of velocity, $v_{T}$, at all solid boundaries, |
tangential component of velocity, $v_{T}$, at all solid boundaries, |
956 |
depending on the form chosen for the dissipative terms in the momentum |
depending on the form chosen for the dissipative terms in the momentum |
957 |
equations - see below. |
equations - see below. |
958 |
|
|
959 |
Eq.(\ref{nonormalflow}) implies, making use of (\ref{mtm-split}), that: |
Eq.(\ref{nonormalflow}) implies, making use of (\ref{eq:mom-h}), that: |
960 |
|
|
961 |
\begin{equation} |
\begin{equation} |
962 |
\widehat{n}.\nabla \phi _{nh}=\widehat{n}.\vec{\mathbf{F}} |
\widehat{n}.\nabla \phi _{nh}=\widehat{n}.\vec{\mathbf{F}} |
967 |
\begin{equation*} |
\begin{equation*} |
968 |
\vec{\mathbf{F}}=\vec{\mathbf{G}}_{\vec{v}}-\left( \mathbf{\nabla }_{h}\phi |
\vec{\mathbf{F}}=\vec{\mathbf{G}}_{\vec{v}}-\left( \mathbf{\nabla }_{h}\phi |
969 |
_{s}+\mathbf{\nabla }\phi _{hyd}\right) |
_{s}+\mathbf{\nabla }\phi _{hyd}\right) |
970 |
\end{equation*}% |
\end{equation*} |
971 |
presenting inhomogeneous Neumann boundary conditions to the Elliptic problem |
presenting inhomogeneous Neumann boundary conditions to the Elliptic problem |
972 |
(\ref{eq:3d-invert}). As shown, for example, by Williams (1969), one can |
(\ref{eq:3d-invert}). As shown, for example, by Williams (1969), one can |
973 |
exploit classical 3D potential theory and, by introducing an appropriately |
exploit classical 3D potential theory and, by introducing an appropriately |
974 |
chosen $\delta $-function sheet of `source-charge', replace the |
chosen $\delta $-function sheet of `source-charge', replace the |
975 |
inhomogeneous boundary condition on pressure by a homogeneous one. The |
inhomogeneous boundary condition on pressure by a homogeneous one. The |
976 |
source term $rhs$ in (\ref{eq:3d-invert}) is the divergence of the vector $% |
source term $rhs$ in (\ref{eq:3d-invert}) is the divergence of the vector $ |
977 |
\vec{\mathbf{F}}.$ By simultaneously setting $% |
\vec{\mathbf{F}}.$ By simultaneously setting $ |
978 |
\begin{array}{l} |
\begin{array}{l} |
979 |
\widehat{n}.\vec{\mathbf{F}}% |
\widehat{n}.\vec{\mathbf{F}} |
980 |
\end{array}% |
\end{array} |
981 |
=0$\ and $\widehat{n}.\nabla \phi _{nh}=0\ $on the boundary the following |
=0$\ and $\widehat{n}.\nabla \phi _{nh}=0\ $on the boundary the following |
982 |
self-consistent but simpler homogenized Elliptic problem is obtained: |
self-consistent but simpler homogenized Elliptic problem is obtained: |
983 |
|
|
984 |
\begin{equation*} |
\begin{equation*} |
985 |
\nabla ^{2}\phi _{nh}=\nabla .\widetilde{\vec{\mathbf{F}}}\qquad |
\nabla ^{2}\phi _{nh}=\nabla .\widetilde{\vec{\mathbf{F}}}\qquad |
986 |
\end{equation*}% |
\end{equation*} |
987 |
where $\widetilde{\vec{\mathbf{F}}}$ is a modified $\vec{\mathbf{F}}$ such |
where $\widetilde{\vec{\mathbf{F}}}$ is a modified $\vec{\mathbf{F}}$ such |
988 |
that $\widetilde{\vec{\mathbf{F}}}.\widehat{n}=0$. As is implied by (\ref% |
that $\widetilde{\vec{\mathbf{F}}}.\widehat{n}=0$. As is implied by (\ref |
989 |
{eq:inhom-neumann-nh}) the modified boundary condition becomes: |
{eq:inhom-neumann-nh}) the modified boundary condition becomes: |
990 |
|
|
991 |
\begin{equation} |
\begin{equation} |
996 |
converges rapidly because $\phi _{nh}\ $is then only a small correction to |
converges rapidly because $\phi _{nh}\ $is then only a small correction to |
997 |
the hydrostatic pressure field (see the discussion in Marshall et al, a,b). |
the hydrostatic pressure field (see the discussion in Marshall et al, a,b). |
998 |
|
|
999 |
The solution $\phi _{nh}\ $to (\ref{eq:3d-invert}) and (\ref{homneuman}) |
The solution $\phi _{nh}\ $to (\ref{eq:3d-invert}) and (\ref{eq:inhom-neumann-nh}) |
1000 |
does not vanish at $r=R_{moving}$, and so refines the pressure there. |
does not vanish at $r=R_{moving}$, and so refines the pressure there. |
1001 |
|
|
1002 |
\subsection{Forcing/dissipation} |
\subsection{Forcing/dissipation} |
1004 |
\subsubsection{Forcing} |
\subsubsection{Forcing} |
1005 |
|
|
1006 |
The forcing terms $\mathcal{F}$ on the rhs of the equations are provided by |
The forcing terms $\mathcal{F}$ on the rhs of the equations are provided by |
1007 |
`physics packages' described in detail in chapter ??. |
`physics packages' and forcing packages. These are described later on. |
1008 |
|
|
1009 |
\subsubsection{Dissipation} |
\subsubsection{Dissipation} |
1010 |
|
|
1014 |
biharmonic frictions are commonly used: |
biharmonic frictions are commonly used: |
1015 |
|
|
1016 |
\begin{equation} |
\begin{equation} |
1017 |
D_{V}=A_{h}\nabla _{h}^{2}v+A_{v}\frac{\partial ^{2}v}{\partial z^{2}}% |
D_{V}=A_{h}\nabla _{h}^{2}v+A_{v}\frac{\partial ^{2}v}{\partial z^{2}} |
1018 |
+A_{4}\nabla _{h}^{4}v \label{eq:dissipation} |
+A_{4}\nabla _{h}^{4}v \label{eq:dissipation} |
1019 |
\end{equation} |
\end{equation} |
1020 |
where $A_{h}$ and $A_{v}\ $are (constant) horizontal and vertical viscosity |
where $A_{h}$ and $A_{v}\ $are (constant) horizontal and vertical viscosity |
1025 |
|
|
1026 |
The mixing terms for the temperature and salinity equations have a similar |
The mixing terms for the temperature and salinity equations have a similar |
1027 |
form to that of momentum except that the diffusion tensor can be |
form to that of momentum except that the diffusion tensor can be |
1028 |
non-diagonal and have varying coefficients. $\qquad $% |
non-diagonal and have varying coefficients. $\qquad $ |
1029 |
\begin{equation} |
\begin{equation} |
1030 |
D_{T,S}=\nabla .[\underline{\underline{K}}\nabla (T,S)]+K_{4}\nabla |
D_{T,S}=\nabla .[\underline{\underline{K}}\nabla (T,S)]+K_{4}\nabla |
1031 |
_{h}^{4}(T,S) \label{eq:diffusion} |
_{h}^{4}(T,S) \label{eq:diffusion} |
1032 |
\end{equation} |
\end{equation} |
1033 |
where $\underline{\underline{K}}\ $is the diffusion tensor and the $K_{4}\ $% |
where $\underline{\underline{K}}\ $is the diffusion tensor and the $K_{4}\ $ |
1034 |
horizontal coefficient for biharmonic diffusion. In the simplest case where |
horizontal coefficient for biharmonic diffusion. In the simplest case where |
1035 |
the subgrid-scale fluxes of heat and salt are parameterized with constant |
the subgrid-scale fluxes of heat and salt are parameterized with constant |
1036 |
horizontal and vertical diffusion coefficients, $\underline{\underline{K}}$, |
horizontal and vertical diffusion coefficients, $\underline{\underline{K}}$, |
1041 |
\begin{array}{ccc} |
\begin{array}{ccc} |
1042 |
K_{h} & 0 & 0 \\ |
K_{h} & 0 & 0 \\ |
1043 |
0 & K_{h} & 0 \\ |
0 & K_{h} & 0 \\ |
1044 |
0 & 0 & K_{v}% |
0 & 0 & K_{v} |
1045 |
\end{array} |
\end{array} |
1046 |
\right) \qquad \qquad \qquad \label{eq:diagonal-diffusion-tensor} |
\right) \qquad \qquad \qquad \label{eq:diagonal-diffusion-tensor} |
1047 |
\end{equation} |
\end{equation} |
1051 |
|
|
1052 |
\subsection{Vector invariant form} |
\subsection{Vector invariant form} |
1053 |
|
|
1054 |
For some purposes it is advantageous to write momentum advection in eq(\ref% |
For some purposes it is advantageous to write momentum advection in eq(\ref |
1055 |
{hor-mtm}) and (\ref{vertmtm}) in the (so-called) `vector invariant' form: |
{eq:horizontal_mtm}) and (\ref{eq:vertical_mtm}) in the (so-called) `vector invariant' form: |
1056 |
|
|
1057 |
\begin{equation} |
\begin{equation} |
1058 |
\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} |
1059 |
+\left( \nabla \times \vec{\mathbf{v}}\right) \times \vec{\mathbf{v}}+\nabla % |
+\left( \nabla \times \vec{\mathbf{v}}\right) \times \vec{\mathbf{v}}+\nabla |
1060 |
\left[ \frac{1}{2}(\vec{\mathbf{v}}\cdot \vec{\mathbf{v}})\right] |
\left[ \frac{1}{2}(\vec{\mathbf{v}}\cdot \vec{\mathbf{v}})\right] |
1061 |
\label{eq:vi-identity} |
\label{eq:vi-identity} |
1062 |
\end{equation}% |
\end{equation} |
1063 |
This permits alternative numerical treatments of the non-linear terms based |
This permits alternative numerical treatments of the non-linear terms based |
1064 |
on their representation as a vorticity flux. Because gradients of coordinate |
on their representation as a vorticity flux. Because gradients of coordinate |
1065 |
vectors no longer appear on the rhs of (\ref{eq:vi-identity}), explicit |
vectors no longer appear on the rhs of (\ref{eq:vi-identity}), explicit |
1066 |
representation of the metric terms in (\ref{eq:gu-speherical}), (\ref% |
representation of the metric terms in (\ref{eq:gu-speherical}), (\ref |
1067 |
{eq:gv-spherical}) and (\ref{eq:gw-spherical}), can be avoided: information |
{eq:gv-spherical}) and (\ref{eq:gw-spherical}), can be avoided: information |
1068 |
about the geometry is contained in the areas and lengths of the volumes used |
about the geometry is contained in the areas and lengths of the volumes used |
1069 |
to discretize the model. |
to discretize the model. |
1070 |
|
|
1071 |
\subsection{Adjoint} |
\subsection{Adjoint} |
1072 |
|
|
1073 |
Tangent linear and adjoint counterparts of the forward model and described |
Tangent linear and adjoint counterparts of the forward model are described |
1074 |
in Chapter 5. |
in Chapter 5. |
1075 |
|
|
1076 |
% $Header$ |
% $Header$ |
1085 |
|
|
1086 |
The hydrostatic primitive equations (HPEs) in p-coordinates are: |
The hydrostatic primitive equations (HPEs) in p-coordinates are: |
1087 |
\begin{eqnarray} |
\begin{eqnarray} |
1088 |
\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}} |
1089 |
_{h}+\mathbf{\nabla }_{p}\phi &=&\vec{\mathbf{\mathcal{F}}} |
_{h}+\mathbf{\nabla }_{p}\phi &=&\vec{\mathbf{\mathcal{F}}} |
1090 |
\label{eq:atmos-mom} \\ |
\label{eq:atmos-mom} \\ |
1091 |
\frac{\partial \phi }{\partial p}+\alpha &=&0 \label{eq-p-hydro-start} \\ |
\frac{\partial \phi }{\partial p}+\alpha &=&0 \label{eq-p-hydro-start} \\ |
1092 |
\mathbf{\nabla }_{p}\cdot \vec{\mathbf{v}}_{h}+\frac{\partial \omega }{% |
\mathbf{\nabla }_{p}\cdot \vec{\mathbf{v}}_{h}+\frac{\partial \omega }{ |
1093 |
\partial p} &=&0 \label{eq:atmos-cont} \\ |
\partial p} &=&0 \label{eq:atmos-cont} \\ |
1094 |
p\alpha &=&RT \label{eq:atmos-eos} \\ |
p\alpha &=&RT \label{eq:atmos-eos} \\ |
1095 |
c_{v}\frac{DT}{Dt}+p\frac{D\alpha }{Dt} &=&\mathcal{Q} \label{eq:atmos-heat} |
c_{v}\frac{DT}{Dt}+p\frac{D\alpha }{Dt} &=&\mathcal{Q} \label{eq:atmos-heat} |
1096 |
\end{eqnarray}% |
\end{eqnarray} |
1097 |
where $\vec{\mathbf{v}}_{h}=(u,v,0)$ is the `horizontal' (on pressure |
where $\vec{\mathbf{v}}_{h}=(u,v,0)$ is the `horizontal' (on pressure |
1098 |
surfaces) component of velocity,$\frac{D}{Dt}=\vec{\mathbf{v}}_{h}\cdot |
surfaces) component of velocity,$\frac{D}{Dt}=\vec{\mathbf{v}}_{h}\cdot |
1099 |
\mathbf{\nabla }_{p}+\omega \frac{\partial }{\partial p}$ is the total |
\mathbf{\nabla }_{p}+\omega \frac{\partial }{\partial p}$ is the total |
1100 |
derivative, $f=2\Omega \sin lat$ is the Coriolis parameter, $\phi =gz$ is |
derivative, $f=2\Omega \sin \varphi$ is the Coriolis parameter, $\phi =gz$ is |
1101 |
the geopotential, $\alpha =1/\rho $ is the specific volume, $\omega =\frac{Dp% |
the geopotential, $\alpha =1/\rho $ is the specific volume, $\omega =\frac{Dp |
1102 |
}{Dt}$ is the vertical velocity in the $p-$coordinate. Equation(\ref% |
}{Dt}$ is the vertical velocity in the $p-$coordinate. Equation(\ref |
1103 |
{eq:atmos-heat}) is the first law of thermodynamics where internal energy $% |
{eq:atmos-heat}) is the first law of thermodynamics where internal energy $ |
1104 |
e=c_{v}T$, $T$ is temperature, $Q$ is the rate of heating per unit mass and $% |
e=c_{v}T$, $T$ is temperature, $Q$ is the rate of heating per unit mass and $ |
1105 |
p\frac{D\alpha }{Dt}$ is the work done by the fluid in compressing. |
p\frac{D\alpha }{Dt}$ is the work done by the fluid in compressing. |
1106 |
|
|
1107 |
It is convenient to cast the heat equation in terms of potential temperature |
It is convenient to cast the heat equation in terms of potential temperature |
1109 |
Differentiating (\ref{eq:atmos-eos}) we get: |
Differentiating (\ref{eq:atmos-eos}) we get: |
1110 |
\begin{equation*} |
\begin{equation*} |
1111 |
p\frac{D\alpha }{Dt}+\alpha \frac{Dp}{Dt}=R\frac{DT}{Dt} |
p\frac{D\alpha }{Dt}+\alpha \frac{Dp}{Dt}=R\frac{DT}{Dt} |
1112 |
\end{equation*}% |
\end{equation*} |
1113 |
which, when added to the heat equation (\ref{eq:atmos-heat}) and using $% |
which, when added to the heat equation (\ref{eq:atmos-heat}) and using $ |
1114 |
c_{p}=c_{v}+R$, gives: |
c_{p}=c_{v}+R$, gives: |
1115 |
\begin{equation} |
\begin{equation} |
1116 |
c_{p}\frac{DT}{Dt}-\alpha \frac{Dp}{Dt}=\mathcal{Q} |
c_{p}\frac{DT}{Dt}-\alpha \frac{Dp}{Dt}=\mathcal{Q} |
1117 |
\label{eq-p-heat-interim} |
\label{eq-p-heat-interim} |
1118 |
\end{equation}% |
\end{equation} |
1119 |
Potential temperature is defined: |
Potential temperature is defined: |
1120 |
\begin{equation} |
\begin{equation} |
1121 |
\theta =T(\frac{p_{c}}{p})^{\kappa } \label{eq:potential-temp} |
\theta =T(\frac{p_{c}}{p})^{\kappa } \label{eq:potential-temp} |
1122 |
\end{equation}% |
\end{equation} |
1123 |
where $p_{c}$ is a reference pressure and $\kappa =R/c_{p}$. For convenience |
where $p_{c}$ is a reference pressure and $\kappa =R/c_{p}$. For convenience |
1124 |
we will make use of the Exner function $\Pi (p)$ which defined by: |
we will make use of the Exner function $\Pi (p)$ which defined by: |
1125 |
\begin{equation} |
\begin{equation} |
1126 |
\Pi (p)=c_{p}(\frac{p}{p_{c}})^{\kappa } \label{Exner} |
\Pi (p)=c_{p}(\frac{p}{p_{c}})^{\kappa } \label{Exner} |
1127 |
\end{equation}% |
\end{equation} |
1128 |
The following relations will be useful and are easily expressed in terms of |
The following relations will be useful and are easily expressed in terms of |
1129 |
the Exner function: |
the Exner function: |
1130 |
\begin{equation*} |
\begin{equation*} |
1131 |
c_{p}T=\Pi \theta \;\;;\;\;\frac{\partial \Pi }{\partial p}=\frac{\kappa \Pi |
c_{p}T=\Pi \theta \;\;;\;\;\frac{\partial \Pi }{\partial p}=\frac{\kappa \Pi |
1132 |
}{p}\;\;;\;\;\alpha =\frac{\kappa \Pi \theta }{p}=\frac{\partial \ \Pi }{% |
}{p}\;\;;\;\;\alpha =\frac{\kappa \Pi \theta }{p}=\frac{\partial \ \Pi }{ |
1133 |
\partial p}\theta \;\;;\;\;\frac{D\Pi }{Dt}=\frac{\partial \Pi }{\partial p}% |
\partial p}\theta \;\;;\;\;\frac{D\Pi }{Dt}=\frac{\partial \Pi }{\partial p} |
1134 |
\frac{Dp}{Dt} |
\frac{Dp}{Dt} |
1135 |
\end{equation*}% |
\end{equation*} |
1136 |
where $b=\frac{\partial \ \Pi }{\partial p}\theta $ is the buoyancy. |
where $b=\frac{\partial \ \Pi }{\partial p}\theta $ is the buoyancy. |
1137 |
|
|
1138 |
The heat equation is obtained by noting that |
The heat equation is obtained by noting that |
1147 |
\end{equation} |
\end{equation} |
1148 |
which is in conservative form. |
which is in conservative form. |
1149 |
|
|
1150 |
For convenience in the model we prefer to step forward (\ref% |
For convenience in the model we prefer to step forward (\ref |
1151 |
{eq:potential-temperature-equation}) rather than (\ref{eq:atmos-heat}). |
{eq:potential-temperature-equation}) rather than (\ref{eq:atmos-heat}). |
1152 |
|
|
1153 |
\subsubsection{Boundary conditions} |
\subsubsection{Boundary conditions} |
1191 |
|
|
1192 |
The final form of the HPE's in p coordinates is then: |
The final form of the HPE's in p coordinates is then: |
1193 |
\begin{eqnarray} |
\begin{eqnarray} |
1194 |
\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}} |
1195 |
_{h}+\mathbf{\nabla }_{p}\phi ^{\prime } &=&\vec{\mathbf{\mathcal{F}}} \\ |
_{h}+\mathbf{\nabla }_{p}\phi ^{\prime } &=&\vec{\mathbf{\mathcal{F}}} \label{eq:atmos-prime} \\ |
1196 |
\frac{\partial \phi ^{\prime }}{\partial p}+\alpha ^{\prime } &=&0 \\ |
\frac{\partial \phi ^{\prime }}{\partial p}+\alpha ^{\prime } &=&0 \\ |
1197 |
\mathbf{\nabla }_{p}\cdot \vec{\mathbf{v}}_{h}+\frac{\partial \omega }{% |
\mathbf{\nabla }_{p}\cdot \vec{\mathbf{v}}_{h}+\frac{\partial \omega }{ |
1198 |
\partial p} &=&0 \\ |
\partial p} &=&0 \\ |
1199 |
\frac{\partial \Pi }{\partial p}\theta ^{\prime } &=&\alpha ^{\prime } \\ |
\frac{\partial \Pi }{\partial p}\theta ^{\prime } &=&\alpha ^{\prime } \\ |
1200 |
\frac{D\theta }{Dt} &=&\frac{\mathcal{Q}}{\Pi } \label{eq:atmos-prime} |
\frac{D\theta }{Dt} &=&\frac{\mathcal{Q}}{\Pi } |
1201 |
\end{eqnarray} |
\end{eqnarray} |
1202 |
|
|
1203 |
% $Header$ |
% $Header$ |
1211 |
HPE's for the ocean written in z-coordinates are obtained. The |
HPE's for the ocean written in z-coordinates are obtained. The |
1212 |
non-Boussinesq equations for oceanic motion are: |
non-Boussinesq equations for oceanic motion are: |
1213 |
\begin{eqnarray} |
\begin{eqnarray} |
1214 |
\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}} |
1215 |
_{h}+\frac{1}{\rho }\mathbf{\nabla }_{z}p &=&\vec{\mathbf{\mathcal{F}}} \\ |
_{h}+\frac{1}{\rho }\mathbf{\nabla }_{z}p &=&\vec{\mathbf{\mathcal{F}}} \\ |
1216 |
\epsilon _{nh}\frac{Dw}{Dt}+g+\frac{1}{\rho }\frac{\partial p}{\partial z} |
\epsilon _{nh}\frac{Dw}{Dt}+g+\frac{1}{\rho }\frac{\partial p}{\partial z} |
1217 |
&=&\epsilon _{nh}\mathcal{F}_{w} \\ |
&=&\epsilon _{nh}\mathcal{F}_{w} \\ |
1218 |
\frac{1}{\rho }\frac{D\rho }{Dt}+\mathbf{\nabla }_{z}\cdot \vec{\mathbf{v}}% |
\frac{1}{\rho }\frac{D\rho }{Dt}+\mathbf{\nabla }_{z}\cdot \vec{\mathbf{v}} |
1219 |
_{h}+\frac{\partial w}{\partial z} &=&0 \\ |
_{h}+\frac{\partial w}{\partial z} &=&0 \label{eq-zns-cont}\\ |
1220 |
\rho &=&\rho (\theta ,S,p) \\ |
\rho &=&\rho (\theta ,S,p) \label{eq-zns-eos}\\ |
1221 |
\frac{D\theta }{Dt} &=&\mathcal{Q}_{\theta } \\ |
\frac{D\theta }{Dt} &=&\mathcal{Q}_{\theta } \label{eq-zns-heat}\\ |
1222 |
\frac{DS}{Dt} &=&\mathcal{Q}_{s} \label{eq:non-boussinesq} |
\frac{DS}{Dt} &=&\mathcal{Q}_{s} \label{eq-zns-salt} |
1223 |
\end{eqnarray}% |
\label{eq:non-boussinesq} |
1224 |
|
\end{eqnarray} |
1225 |
These equations permit acoustics modes, inertia-gravity waves, |
These equations permit acoustics modes, inertia-gravity waves, |
1226 |
non-hydrostatic motions, a geostrophic (Rossby) mode and a thermo-haline |
non-hydrostatic motions, a geostrophic (Rossby) mode and a thermohaline |
1227 |
mode. As written, they cannot be integrated forward consistently - if we |
mode. As written, they cannot be integrated forward consistently - if we |
1228 |
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 |
1229 |
consistent with that obtained by stepping (\ref{eq-zns-heat}) and (\ref% |
consistent with that obtained by stepping (\ref{eq-zns-heat}) and (\ref |
1230 |
{eq-zns-salt}) and then using (\ref{eq-zns-eos}) to yield $\rho $. It is |
{eq-zns-salt}) and then using (\ref{eq-zns-eos}) to yield $\rho $. It is |
1231 |
therefore necessary to manipulate the system as follows. Differentiating the |
therefore necessary to manipulate the system as follows. Differentiating the |
1232 |
EOS (equation of state) gives: |
EOS (equation of state) gives: |
1239 |
\end{equation} |
\end{equation} |
1240 |
|
|
1241 |
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 the |
1242 |
reciprocal of the sound speed ($c_{s}$) squared. Substituting into \ref% |
reciprocal of the sound speed ($c_{s}$) squared. Substituting into \ref{eq-zns-cont} gives: |
|
{eq-zns-cont} gives: |
|
1243 |
\begin{equation} |
\begin{equation} |
1244 |
\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{ |
1245 |
v}}+\partial _{z}w\approx 0 \label{eq-zns-pressure} |
v}}+\partial _{z}w\approx 0 \label{eq-zns-pressure} |
1246 |
\end{equation} |
\end{equation} |
1247 |
where we have used an approximation sign to indicate that we have assumed |
where we have used an approximation sign to indicate that we have assumed |
1249 |
Replacing \ref{eq-zns-cont} with \ref{eq-zns-pressure} yields a system that |
Replacing \ref{eq-zns-cont} with \ref{eq-zns-pressure} yields a system that |
1250 |
can be explicitly integrated forward: |
can be explicitly integrated forward: |
1251 |
\begin{eqnarray} |
\begin{eqnarray} |
1252 |
\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}} |
1253 |
_{h}+\frac{1}{\rho }\mathbf{\nabla }_{z}p &=&\vec{\mathbf{\mathcal{F}}} |
_{h}+\frac{1}{\rho }\mathbf{\nabla }_{z}p &=&\vec{\mathbf{\mathcal{F}}} |
1254 |
\label{eq-cns-hmom} \\ |
\label{eq-cns-hmom} \\ |
1255 |
\epsilon _{nh}\frac{Dw}{Dt}+g+\frac{1}{\rho }\frac{\partial p}{\partial z} |
\epsilon _{nh}\frac{Dw}{Dt}+g+\frac{1}{\rho }\frac{\partial p}{\partial z} |
1256 |
&=&\epsilon _{nh}\mathcal{F}_{w} \label{eq-cns-hydro} \\ |
&=&\epsilon _{nh}\mathcal{F}_{w} \label{eq-cns-hydro} \\ |
1257 |
\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{ |
1258 |
v}}_{h}+\frac{\partial w}{\partial z} &=&0 \label{eq-cns-cont} \\ |
v}}_{h}+\frac{\partial w}{\partial z} &=&0 \label{eq-cns-cont} \\ |
1259 |
\rho &=&\rho (\theta ,S,p) \label{eq-cns-eos} \\ |
\rho &=&\rho (\theta ,S,p) \label{eq-cns-eos} \\ |
1260 |
\frac{D\theta }{Dt} &=&\mathcal{Q}_{\theta } \label{eq-cns-heat} \\ |
\frac{D\theta }{Dt} &=&\mathcal{Q}_{\theta } \label{eq-cns-heat} \\ |
1268 |
`Boussinesq assumption'. The only term that then retains the full variation |
`Boussinesq assumption'. The only term that then retains the full variation |
1269 |
in $\rho $ is the gravitational acceleration: |
in $\rho $ is the gravitational acceleration: |
1270 |
\begin{eqnarray} |
\begin{eqnarray} |
1271 |
\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}} |
1272 |
_{h}+\frac{1}{\rho _{o}}\mathbf{\nabla }_{z}p &=&\vec{\mathbf{\mathcal{F}}} |
_{h}+\frac{1}{\rho _{o}}\mathbf{\nabla }_{z}p &=&\vec{\mathbf{\mathcal{F}}} |
1273 |
\label{eq-zcb-hmom} \\ |
\label{eq-zcb-hmom} \\ |
1274 |
\epsilon _{nh}\frac{Dw}{Dt}+\frac{g\rho }{\rho _{o}}+\frac{1}{\rho _{o}}% |
\epsilon _{nh}\frac{Dw}{Dt}+\frac{g\rho }{\rho _{o}}+\frac{1}{\rho _{o}} |
1275 |
\frac{\partial p}{\partial z} &=&\epsilon _{nh}\mathcal{F}_{w} |
\frac{\partial p}{\partial z} &=&\epsilon _{nh}\mathcal{F}_{w} |
1276 |
\label{eq-zcb-hydro} \\ |
\label{eq-zcb-hydro} \\ |
1277 |
\frac{1}{\rho _{o}c_{s}^{2}}\frac{Dp}{Dt}+\mathbf{\nabla }_{z}\cdot \vec{% |
\frac{1}{\rho _{o}c_{s}^{2}}\frac{Dp}{Dt}+\mathbf{\nabla }_{z}\cdot \vec{ |
1278 |
\mathbf{v}}_{h}+\frac{\partial w}{\partial z} &=&0 \label{eq-zcb-cont} \\ |
\mathbf{v}}_{h}+\frac{\partial w}{\partial z} &=&0 \label{eq-zcb-cont} \\ |
1279 |
\rho &=&\rho (\theta ,S,p) \label{eq-zcb-eos} \\ |
\rho &=&\rho (\theta ,S,p) \label{eq-zcb-eos} \\ |
1280 |
\frac{D\theta }{Dt} &=&\mathcal{Q}_{\theta } \label{eq-zcb-heat} \\ |
\frac{D\theta }{Dt} &=&\mathcal{Q}_{\theta } \label{eq-zcb-heat} \\ |
1281 |
\frac{DS}{Dt} &=&\mathcal{Q}_{s} \label{eq-zcb-salt} |
\frac{DS}{Dt} &=&\mathcal{Q}_{s} \label{eq-zcb-salt} |
1282 |
\end{eqnarray} |
\end{eqnarray} |
1283 |
These equations still retain acoustic modes. But, because the |
These equations still retain acoustic modes. But, because the |
1284 |
``compressible'' terms are linearized, the pressure equation \ref% |
``compressible'' terms are linearized, the pressure equation \ref |
1285 |
{eq-zcb-cont} can be integrated implicitly with ease (the time-dependent |
{eq-zcb-cont} can be integrated implicitly with ease (the time-dependent |
1286 |
term appears as a Helmholtz term in the non-hydrostatic pressure equation). |
term appears as a Helmholtz term in the non-hydrostatic pressure equation). |
1287 |
These are the \emph{truly} compressible Boussinesq equations. Note that the |
These are the \emph{truly} compressible Boussinesq equations. Note that the |
1288 |
EOS must have the same pressure dependency as the linearized pressure term, |
EOS must have the same pressure dependency as the linearized pressure term, |
1289 |
ie. $\left. \frac{\partial \rho }{\partial p}\right| _{\theta ,S}=\frac{1}{% |
ie. $\left. \frac{\partial \rho }{\partial p}\right| _{\theta ,S}=\frac{1}{ |
1290 |
c_{s}^{2}}$, for consistency. |
c_{s}^{2}}$, for consistency. |
1291 |
|
|
1292 |
\subsubsection{`Anelastic' z-coordinate equations} |
\subsubsection{`Anelastic' z-coordinate equations} |
1293 |
|
|
1294 |
The anelastic approximation filters the acoustic mode by removing the |
The anelastic approximation filters the acoustic mode by removing the |
1295 |
time-dependency in the continuity (now pressure-) equation (\ref{eq-zcb-cont}% |
time-dependency in the continuity (now pressure-) equation (\ref{eq-zcb-cont} |
1296 |
). This could be done simply by noting that $\frac{Dp}{Dt}\approx -g\rho _{o}% |
). This could be done simply by noting that $\frac{Dp}{Dt}\approx -g\rho _{o} |
1297 |
\frac{Dz}{Dt}=-g\rho _{o}w$, but this leads to an inconsistency between |
\frac{Dz}{Dt}=-g\rho _{o}w$, but this leads to an inconsistency between |
1298 |
continuity and EOS. A better solution is to change the dependency on |
continuity and EOS. A better solution is to change the dependency on |
1299 |
pressure in the EOS by splitting the pressure into a reference function of |
pressure in the EOS by splitting the pressure into a reference function of |
1304 |
Remembering that the term $\frac{Dp}{Dt}$ in continuity comes from |
Remembering that the term $\frac{Dp}{Dt}$ in continuity comes from |
1305 |
differentiating the EOS, the continuity equation then becomes: |
differentiating the EOS, the continuity equation then becomes: |
1306 |
\begin{equation*} |
\begin{equation*} |
1307 |
\frac{1}{\rho _{o}c_{s}^{2}}\left( \frac{Dp_{o}}{Dt}+\epsilon _{s}\frac{% |
\frac{1}{\rho _{o}c_{s}^{2}}\left( \frac{Dp_{o}}{Dt}+\epsilon _{s}\frac{ |
1308 |
Dp^{\prime }}{Dt}\right) +\mathbf{\nabla }_{z}\cdot \vec{\mathbf{v}}_{h}+% |
Dp^{\prime }}{Dt}\right) +\mathbf{\nabla }_{z}\cdot \vec{\mathbf{v}}_{h}+ |
1309 |
\frac{\partial w}{\partial z}=0 |
\frac{\partial w}{\partial z}=0 |
1310 |
\end{equation*} |
\end{equation*} |
1311 |
If the time- and space-scales of the motions of interest are longer than |
If the time- and space-scales of the motions of interest are longer than |
1312 |
those of acoustic modes, then $\frac{Dp^{\prime }}{Dt}<<(\frac{Dp_{o}}{Dt},% |
those of acoustic modes, then $\frac{Dp^{\prime }}{Dt}<<(\frac{Dp_{o}}{Dt}, |
1313 |
\mathbf{\nabla }\cdot \vec{\mathbf{v}}_{h})$ in the continuity equations and |
\mathbf{\nabla }\cdot \vec{\mathbf{v}}_{h})$ in the continuity equations and |
1314 |
$\left. \frac{\partial \rho }{\partial p}\right| _{\theta ,S}\frac{% |
$\left. \frac{\partial \rho }{\partial p}\right| _{\theta ,S}\frac{ |
1315 |
Dp^{\prime }}{Dt}<<\left. \frac{\partial \rho }{\partial p}\right| _{\theta |
Dp^{\prime }}{Dt}<<\left. \frac{\partial \rho }{\partial p}\right| _{\theta |
1316 |
,S}\frac{Dp_{o}}{Dt}$ in the EOS (\ref{EOSexpansion}). Thus we set $\epsilon |
,S}\frac{Dp_{o}}{Dt}$ in the EOS (\ref{EOSexpansion}). Thus we set $\epsilon |
1317 |
_{s}=0$, removing the dependency on $p^{\prime }$ in the continuity equation |
_{s}=0$, removing the dependency on $p^{\prime }$ in the continuity equation |
1318 |
and EOS. Expanding $\frac{Dp_{o}(z)}{Dt}=-g\rho _{o}w$ then leads to the |
and EOS. Expanding $\frac{Dp_{o}(z)}{Dt}=-g\rho _{o}w$ then leads to the |
1319 |
anelastic continuity equation: |
anelastic continuity equation: |
1320 |
\begin{equation} |
\begin{equation} |
1321 |
\mathbf{\nabla }_{z}\cdot \vec{\mathbf{v}}_{h}+\frac{\partial w}{\partial z}-% |
\mathbf{\nabla }_{z}\cdot \vec{\mathbf{v}}_{h}+\frac{\partial w}{\partial z}- |
1322 |
\frac{g}{c_{s}^{2}}w=0 \label{eq-za-cont1} |
\frac{g}{c_{s}^{2}}w=0 \label{eq-za-cont1} |
1323 |
\end{equation} |
\end{equation} |
1324 |
A slightly different route leads to the quasi-Boussinesq continuity equation |
A slightly different route leads to the quasi-Boussinesq continuity equation |
1325 |
where we use the scaling $\frac{\partial \rho ^{\prime }}{\partial t}+% |
where we use the scaling $\frac{\partial \rho ^{\prime }}{\partial t}+ |
1326 |
\mathbf{\nabla }_{3}\cdot \rho ^{\prime }\vec{\mathbf{v}}<<\mathbf{\nabla }% |
\mathbf{\nabla }_{3}\cdot \rho ^{\prime }\vec{\mathbf{v}}<<\mathbf{\nabla } |
1327 |
_{3}\cdot \rho _{o}\vec{\mathbf{v}}$ yielding: |
_{3}\cdot \rho _{o}\vec{\mathbf{v}}$ yielding: |
1328 |
\begin{equation} |
\begin{equation} |
1329 |
\mathbf{\nabla }_{z}\cdot \vec{\mathbf{v}}_{h}+\frac{1}{\rho _{o}}\frac{% |
\mathbf{\nabla }_{z}\cdot \vec{\mathbf{v}}_{h}+\frac{1}{\rho _{o}}\frac{ |
1330 |
\partial \left( \rho _{o}w\right) }{\partial z}=0 \label{eq-za-cont2} |
\partial \left( \rho _{o}w\right) }{\partial z}=0 \label{eq-za-cont2} |
1331 |
\end{equation} |
\end{equation} |
1332 |
Equations \ref{eq-za-cont1} and \ref{eq-za-cont2} are in fact the same |
Equations \ref{eq-za-cont1} and \ref{eq-za-cont2} are in fact the same |
1335 |
\frac{1}{\rho _{o}}\frac{\partial \rho _{o}}{\partial z}=\frac{-g}{c_{s}^{2}} |
\frac{1}{\rho _{o}}\frac{\partial \rho _{o}}{\partial z}=\frac{-g}{c_{s}^{2}} |
1336 |
\end{equation} |
\end{equation} |
1337 |
Again, note that if $\rho _{o}$ is evaluated from prescribed $\theta _{o}$ |
Again, note that if $\rho _{o}$ is evaluated from prescribed $\theta _{o}$ |
1338 |
and $S_{o}$ profiles, then the EOS dependency on $p_{o}$ and the term $\frac{% |
and $S_{o}$ profiles, then the EOS dependency on $p_{o}$ and the term $\frac{ |
1339 |
g}{c_{s}^{2}}$ in continuity should be referred to those same profiles. The |
g}{c_{s}^{2}}$ in continuity should be referred to those same profiles. The |
1340 |
full set of `quasi-Boussinesq' or `anelastic' equations for the ocean are |
full set of `quasi-Boussinesq' or `anelastic' equations for the ocean are |
1341 |
then: |
then: |
1342 |
\begin{eqnarray} |
\begin{eqnarray} |
1343 |
\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}} |
1344 |
_{h}+\frac{1}{\rho _{o}}\mathbf{\nabla }_{z}p &=&\vec{\mathbf{\mathcal{F}}} |
_{h}+\frac{1}{\rho _{o}}\mathbf{\nabla }_{z}p &=&\vec{\mathbf{\mathcal{F}}} |
1345 |
\label{eq-zab-hmom} \\ |
\label{eq-zab-hmom} \\ |
1346 |
\epsilon _{nh}\frac{Dw}{Dt}+\frac{g\rho }{\rho _{o}}+\frac{1}{\rho _{o}}% |
\epsilon _{nh}\frac{Dw}{Dt}+\frac{g\rho }{\rho _{o}}+\frac{1}{\rho _{o}} |
1347 |
\frac{\partial p}{\partial z} &=&\epsilon _{nh}\mathcal{F}_{w} |
\frac{\partial p}{\partial z} &=&\epsilon _{nh}\mathcal{F}_{w} |
1348 |
\label{eq-zab-hydro} \\ |
\label{eq-zab-hydro} \\ |
1349 |
\mathbf{\nabla }_{z}\cdot \vec{\mathbf{v}}_{h}+\frac{1}{\rho _{o}}\frac{% |
\mathbf{\nabla }_{z}\cdot \vec{\mathbf{v}}_{h}+\frac{1}{\rho _{o}}\frac{ |
1350 |
\partial \left( \rho _{o}w\right) }{\partial z} &=&0 \label{eq-zab-cont} \\ |
\partial \left( \rho _{o}w\right) }{\partial z} &=&0 \label{eq-zab-cont} \\ |
1351 |
\rho &=&\rho (\theta ,S,p_{o}(z)) \label{eq-zab-eos} \\ |
\rho &=&\rho (\theta ,S,p_{o}(z)) \label{eq-zab-eos} \\ |
1352 |
\frac{D\theta }{Dt} &=&\mathcal{Q}_{\theta } \label{eq-zab-heat} \\ |
\frac{D\theta }{Dt} &=&\mathcal{Q}_{\theta } \label{eq-zab-heat} \\ |
1359 |
technically, to also remove the dependence of $\rho $ on $p_{o}$. This would |
technically, to also remove the dependence of $\rho $ on $p_{o}$. This would |
1360 |
yield the ``truly'' incompressible Boussinesq equations: |
yield the ``truly'' incompressible Boussinesq equations: |
1361 |
\begin{eqnarray} |
\begin{eqnarray} |
1362 |
\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}} |
1363 |
_{h}+\frac{1}{\rho _{c}}\mathbf{\nabla }_{z}p &=&\vec{\mathbf{\mathcal{F}}} |
_{h}+\frac{1}{\rho _{c}}\mathbf{\nabla }_{z}p &=&\vec{\mathbf{\mathcal{F}}} |
1364 |
\label{eq-ztb-hmom} \\ |
\label{eq-ztb-hmom} \\ |
1365 |
\epsilon _{nh}\frac{Dw}{Dt}+\frac{g\rho }{\rho _{c}}+\frac{1}{\rho _{c}}% |
\epsilon _{nh}\frac{Dw}{Dt}+\frac{g\rho }{\rho _{c}}+\frac{1}{\rho _{c}} |
1366 |
\frac{\partial p}{\partial z} &=&\epsilon _{nh}\mathcal{F}_{w} |
\frac{\partial p}{\partial z} &=&\epsilon _{nh}\mathcal{F}_{w} |
1367 |
\label{eq-ztb-hydro} \\ |
\label{eq-ztb-hydro} \\ |
1368 |
\mathbf{\nabla }_{z}\cdot \vec{\mathbf{v}}_{h}+\frac{\partial w}{\partial z} |
\mathbf{\nabla }_{z}\cdot \vec{\mathbf{v}}_{h}+\frac{\partial w}{\partial z} |
1381 |
density thus: |
density thus: |
1382 |
\begin{equation*} |
\begin{equation*} |
1383 |
\rho =\rho _{o}+\rho ^{\prime } |
\rho =\rho _{o}+\rho ^{\prime } |
1384 |
\end{equation*}% |
\end{equation*} |
1385 |
We then assert that variations with depth of $\rho _{o}$ are unimportant |
We then assert that variations with depth of $\rho _{o}$ are unimportant |
1386 |
while the compressible effects in $\rho ^{\prime }$ are: |
while the compressible effects in $\rho ^{\prime }$ are: |
1387 |
\begin{equation*} |
\begin{equation*} |
1388 |
\rho _{o}=\rho _{c} |
\rho _{o}=\rho _{c} |
1389 |
\end{equation*}% |
\end{equation*} |
1390 |
\begin{equation*} |
\begin{equation*} |
1391 |
\rho ^{\prime }=\rho (\theta ,S,p_{o}(z))-\rho _{o} |
\rho ^{\prime }=\rho (\theta ,S,p_{o}(z))-\rho _{o} |
1392 |
\end{equation*}% |
\end{equation*} |
1393 |
This then yields what we can call the semi-compressible Boussinesq |
This then yields what we can call the semi-compressible Boussinesq |
1394 |
equations: |
equations: |
1395 |
\begin{eqnarray} |
\begin{eqnarray} |
1396 |
\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}} |
1397 |
_{h}+\frac{1}{\rho _{c}}\mathbf{\nabla }_{z}p^{\prime } &=&\vec{\mathbf{% |
_{h}+\frac{1}{\rho _{c}}\mathbf{\nabla }_{z}p^{\prime } &=&\vec{\mathbf{ |
1398 |
\mathcal{F}}} \label{eq:ocean-mom} \\ |
\mathcal{F}}} \label{eq:ocean-mom} \\ |
1399 |
\epsilon _{nh}\frac{Dw}{Dt}+\frac{g\rho ^{\prime }}{\rho _{c}}+\frac{1}{\rho |
\epsilon _{nh}\frac{Dw}{Dt}+\frac{g\rho ^{\prime }}{\rho _{c}}+\frac{1}{\rho |
1400 |
_{c}}\frac{\partial p^{\prime }}{\partial z} &=&\epsilon _{nh}\mathcal{F}_{w} |
_{c}}\frac{\partial p^{\prime }}{\partial z} &=&\epsilon _{nh}\mathcal{F}_{w} |
1405 |
\\ |
\\ |
1406 |
\frac{D\theta }{Dt} &=&\mathcal{Q}_{\theta } \label{eq:ocean-theta} \\ |
\frac{D\theta }{Dt} &=&\mathcal{Q}_{\theta } \label{eq:ocean-theta} \\ |
1407 |
\frac{DS}{Dt} &=&\mathcal{Q}_{s} \label{eq:ocean-salt} |
\frac{DS}{Dt} &=&\mathcal{Q}_{s} \label{eq:ocean-salt} |
1408 |
\end{eqnarray}% |
\end{eqnarray} |
1409 |
Note that the hydrostatic pressure of the resting fluid, including that |
Note that the hydrostatic pressure of the resting fluid, including that |
1410 |
associated with $\rho _{c}$, is subtracted out since it has no effect on the |
associated with $\rho _{c}$, is subtracted out since it has no effect on the |
1411 |
dynamics. |
dynamics. |
1429 |
and vertical direction respectively, are given by (see Fig.2) : |
and vertical direction respectively, are given by (see Fig.2) : |
1430 |
|
|
1431 |
\begin{equation*} |
\begin{equation*} |
1432 |
u=r\cos \phi \frac{D\lambda }{Dt} |
u=r\cos \varphi \frac{D\lambda }{Dt} |
1433 |
\end{equation*} |
\end{equation*} |
1434 |
|
|
1435 |
\begin{equation*} |
\begin{equation*} |
1436 |
v=r\frac{D\phi }{Dt}\qquad |
v=r\frac{D\varphi }{Dt}\qquad |
1437 |
\end{equation*} |
\end{equation*} |
1438 |
$\qquad \qquad \qquad \qquad $ |
$\qquad \qquad \qquad \qquad $ |
1439 |
|
|
1441 |
\dot{r}=\frac{Dr}{Dt} |
\dot{r}=\frac{Dr}{Dt} |
1442 |
\end{equation*} |
\end{equation*} |
1443 |
|
|
1444 |
Here $\phi $ is the latitude, $\lambda $ the longitude, $r$ the radial |
Here $\varphi $ is the latitude, $\lambda $ the longitude, $r$ the radial |
1445 |
distance of the particle from the center of the earth, $\Omega $ is the |
distance of the particle from the center of the earth, $\Omega $ is the |
1446 |
angular speed of rotation of the Earth and $D/Dt$ is the total derivative. |
angular speed of rotation of the Earth and $D/Dt$ is the total derivative. |
1447 |
|
|
1449 |
spherical coordinates: |
spherical coordinates: |
1450 |
|
|
1451 |
\begin{equation*} |
\begin{equation*} |
1452 |
\nabla \equiv \left( \frac{1}{r\cos \phi }\frac{\partial }{\partial \lambda }% |
\nabla \equiv \left( \frac{1}{r\cos \varphi }\frac{\partial }{\partial \lambda } |
1453 |
,\frac{1}{r}\frac{\partial }{\partial \phi },\frac{\partial }{\partial r}% |
,\frac{1}{r}\frac{\partial }{\partial \varphi },\frac{\partial }{\partial r} |
1454 |
\right) |
\right) |
1455 |
\end{equation*} |
\end{equation*} |
1456 |
|
|
1457 |
\begin{equation*} |
\begin{equation*} |
1458 |
\nabla .v\equiv \frac{1}{r\cos \phi }\left\{ \frac{\partial u}{\partial |
\nabla .v\equiv \frac{1}{r\cos \varphi }\left\{ \frac{\partial u}{\partial |
1459 |
\lambda }+\frac{\partial }{\partial \phi }\left( v\cos \phi \right) \right\} |
\lambda }+\frac{\partial }{\partial \varphi }\left( v\cos \varphi \right) \right\} |
1460 |
+\frac{1}{r^{2}}\frac{\partial \left( r^{2}\dot{r}\right) }{\partial r} |
+\frac{1}{r^{2}}\frac{\partial \left( r^{2}\dot{r}\right) }{\partial r} |
1461 |
\end{equation*} |
\end{equation*} |
1462 |
|
|
1463 |
%%%% \end{document} |
%tci%\end{document} |