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%%%% \part{MIT GCM basics} |
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%tci%\begin{document} |
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% Section: Overview |
% Section: Overview |
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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 |
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\marginpar{ |
\marginpar{ |
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Fig.1 One model}\ref{fig:onemodel} |
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 |
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\marginpar{ |
\marginpar{ |
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Fig.2 All scales}\ref{fig:all-scales} |
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 |
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\marginpar{ |
\marginpar{ |
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Fig.3 Finite volumes}\ref{fig:Finite volumes} |
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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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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A novel feature of MITgcm is its ability to simulate both atmospheric and |
A novel feature of MITgcm is its ability to simulate both atmospheric and |
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oceanographic flows at both small and large scales. |
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$mb$ |
Fig.E1a.\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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\input{part1/cubic_eddies_figure} |
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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 gridding 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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A regular spherical lat-lon grid can also be used. |
A regular spherical lat-lon grid can also be used. |
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\input{part1/hs_zave_u_figure} |
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\subsection{Ocean gyres} |
\subsection{Ocean gyres} |
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Baroclinic instability is a ubiquitous process in the ocean, as well as the |
Baroclinic instability is a ubiquitous process in the ocean, as well as the |
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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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\input{part1/ocean_gyres_figure} |
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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$^{\circ }$ |
Fig.E2a shows the pattern of ocean currents at the surface of a 4$^{\circ }$ |
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Fig.E2b shows the meridional overturning circulation of the global ocean in |
Fig.E2b shows the meridional overturning circulation of the global ocean in |
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Sverdrups. |
Sverdrups. |
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\input{part1/global_circ_figure} |
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\subsection{Convection and mixing over topography} |
\subsection{Convection and mixing over topography} |
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Dense plumes generated by localized cooling on the continental shelf of the |
Dense plumes generated by localized cooling on the continental shelf of the |
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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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\input{part1/convect_and_topo} |
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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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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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\input{part1/boundary_forced_waves} |
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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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As one example of application of the MITgcm adjoint, Fig.E4 maps the |
As one example of application of the MITgcm adjoint, Fig.E4 maps the |
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gradient $\frac{\partial J}{\partial \mathcal{H}}$where $J$ is the magnitude |
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 $% |
of the overturning streamfunction shown in fig?.? at 40$^{\circ }$N and $ |
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\mathcal{H}$ is the air-sea heat flux 100 years before. We see that $J$ is |
\mathcal{H}$ is the air-sea heat flux 100 years before. 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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\input{part1/adj_hf_ocean_figure} |
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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 obtained by bringing the model in to consistency with altimetric and |
ocean obtained by bringing the model in to consistency with altimetric and |
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in-situ observations over the period 1992-1997. |
in-situ observations over the period 1992-1997. |
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\input{part1/globes_figure} |
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\subsection{Ocean biogeochemical cycles} |
\subsection{Ocean biogeochemical cycles} |
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MITgcm is being used to study global biogeochemical cycles in the ocean. For |
MITgcm is being used to study global biogeochemical cycles in the ocean. For |
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flux of oxygen and its relation to density outcrops in the southern oceans |
flux of oxygen and its relation to density outcrops in the southern oceans |
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from a single year of a global, interannually varying simulation. |
from a single year of a global, interannually varying simulation. |
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Chris - get figure here: http://puddle.mit.edu/\symbol{126}% |
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mick/biogeochem.html |
\input{part1/biogeo_figure} |
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\subsection{Simulations of laboratory experiments} |
\subsection{Simulations of laboratory experiments} |
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arrested by its instability in a process analogous to that whic sets the |
arrested by its instability in a process analogous to that whic sets the |
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stratification of the ACC. |
stratification of the ACC. |
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% $Header$ |
% $Header$ |
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% $Name$ |
% $Name$ |
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To render atmosphere and ocean models from one dynamical core we exploit |
To render atmosphere and ocean models from one dynamical core we exploit |
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`isomorphisms' between equation sets that govern the evolution of the |
`isomorphisms' between equation sets that govern the evolution of the |
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respective fluids - see fig.4% |
respective fluids - see fig.4 |
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\marginpar{ |
\marginpar{ |
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Fig.4. Isomorphisms}. One system of hydrodynamical equations is written down |
Fig.4. Isomorphisms}. One system of hydrodynamical equations is written down |
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and encoded. The model variables have different interpretations depending on |
and encoded. The model variables have different interpretations depending on |
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vertical coordinate `$r$' is interpreted as pressure, $p$, if we are |
vertical coordinate `$r$' is interpreted as pressure, $p$, if we are |
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modeling the atmosphere and height, $z$, if we are modeling the ocean. |
modeling the atmosphere and height, $z$, if we are modeling the ocean. |
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\input{part1/zandpcoord_figure.tex} |
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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 |
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velocity $\vec{\mathbf{v}}$, active tracers $\theta $ and $S$, a |
velocity $\vec{\mathbf{v}}$, active tracers $\theta $ and $S$, a |
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`geopotential' $\phi $ and density $\rho =\rho (\theta ,S,p)$ which may |
`geopotential' $\phi $ and density $\rho =\rho (\theta ,S,p)$ which may |
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depend on $\theta $, $S$, and $p$. The equations that govern the evolution |
depend on $\theta $, $S$, and $p$. The equations that govern the evolution |
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of these fields, obtained by applying the laws of classical mechanics and |
of these fields, obtained by applying the laws of classical mechanics and |
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thermodynamics to a Boussinesq, Navier-Stokes fluid are, written in terms of |
thermodynamics to a Boussinesq, Navier-Stokes fluid are, written in terms of |
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a generic vertical coordinate, $r$, see fig.5% |
a generic vertical coordinate, $r$, see fig.5 |
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\marginpar{ |
\marginpar{ |
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Fig.5 The vertical coordinate of model}: |
Fig.5 The vertical coordinate of model}: |
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\begin{equation*} |
\begin{equation*} |
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\frac{D\vec{\mathbf{v}_{h}}}{Dt}+\left( 2\vec{\Omega}\times \vec{\mathbf{v}}% |
\frac{D\vec{\mathbf{v}_{h}}}{Dt}+\left( 2\vec{\Omega}\times \vec{\mathbf{v}} |
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\right) _{h}+\mathbf{\nabla }_{h}\phi =\mathcal{F}_{\vec{\mathbf{v}_{h}}}% |
\right) _{h}+\mathbf{\nabla }_{h}\phi =\mathcal{F}_{\vec{\mathbf{v}_{h}}} |
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\text{ horizontal mtm} |
\text{ horizontal mtm} |
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\end{equation*} |
\end{equation*} |
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\begin{equation*} |
\begin{equation*} |
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\frac{D\dot{r}}{Dt}+\widehat{k}\cdot \left( 2\vec{\Omega}\times \vec{\mathbf{% |
\frac{D\dot{r}}{Dt}+\widehat{k}\cdot \left( 2\vec{\Omega}\times \vec{\mathbf{ |
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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{ |
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vertical mtm} |
vertical mtm} |
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\end{equation*} |
\end{equation*} |
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\begin{equation} |
\begin{equation} |
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\mathbf{\nabla }_{h}\cdot \vec{\mathbf{v}}_{h}+\frac{\partial \dot{r}}{% |
\mathbf{\nabla }_{h}\cdot \vec{\mathbf{v}}_{h}+\frac{\partial \dot{r}}{ |
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\partial r}=0\text{ continuity} \label{eq:continuous} |
\partial r}=0\text{ continuity} \label{eq:continuous} |
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\end{equation} |
\end{equation} |
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\end{equation*} |
\end{equation*} |
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\begin{equation*} |
\begin{equation*} |
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\mathbf{\nabla }=\mathbf{\nabla }_{h}+\widehat{k}\frac{\partial }{\partial r}% |
\mathbf{\nabla }=\mathbf{\nabla }_{h}+\widehat{k}\frac{\partial }{\partial r} |
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\text{ is the `grad' operator} |
\text{ is the `grad' operator} |
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\end{equation*} |
\end{equation*} |
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with $\mathbf{\nabla }_{h}$ operating in the horizontal and $\widehat{k}% |
with $\mathbf{\nabla }_{h}$ operating in the horizontal and $\widehat{k} |
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\frac{\partial }{\partial r}$ operating in the vertical, where $\widehat{k}$ |
\frac{\partial }{\partial r}$ operating in the vertical, where $\widehat{k}$ |
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is a unit vector in the vertical |
is a unit vector in the vertical |
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\end{equation*} |
\end{equation*} |
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\begin{equation*} |
\begin{equation*} |
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\mathcal{F}_{\vec{\mathbf{v}}}\text{ are forcing and dissipation of }\vec{% |
\mathcal{F}_{\vec{\mathbf{v}}}\text{ are forcing and dissipation of }\vec{ |
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\mathbf{v}} |
\mathbf{v}} |
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\end{equation*} |
\end{equation*} |
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\begin{equation} |
\begin{equation} |
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\vec{\mathbf{v}}\cdot \vec{\mathbf{n}}=0 \label{eq:noflow} |
\vec{\mathbf{v}}\cdot \vec{\mathbf{n}}=0 \label{eq:noflow} |
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\end{equation}% |
\end{equation} |
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where $\vec{\mathbf{n}}$ is the normal to a solid boundary. |
where $\vec{\mathbf{n}}$ is the normal to a solid boundary. |
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\subsection{Atmosphere} |
\subsection{Atmosphere} |
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\begin{equation*} |
\begin{equation*} |
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T\text{ is absolute temperature} |
T\text{ is absolute temperature} |
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\end{equation*}% |
\end{equation*} |
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\begin{equation*} |
\begin{equation*} |
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p\text{ is the pressure} |
p\text{ is the pressure} |
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\end{equation*}% |
\end{equation*} |
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\begin{eqnarray*} |
\begin{eqnarray*} |
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&&z\text{ is the height of the pressure surface} \\ |
&&z\text{ is the height of the pressure surface} \\ |
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&&g\text{ is the acceleration due to gravity} |
&&g\text{ is the acceleration due to gravity} |
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the Exner function $\Pi (p)$ given by (see Appendix Atmosphere) |
the Exner function $\Pi (p)$ given by (see Appendix Atmosphere) |
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\begin{equation} |
\begin{equation} |
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\Pi (p)=c_{p}(\frac{p}{p_{c}})^{\kappa } \label{eq:exner} |
\Pi (p)=c_{p}(\frac{p}{p_{c}})^{\kappa } \label{eq:exner} |
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\end{equation}% |
\end{equation} |
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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 |
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constant and $c_{p}$ the specific heat of air at constant pressure. |
constant and $c_{p}$ the specific heat of air at constant pressure. |
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The surface of the ocean is given by: $R_{moving}=\eta $ |
The surface of the ocean is given by: $R_{moving}=\eta $ |
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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 $ |
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R_{o}=Z_{o}=0$. |
R_{o}=Z_{o}=0$. |
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Boundary conditions are: |
Boundary conditions are: |
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\begin{eqnarray} |
\begin{eqnarray} |
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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} |
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\\ |
\\ |
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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) |
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\label{eq:moving-bc-ocean}} |
\label{eq:moving-bc-ocean}} |
555 |
\end{eqnarray} |
\end{eqnarray} |
556 |
where $\eta $ is the elevation of the free surface. |
where $\eta $ is the elevation of the free surface. |
567 |
\begin{equation} |
\begin{equation} |
568 |
\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) |
569 |
\label{eq:phi-split} |
\label{eq:phi-split} |
570 |
\end{equation}% |
\end{equation} |
571 |
and write eq(\ref{incompressible}a,b) in the form: |
and write eq(\ref{incompressible}a,b) in the form: |
572 |
|
|
573 |
\begin{equation} |
\begin{equation} |
581 |
\end{equation} |
\end{equation} |
582 |
|
|
583 |
\begin{equation} |
\begin{equation} |
584 |
\epsilon _{nh}\frac{\partial \dot{r}}{\partial t}+\frac{\partial \phi _{nh}}{% |
\epsilon _{nh}\frac{\partial \dot{r}}{\partial t}+\frac{\partial \phi _{nh}}{ |
585 |
\partial r}=G_{\dot{r}} \label{eq:mom-w} |
\partial r}=G_{\dot{r}} \label{eq:mom-w} |
586 |
\end{equation} |
\end{equation} |
587 |
Here $\epsilon _{nh}$ is a non-hydrostatic parameter. |
Here $\epsilon _{nh}$ is a non-hydrostatic parameter. |
588 |
|
|
589 |
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 |
590 |
{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 |
591 |
terms in the momentum equations. In spherical coordinates they take the form% |
terms in the momentum equations. In spherical coordinates they take the form |
592 |
\footnote{% |
\footnote{ |
593 |
In the hydrostatic primitive equations (\textbf{HPE}) all underlined terms |
In the hydrostatic primitive equations (\textbf{HPE}) all underlined terms |
594 |
in (\ref{eq:gu-speherical}), (\ref{eq:gv-spherical}) and (\ref% |
in (\ref{eq:gu-speherical}), (\ref{eq:gv-spherical}) and (\ref |
595 |
{eq:gw-spherical}) are omitted; the singly-underlined terms are included in |
{eq:gw-spherical}) are omitted; the singly-underlined terms are included in |
596 |
the quasi-hydrostatic model (\textbf{QH}). The fully non-hydrostatic model (% |
the quasi-hydrostatic model (\textbf{QH}). The fully non-hydrostatic model ( |
597 |
\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 |
598 |
discussion: |
discussion: |
599 |
|
|
601 |
\left. |
\left. |
602 |
\begin{tabular}{l} |
\begin{tabular}{l} |
603 |
$G_{u}=-\vec{\mathbf{v}}.\nabla u$ \\ |
$G_{u}=-\vec{\mathbf{v}}.\nabla u$ \\ |
604 |
$-\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\} $ |
605 |
\\ |
\\ |
606 |
$-\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\} $ |
607 |
\\ |
\\ |
608 |
$+\mathcal{F}_{u}$% |
$+\mathcal{F}_{u}$ |
609 |
\end{tabular}% |
\end{tabular} |
610 |
\ \right\} \left\{ |
\ \right\} \left\{ |
611 |
\begin{tabular}{l} |
\begin{tabular}{l} |
612 |
\textit{advection} \\ |
\textit{advection} \\ |
613 |
\textit{metric} \\ |
\textit{metric} \\ |
614 |
\textit{Coriolis} \\ |
\textit{Coriolis} \\ |
615 |
\textit{\ Forcing/Dissipation}% |
\textit{\ Forcing/Dissipation} |
616 |
\end{tabular}% |
\end{tabular} |
617 |
\ \right. \qquad \label{eq:gu-speherical} |
\ \right. \qquad \label{eq:gu-speherical} |
618 |
\end{equation} |
\end{equation} |
619 |
|
|
621 |
\left. |
\left. |
622 |
\begin{tabular}{l} |
\begin{tabular}{l} |
623 |
$G_{v}=-\vec{\mathbf{v}}.\nabla v$ \\ |
$G_{v}=-\vec{\mathbf{v}}.\nabla v$ \\ |
624 |
$-\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\} |
625 |
$ \\ |
$ \\ |
626 |
$-\left\{ -2\Omega u\sin lat\right\} $ \\ |
$-\left\{ -2\Omega u\sin \varphi \right\} $ \\ |
627 |
$+\mathcal{F}_{v}$% |
$+\mathcal{F}_{v}$ |
628 |
\end{tabular}% |
\end{tabular} |
629 |
\ \right\} \left\{ |
\ \right\} \left\{ |
630 |
\begin{tabular}{l} |
\begin{tabular}{l} |
631 |
\textit{advection} \\ |
\textit{advection} \\ |
632 |
\textit{metric} \\ |
\textit{metric} \\ |
633 |
\textit{Coriolis} \\ |
\textit{Coriolis} \\ |
634 |
\textit{\ Forcing/Dissipation}% |
\textit{\ Forcing/Dissipation} |
635 |
\end{tabular}% |
\end{tabular} |
636 |
\ \right. \qquad \label{eq:gv-spherical} |
\ \right. \qquad \label{eq:gv-spherical} |
637 |
\end{equation}% |
\end{equation} |
638 |
\qquad \qquad \qquad \qquad \qquad |
\qquad \qquad \qquad \qquad \qquad |
639 |
|
|
640 |
\begin{equation} |
\begin{equation} |
642 |
\begin{tabular}{l} |
\begin{tabular}{l} |
643 |
$G_{\dot{r}}=-\underline{\underline{\vec{\mathbf{v}}.\nabla \dot{r}}}$ \\ |
$G_{\dot{r}}=-\underline{\underline{\vec{\mathbf{v}}.\nabla \dot{r}}}$ \\ |
644 |
$+\left\{ \underline{\frac{u^{_{^{2}}}+v^{2}}{{r}}}\right\} $ \\ |
$+\left\{ \underline{\frac{u^{_{^{2}}}+v^{2}}{{r}}}\right\} $ \\ |
645 |
${+}\underline{{2\Omega u\cos lat}}$ \\ |
${+}\underline{{2\Omega u\cos \varphi}}$ \\ |
646 |
$\underline{\underline{\mathcal{F}_{\dot{r}}}}$% |
$\underline{\underline{\mathcal{F}_{\dot{r}}}}$ |
647 |
\end{tabular}% |
\end{tabular} |
648 |
\ \right\} \left\{ |
\ \right\} \left\{ |
649 |
\begin{tabular}{l} |
\begin{tabular}{l} |
650 |
\textit{advection} \\ |
\textit{advection} \\ |
651 |
\textit{metric} \\ |
\textit{metric} \\ |
652 |
\textit{Coriolis} \\ |
\textit{Coriolis} \\ |
653 |
\textit{\ Forcing/Dissipation}% |
\textit{\ Forcing/Dissipation} |
654 |
\end{tabular}% |
\end{tabular} |
655 |
\ \right. \label{eq:gw-spherical} |
\ \right. \label{eq:gw-spherical} |
656 |
\end{equation}% |
\end{equation} |
657 |
\qquad \qquad \qquad \qquad \qquad |
\qquad \qquad \qquad \qquad \qquad |
658 |
|
|
659 |
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 `$\varphi$ |
660 |
' is latitude. |
' is latitude. |
661 |
|
|
662 |
Grad and div operators in spherical coordinates are defined in appendix |
Grad and div operators in spherical coordinates are defined in appendix |
663 |
OPERATORS.% |
OPERATORS. |
664 |
\marginpar{ |
\marginpar{ |
665 |
Fig.6 Spherical polar coordinate system.} |
Fig.6 Spherical polar coordinate system.} |
666 |
|
|
667 |
|
%%CNHbegin |
668 |
|
\input{part1/sphere_coord_figure.tex} |
669 |
|
%%CNHend |
670 |
|
|
671 |
\subsubsection{Shallow atmosphere approximation} |
\subsubsection{Shallow atmosphere approximation} |
672 |
|
|
673 |
Most models are based on the `hydrostatic primitive equations' (HPE's) in |
Most models are based on the `hydrostatic primitive equations' (HPE's) in |
676 |
Coriolis force is treated approximately and the shallow atmosphere |
Coriolis force is treated approximately and the shallow atmosphere |
677 |
approximation is made.\ The MITgcm need not make the `traditional |
approximation is made.\ The MITgcm need not make the `traditional |
678 |
approximation'. To be able to support consistent non-hydrostatic forms the |
approximation'. To be able to support consistent non-hydrostatic forms the |
679 |
shallow atmosphere approximation can be relaxed - when dividing through by $% |
shallow atmosphere approximation can be relaxed - when dividing through by $ |
680 |
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 $a$, |
681 |
the radius of the earth. |
the radius of the earth. |
682 |
|
|
689 |
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 |
690 |
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 |
691 |
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 |
692 |
computed at all other levels by integration of the hydrostatic relation, eq(% |
computed at all other levels by integration of the hydrostatic relation, eq( |
693 |
\ref{eq:hydrostatic}). |
\ref{eq:hydrostatic}). |
694 |
|
|
695 |
In the `quasi-hydrostatic' equations (\textbf{QH)} strict balance between |
In the `quasi-hydrostatic' equations (\textbf{QH)} strict balance between |
696 |
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 |
697 |
\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 |
698 |
contribution to the pressure field: only the terms underlined twice in Eqs. (% |
contribution to the pressure field: only the terms underlined twice in Eqs. ( |
699 |
\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 |
700 |
and, simultaneously, the shallow atmosphere approximation is relaxed. In |
and, simultaneously, the shallow atmosphere approximation is relaxed. In |
701 |
\textbf{QH}\ \textit{all} the metric terms are retained and the full |
\textbf{QH}\ \textit{all} the metric terms are retained and the full |
703 |
vertical momentum equation (\ref{eq:mom-w}) becomes: |
vertical momentum equation (\ref{eq:mom-w}) becomes: |
704 |
|
|
705 |
\begin{equation*} |
\begin{equation*} |
706 |
\frac{\partial \phi _{nh}}{\partial r}=2\Omega u\cos lat |
\frac{\partial \phi _{nh}}{\partial r}=2\Omega u\cos \varphi |
707 |
\end{equation*} |
\end{equation*} |
708 |
making a small correction to the hydrostatic pressure. |
making a small correction to the hydrostatic pressure. |
709 |
|
|
719 |
|
|
720 |
\paragraph{Non-hydrostatic Ocean} |
\paragraph{Non-hydrostatic Ocean} |
721 |
|
|
722 |
In the non-hydrostatic ocean model all terms in equations Eqs.(\ref% |
In the non-hydrostatic ocean model all terms in equations Eqs.(\ref |
723 |
{eq:gu-speherical} $\rightarrow $\ \ref{eq:gw-spherical}) are retained. A |
{eq:gu-speherical} $\rightarrow $\ \ref{eq:gw-spherical}) are retained. A |
724 |
three dimensional elliptic equation must be solved subject to Neumann |
three dimensional elliptic equation must be solved subject to Neumann |
725 |
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 |
732 |
|
|
733 |
\paragraph{Quasi-nonhydrostatic Atmosphere} |
\paragraph{Quasi-nonhydrostatic Atmosphere} |
734 |
|
|
735 |
In the non-hydrostatic version of our atmospheric model we approximate $\dot{% |
In the non-hydrostatic version of our atmospheric model we approximate $\dot{ |
736 |
r}$ 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}) |
737 |
(but only here) by: |
(but only here) by: |
738 |
|
|
739 |
\begin{equation} |
\begin{equation} |
740 |
\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} |
741 |
\end{equation}% |
\end{equation} |
742 |
where $p_{hy}$ is the hydrostatic pressure. |
where $p_{hy}$ is the hydrostatic pressure. |
743 |
|
|
744 |
\subsubsection{Summary of equation sets supported by model} |
\subsubsection{Summary of equation sets supported by model} |
766 |
|
|
767 |
\subparagraph{Non-hydrostatic} |
\subparagraph{Non-hydrostatic} |
768 |
|
|
769 |
Non-hydrostatic forms of the incompressible Boussinesq equations in $z-$% |
Non-hydrostatic forms of the incompressible Boussinesq equations in $z-$ |
770 |
coordinates are supported - see eqs(\ref{eq:ocean-mom}) to (\ref% |
coordinates are supported - see eqs(\ref{eq:ocean-mom}) to (\ref |
771 |
{eq:ocean-salt}). |
{eq:ocean-salt}). |
772 |
|
|
773 |
\subsection{Solution strategy} |
\subsection{Solution strategy} |
774 |
|
|
775 |
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{ |
776 |
NH} models is summarized in Fig.7.% |
NH} models is summarized in Fig.7. |
777 |
\marginpar{ |
\marginpar{ |
778 |
Fig.7 Solution strategy} Under all dynamics, a 2-d elliptic equation is |
Fig.7 Solution strategy} Under all dynamics, a 2-d elliptic equation is |
779 |
first solved to find the surface pressure and the hydrostatic pressure at |
first solved to find the surface pressure and the hydrostatic pressure at |
784 |
stepping forward the horizontal momentum equations; $\dot{r}$ is found by |
stepping forward the horizontal momentum equations; $\dot{r}$ is found by |
785 |
stepping forward the vertical momentum equation. |
stepping forward the vertical momentum equation. |
786 |
|
|
787 |
|
%%CNHbegin |
788 |
|
\input{part1/solution_strategy_figure.tex} |
789 |
|
%%CNHend |
790 |
|
|
791 |
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 |
792 |
course, some complication that goes with the inclusion of $\cos \phi \ $% |
course, some complication that goes with the inclusion of $\cos \varphi \ $ |
793 |
Coriolis terms and the relaxation of the shallow atmosphere approximation. |
Coriolis terms and the relaxation of the shallow atmosphere approximation. |
794 |
But this leads to negligible increase in computation. In \textbf{NH}, in |
But this leads to negligible increase in computation. In \textbf{NH}, in |
795 |
contrast, one additional elliptic equation - a three-dimensional one - must |
contrast, one additional elliptic equation - a three-dimensional one - must |
813 |
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: |
814 |
|
|
815 |
\begin{equation*} |
\begin{equation*} |
816 |
\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} |
817 |
\right] _{r}^{R_{o}}=\int_{r}^{R_{o}}-bdr |
\right] _{r}^{R_{o}}=\int_{r}^{R_{o}}-bdr |
818 |
\end{equation*} |
\end{equation*} |
819 |
and so |
and so |
831 |
|
|
832 |
\subsubsection{Surface pressure} |
\subsubsection{Surface pressure} |
833 |
|
|
834 |
The surface pressure equation can be obtained by integrating continuity, (% |
The surface pressure equation can be obtained by integrating continuity, ( |
835 |
\ref{eq:continuous})c, vertically from $r=R_{fixed}$ to $r=R_{moving}$ |
\ref{eq:continuous})c, vertically from $r=R_{fixed}$ to $r=R_{moving}$ |
836 |
|
|
837 |
\begin{equation*} |
\begin{equation*} |
838 |
\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} |
839 |
}_{h}+\partial _{r}\dot{r}\right) dr=0 |
}_{h}+\partial _{r}\dot{r}\right) dr=0 |
840 |
\end{equation*} |
\end{equation*} |
841 |
|
|
843 |
|
|
844 |
\begin{equation*} |
\begin{equation*} |
845 |
\frac{\partial \eta }{\partial t}+\vec{\mathbf{v}}.\nabla \eta |
\frac{\partial \eta }{\partial t}+\vec{\mathbf{v}}.\nabla \eta |
846 |
+\int_{R_{fixed}}^{R_{moving}}\mathbf{\nabla }_{h}\cdot \vec{\mathbf{v}}% |
+\int_{R_{fixed}}^{R_{moving}}\mathbf{\nabla }_{h}\cdot \vec{\mathbf{v}} |
847 |
_{h}dr=0 |
_{h}dr=0 |
848 |
\end{equation*} |
\end{equation*} |
849 |
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 $ |
850 |
r $. The above can be rearranged to yield, using Leibnitz's theorem: |
r $. The above can be rearranged to yield, using Leibnitz's theorem: |
851 |
|
|
852 |
\begin{equation} |
\begin{equation} |
853 |
\frac{\partial \eta }{\partial t}+\mathbf{\nabla }_{h}\cdot |
\frac{\partial \eta }{\partial t}+\mathbf{\nabla }_{h}\cdot |
854 |
\int_{R_{fixed}}^{R_{moving}}\vec{\mathbf{v}}_{h}dr=\text{source} |
\int_{R_{fixed}}^{R_{moving}}\vec{\mathbf{v}}_{h}dr=\text{source} |
855 |
\label{eq:free-surface} |
\label{eq:free-surface} |
856 |
\end{equation}% |
\end{equation} |
857 |
where we have incorporated a source term. |
where we have incorporated a source term. |
858 |
|
|
859 |
Whether $\phi $ is pressure (ocean model, $p/\rho _{c}$) or geopotential |
Whether $\phi $ is pressure (ocean model, $p/\rho _{c}$) or geopotential |
862 |
\begin{equation} |
\begin{equation} |
863 |
\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) |
864 |
\label{eq:phi-surf} |
\label{eq:phi-surf} |
865 |
\end{equation}% |
\end{equation} |
866 |
where $b_{s}$ is the buoyancy at the surface. |
where $b_{s}$ is the buoyancy at the surface. |
867 |
|
|
868 |
In the hydrostatic limit ($\epsilon _{nh}=0$), Eqs(\ref{eq:mom-h}), (\ref% |
In the hydrostatic limit ($\epsilon _{nh}=0$), Eqs(\ref{eq:mom-h}), (\ref |
869 |
{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 |
870 |
elliptic equation for $\phi _{s}$ as described in Chapter 2. Both `free |
elliptic equation for $\phi _{s}$ as described in Chapter 2. Both `free |
871 |
surface' and `rigid lid' approaches are available. |
surface' and `rigid lid' approaches are available. |
872 |
|
|
873 |
\subsubsection{Non-hydrostatic pressure} |
\subsubsection{Non-hydrostatic pressure} |
874 |
|
|
875 |
Taking the horizontal divergence of (\ref{hor-mtm}) and adding $\frac{% |
Taking the horizontal divergence of (\ref{hor-mtm}) and adding $\frac{ |
876 |
\partial }{\partial r}$ of (\ref{vertmtm}), invoking the continuity equation |
\partial }{\partial r}$ of (\ref{vertmtm}), invoking the continuity equation |
877 |
(\ref{incompressible}), we deduce that: |
(\ref{incompressible}), we deduce that: |
878 |
|
|
879 |
\begin{equation} |
\begin{equation} |
880 |
\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{ |
881 |
\nabla }_{h}^{2}\phi _{s}+\mathbf{\nabla }^{2}\phi _{hyd}\right) =\nabla .% |
\nabla }_{h}^{2}\phi _{s}+\mathbf{\nabla }^{2}\phi _{hyd}\right) =\nabla . |
882 |
\vec{\mathbf{F}} \label{eq:3d-invert} |
\vec{\mathbf{F}} \label{eq:3d-invert} |
883 |
\end{equation} |
\end{equation} |
884 |
|
|
898 |
\end{equation} |
\end{equation} |
899 |
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 |
900 |
kinematic condition (\ref{nonormalflow}) is also applied to the vertical |
kinematic condition (\ref{nonormalflow}) is also applied to the vertical |
901 |
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 $ |
902 |
\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 |
903 |
tangential component of velocity, $v_{T}$, at all solid boundaries, |
tangential component of velocity, $v_{T}$, at all solid boundaries, |
904 |
depending on the form chosen for the dissipative terms in the momentum |
depending on the form chosen for the dissipative terms in the momentum |
915 |
\begin{equation*} |
\begin{equation*} |
916 |
\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 |
917 |
_{s}+\mathbf{\nabla }\phi _{hyd}\right) |
_{s}+\mathbf{\nabla }\phi _{hyd}\right) |
918 |
\end{equation*}% |
\end{equation*} |
919 |
presenting inhomogeneous Neumann boundary conditions to the Elliptic problem |
presenting inhomogeneous Neumann boundary conditions to the Elliptic problem |
920 |
(\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 |
921 |
exploit classical 3D potential theory and, by introducing an appropriately |
exploit classical 3D potential theory and, by introducing an appropriately |
922 |
chosen $\delta $-function sheet of `source-charge', replace the |
chosen $\delta $-function sheet of `source-charge', replace the |
923 |
inhomogeneous boundary condition on pressure by a homogeneous one. The |
inhomogeneous boundary condition on pressure by a homogeneous one. The |
924 |
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 $ |
925 |
\vec{\mathbf{F}}.$ By simultaneously setting $% |
\vec{\mathbf{F}}.$ By simultaneously setting $ |
926 |
\begin{array}{l} |
\begin{array}{l} |
927 |
\widehat{n}.\vec{\mathbf{F}}% |
\widehat{n}.\vec{\mathbf{F}} |
928 |
\end{array}% |
\end{array} |
929 |
=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 |
930 |
self-consistent but simpler homogenized Elliptic problem is obtained: |
self-consistent but simpler homogenized Elliptic problem is obtained: |
931 |
|
|
932 |
\begin{equation*} |
\begin{equation*} |
933 |
\nabla ^{2}\phi _{nh}=\nabla .\widetilde{\vec{\mathbf{F}}}\qquad |
\nabla ^{2}\phi _{nh}=\nabla .\widetilde{\vec{\mathbf{F}}}\qquad |
934 |
\end{equation*}% |
\end{equation*} |
935 |
where $\widetilde{\vec{\mathbf{F}}}$ is a modified $\vec{\mathbf{F}}$ such |
where $\widetilde{\vec{\mathbf{F}}}$ is a modified $\vec{\mathbf{F}}$ such |
936 |
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 |
937 |
{eq:inhom-neumann-nh}) the modified boundary condition becomes: |
{eq:inhom-neumann-nh}) the modified boundary condition becomes: |
938 |
|
|
939 |
\begin{equation} |
\begin{equation} |
962 |
biharmonic frictions are commonly used: |
biharmonic frictions are commonly used: |
963 |
|
|
964 |
\begin{equation} |
\begin{equation} |
965 |
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}} |
966 |
+A_{4}\nabla _{h}^{4}v \label{eq:dissipation} |
+A_{4}\nabla _{h}^{4}v \label{eq:dissipation} |
967 |
\end{equation} |
\end{equation} |
968 |
where $A_{h}$ and $A_{v}\ $are (constant) horizontal and vertical viscosity |
where $A_{h}$ and $A_{v}\ $are (constant) horizontal and vertical viscosity |
973 |
|
|
974 |
The mixing terms for the temperature and salinity equations have a similar |
The mixing terms for the temperature and salinity equations have a similar |
975 |
form to that of momentum except that the diffusion tensor can be |
form to that of momentum except that the diffusion tensor can be |
976 |
non-diagonal and have varying coefficients. $\qquad $% |
non-diagonal and have varying coefficients. $\qquad $ |
977 |
\begin{equation} |
\begin{equation} |
978 |
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 |
979 |
_{h}^{4}(T,S) \label{eq:diffusion} |
_{h}^{4}(T,S) \label{eq:diffusion} |
980 |
\end{equation} |
\end{equation} |
981 |
where $\underline{\underline{K}}\ $is the diffusion tensor and the $K_{4}\ $% |
where $\underline{\underline{K}}\ $is the diffusion tensor and the $K_{4}\ $ |
982 |
horizontal coefficient for biharmonic diffusion. In the simplest case where |
horizontal coefficient for biharmonic diffusion. In the simplest case where |
983 |
the subgrid-scale fluxes of heat and salt are parameterized with constant |
the subgrid-scale fluxes of heat and salt are parameterized with constant |
984 |
horizontal and vertical diffusion coefficients, $\underline{\underline{K}}$, |
horizontal and vertical diffusion coefficients, $\underline{\underline{K}}$, |
989 |
\begin{array}{ccc} |
\begin{array}{ccc} |
990 |
K_{h} & 0 & 0 \\ |
K_{h} & 0 & 0 \\ |
991 |
0 & K_{h} & 0 \\ |
0 & K_{h} & 0 \\ |
992 |
0 & 0 & K_{v}% |
0 & 0 & K_{v} |
993 |
\end{array} |
\end{array} |
994 |
\right) \qquad \qquad \qquad \label{eq:diagonal-diffusion-tensor} |
\right) \qquad \qquad \qquad \label{eq:diagonal-diffusion-tensor} |
995 |
\end{equation} |
\end{equation} |
999 |
|
|
1000 |
\subsection{Vector invariant form} |
\subsection{Vector invariant form} |
1001 |
|
|
1002 |
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 |
1003 |
{hor-mtm}) and (\ref{vertmtm}) in the (so-called) `vector invariant' form: |
{hor-mtm}) and (\ref{vertmtm}) in the (so-called) `vector invariant' form: |
1004 |
|
|
1005 |
\begin{equation} |
\begin{equation} |
1006 |
\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} |
1007 |
+\left( \nabla \times \vec{\mathbf{v}}\right) \times \vec{\mathbf{v}}+\nabla % |
+\left( \nabla \times \vec{\mathbf{v}}\right) \times \vec{\mathbf{v}}+\nabla |
1008 |
\left[ \frac{1}{2}(\vec{\mathbf{v}}\cdot \vec{\mathbf{v}})\right] |
\left[ \frac{1}{2}(\vec{\mathbf{v}}\cdot \vec{\mathbf{v}})\right] |
1009 |
\label{eq:vi-identity} |
\label{eq:vi-identity} |
1010 |
\end{equation}% |
\end{equation} |
1011 |
This permits alternative numerical treatments of the non-linear terms based |
This permits alternative numerical treatments of the non-linear terms based |
1012 |
on their representation as a vorticity flux. Because gradients of coordinate |
on their representation as a vorticity flux. Because gradients of coordinate |
1013 |
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 |
1014 |
representation of the metric terms in (\ref{eq:gu-speherical}), (\ref% |
representation of the metric terms in (\ref{eq:gu-speherical}), (\ref |
1015 |
{eq:gv-spherical}) and (\ref{eq:gw-spherical}), can be avoided: information |
{eq:gv-spherical}) and (\ref{eq:gw-spherical}), can be avoided: information |
1016 |
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 |
1017 |
to discretize the model. |
to discretize the model. |
1033 |
|
|
1034 |
The hydrostatic primitive equations (HPEs) in p-coordinates are: |
The hydrostatic primitive equations (HPEs) in p-coordinates are: |
1035 |
\begin{eqnarray} |
\begin{eqnarray} |
1036 |
\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}} |
1037 |
_{h}+\mathbf{\nabla }_{p}\phi &=&\vec{\mathbf{\mathcal{F}}} |
_{h}+\mathbf{\nabla }_{p}\phi &=&\vec{\mathbf{\mathcal{F}}} |
1038 |
\label{eq:atmos-mom} \\ |
\label{eq:atmos-mom} \\ |
1039 |
\frac{\partial \phi }{\partial p}+\alpha &=&0 \label{eq-p-hydro-start} \\ |
\frac{\partial \phi }{\partial p}+\alpha &=&0 \label{eq-p-hydro-start} \\ |
1040 |
\mathbf{\nabla }_{p}\cdot \vec{\mathbf{v}}_{h}+\frac{\partial \omega }{% |
\mathbf{\nabla }_{p}\cdot \vec{\mathbf{v}}_{h}+\frac{\partial \omega }{ |
1041 |
\partial p} &=&0 \label{eq:atmos-cont} \\ |
\partial p} &=&0 \label{eq:atmos-cont} \\ |
1042 |
p\alpha &=&RT \label{eq:atmos-eos} \\ |
p\alpha &=&RT \label{eq:atmos-eos} \\ |
1043 |
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} |
1044 |
\end{eqnarray}% |
\end{eqnarray} |
1045 |
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 |
1046 |
surfaces) component of velocity,$\frac{D}{Dt}=\vec{\mathbf{v}}_{h}\cdot |
surfaces) component of velocity,$\frac{D}{Dt}=\vec{\mathbf{v}}_{h}\cdot |
1047 |
\mathbf{\nabla }_{p}+\omega \frac{\partial }{\partial p}$ is the total |
\mathbf{\nabla }_{p}+\omega \frac{\partial }{\partial p}$ is the total |
1048 |
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 |
1049 |
the geopotential, $\alpha =1/\rho $ is the specific volume, $\omega =\frac{Dp% |
the geopotential, $\alpha =1/\rho $ is the specific volume, $\omega =\frac{Dp |
1050 |
}{Dt}$ is the vertical velocity in the $p-$coordinate. Equation(\ref% |
}{Dt}$ is the vertical velocity in the $p-$coordinate. Equation(\ref |
1051 |
{eq:atmos-heat}) is the first law of thermodynamics where internal energy $% |
{eq:atmos-heat}) is the first law of thermodynamics where internal energy $ |
1052 |
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 $ |
1053 |
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. |
1054 |
|
|
1055 |
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 |
1057 |
Differentiating (\ref{eq:atmos-eos}) we get: |
Differentiating (\ref{eq:atmos-eos}) we get: |
1058 |
\begin{equation*} |
\begin{equation*} |
1059 |
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} |
1060 |
\end{equation*}% |
\end{equation*} |
1061 |
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 $ |
1062 |
c_{p}=c_{v}+R$, gives: |
c_{p}=c_{v}+R$, gives: |
1063 |
\begin{equation} |
\begin{equation} |
1064 |
c_{p}\frac{DT}{Dt}-\alpha \frac{Dp}{Dt}=\mathcal{Q} |
c_{p}\frac{DT}{Dt}-\alpha \frac{Dp}{Dt}=\mathcal{Q} |
1065 |
\label{eq-p-heat-interim} |
\label{eq-p-heat-interim} |
1066 |
\end{equation}% |
\end{equation} |
1067 |
Potential temperature is defined: |
Potential temperature is defined: |
1068 |
\begin{equation} |
\begin{equation} |
1069 |
\theta =T(\frac{p_{c}}{p})^{\kappa } \label{eq:potential-temp} |
\theta =T(\frac{p_{c}}{p})^{\kappa } \label{eq:potential-temp} |
1070 |
\end{equation}% |
\end{equation} |
1071 |
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 |
1072 |
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: |
1073 |
\begin{equation} |
\begin{equation} |
1074 |
\Pi (p)=c_{p}(\frac{p}{p_{c}})^{\kappa } \label{Exner} |
\Pi (p)=c_{p}(\frac{p}{p_{c}})^{\kappa } \label{Exner} |
1075 |
\end{equation}% |
\end{equation} |
1076 |
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 |
1077 |
the Exner function: |
the Exner function: |
1078 |
\begin{equation*} |
\begin{equation*} |
1079 |
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 |
1080 |
}{p}\;\;;\;\;\alpha =\frac{\kappa \Pi \theta }{p}=\frac{\partial \ \Pi }{% |
}{p}\;\;;\;\;\alpha =\frac{\kappa \Pi \theta }{p}=\frac{\partial \ \Pi }{ |
1081 |
\partial p}\theta \;\;;\;\;\frac{D\Pi }{Dt}=\frac{\partial \Pi }{\partial p}% |
\partial p}\theta \;\;;\;\;\frac{D\Pi }{Dt}=\frac{\partial \Pi }{\partial p} |
1082 |
\frac{Dp}{Dt} |
\frac{Dp}{Dt} |
1083 |
\end{equation*}% |
\end{equation*} |
1084 |
where $b=\frac{\partial \ \Pi }{\partial p}\theta $ is the buoyancy. |
where $b=\frac{\partial \ \Pi }{\partial p}\theta $ is the buoyancy. |
1085 |
|
|
1086 |
The heat equation is obtained by noting that |
The heat equation is obtained by noting that |
1095 |
\end{equation} |
\end{equation} |
1096 |
which is in conservative form. |
which is in conservative form. |
1097 |
|
|
1098 |
For convenience in the model we prefer to step forward (\ref% |
For convenience in the model we prefer to step forward (\ref |
1099 |
{eq:potential-temperature-equation}) rather than (\ref{eq:atmos-heat}). |
{eq:potential-temperature-equation}) rather than (\ref{eq:atmos-heat}). |
1100 |
|
|
1101 |
\subsubsection{Boundary conditions} |
\subsubsection{Boundary conditions} |
1139 |
|
|
1140 |
The final form of the HPE's in p coordinates is then: |
The final form of the HPE's in p coordinates is then: |
1141 |
\begin{eqnarray} |
\begin{eqnarray} |
1142 |
\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}} |
1143 |
_{h}+\mathbf{\nabla }_{p}\phi ^{\prime } &=&\vec{\mathbf{\mathcal{F}}} \\ |
_{h}+\mathbf{\nabla }_{p}\phi ^{\prime } &=&\vec{\mathbf{\mathcal{F}}} \\ |
1144 |
\frac{\partial \phi ^{\prime }}{\partial p}+\alpha ^{\prime } &=&0 \\ |
\frac{\partial \phi ^{\prime }}{\partial p}+\alpha ^{\prime } &=&0 \\ |
1145 |
\mathbf{\nabla }_{p}\cdot \vec{\mathbf{v}}_{h}+\frac{\partial \omega }{% |
\mathbf{\nabla }_{p}\cdot \vec{\mathbf{v}}_{h}+\frac{\partial \omega }{ |
1146 |
\partial p} &=&0 \\ |
\partial p} &=&0 \\ |
1147 |
\frac{\partial \Pi }{\partial p}\theta ^{\prime } &=&\alpha ^{\prime } \\ |
\frac{\partial \Pi }{\partial p}\theta ^{\prime } &=&\alpha ^{\prime } \\ |
1148 |
\frac{D\theta }{Dt} &=&\frac{\mathcal{Q}}{\Pi } \label{eq:atmos-prime} |
\frac{D\theta }{Dt} &=&\frac{\mathcal{Q}}{\Pi } \label{eq:atmos-prime} |
1159 |
HPE's for the ocean written in z-coordinates are obtained. The |
HPE's for the ocean written in z-coordinates are obtained. The |
1160 |
non-Boussinesq equations for oceanic motion are: |
non-Boussinesq equations for oceanic motion are: |
1161 |
\begin{eqnarray} |
\begin{eqnarray} |
1162 |
\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}} |
1163 |
_{h}+\frac{1}{\rho }\mathbf{\nabla }_{z}p &=&\vec{\mathbf{\mathcal{F}}} \\ |
_{h}+\frac{1}{\rho }\mathbf{\nabla }_{z}p &=&\vec{\mathbf{\mathcal{F}}} \\ |
1164 |
\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} |
1165 |
&=&\epsilon _{nh}\mathcal{F}_{w} \\ |
&=&\epsilon _{nh}\mathcal{F}_{w} \\ |
1166 |
\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}} |
1167 |
_{h}+\frac{\partial w}{\partial z} &=&0 \\ |
_{h}+\frac{\partial w}{\partial z} &=&0 \\ |
1168 |
\rho &=&\rho (\theta ,S,p) \\ |
\rho &=&\rho (\theta ,S,p) \\ |
1169 |
\frac{D\theta }{Dt} &=&\mathcal{Q}_{\theta } \\ |
\frac{D\theta }{Dt} &=&\mathcal{Q}_{\theta } \\ |
1170 |
\frac{DS}{Dt} &=&\mathcal{Q}_{s} \label{eq:non-boussinesq} |
\frac{DS}{Dt} &=&\mathcal{Q}_{s} \label{eq:non-boussinesq} |
1171 |
\end{eqnarray}% |
\end{eqnarray} |
1172 |
These equations permit acoustics modes, inertia-gravity waves, |
These equations permit acoustics modes, inertia-gravity waves, |
1173 |
non-hydrostatic motions, a geostrophic (Rossby) mode and a thermo-haline |
non-hydrostatic motions, a geostrophic (Rossby) mode and a thermo-haline |
1174 |
mode. As written, they cannot be integrated forward consistently - if we |
mode. As written, they cannot be integrated forward consistently - if we |
1175 |
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 |
1176 |
consistent with that obtained by stepping (\ref{eq-zns-heat}) and (\ref% |
consistent with that obtained by stepping (\ref{eq-zns-heat}) and (\ref |
1177 |
{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 |
1178 |
therefore necessary to manipulate the system as follows. Differentiating the |
therefore necessary to manipulate the system as follows. Differentiating the |
1179 |
EOS (equation of state) gives: |
EOS (equation of state) gives: |
1186 |
\end{equation} |
\end{equation} |
1187 |
|
|
1188 |
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 |
1189 |
reciprocal of the sound speed ($c_{s}$) squared. Substituting into \ref% |
reciprocal of the sound speed ($c_{s}$) squared. Substituting into \ref |
1190 |
{eq-zns-cont} gives: |
{eq-zns-cont} gives: |
1191 |
\begin{equation} |
\begin{equation} |
1192 |
\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{ |
1193 |
v}}+\partial _{z}w\approx 0 \label{eq-zns-pressure} |
v}}+\partial _{z}w\approx 0 \label{eq-zns-pressure} |
1194 |
\end{equation} |
\end{equation} |
1195 |
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 |
1197 |
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 |
1198 |
can be explicitly integrated forward: |
can be explicitly integrated forward: |
1199 |
\begin{eqnarray} |
\begin{eqnarray} |
1200 |
\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}} |
1201 |
_{h}+\frac{1}{\rho }\mathbf{\nabla }_{z}p &=&\vec{\mathbf{\mathcal{F}}} |
_{h}+\frac{1}{\rho }\mathbf{\nabla }_{z}p &=&\vec{\mathbf{\mathcal{F}}} |
1202 |
\label{eq-cns-hmom} \\ |
\label{eq-cns-hmom} \\ |
1203 |
\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} |
1204 |
&=&\epsilon _{nh}\mathcal{F}_{w} \label{eq-cns-hydro} \\ |
&=&\epsilon _{nh}\mathcal{F}_{w} \label{eq-cns-hydro} \\ |
1205 |
\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{ |
1206 |
v}}_{h}+\frac{\partial w}{\partial z} &=&0 \label{eq-cns-cont} \\ |
v}}_{h}+\frac{\partial w}{\partial z} &=&0 \label{eq-cns-cont} \\ |
1207 |
\rho &=&\rho (\theta ,S,p) \label{eq-cns-eos} \\ |
\rho &=&\rho (\theta ,S,p) \label{eq-cns-eos} \\ |
1208 |
\frac{D\theta }{Dt} &=&\mathcal{Q}_{\theta } \label{eq-cns-heat} \\ |
\frac{D\theta }{Dt} &=&\mathcal{Q}_{\theta } \label{eq-cns-heat} \\ |
1216 |
`Boussinesq assumption'. The only term that then retains the full variation |
`Boussinesq assumption'. The only term that then retains the full variation |
1217 |
in $\rho $ is the gravitational acceleration: |
in $\rho $ is the gravitational acceleration: |
1218 |
\begin{eqnarray} |
\begin{eqnarray} |
1219 |
\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}} |
1220 |
_{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}}} |
1221 |
\label{eq-zcb-hmom} \\ |
\label{eq-zcb-hmom} \\ |
1222 |
\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}} |
1223 |
\frac{\partial p}{\partial z} &=&\epsilon _{nh}\mathcal{F}_{w} |
\frac{\partial p}{\partial z} &=&\epsilon _{nh}\mathcal{F}_{w} |
1224 |
\label{eq-zcb-hydro} \\ |
\label{eq-zcb-hydro} \\ |
1225 |
\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{ |
1226 |
\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} \\ |
1227 |
\rho &=&\rho (\theta ,S,p) \label{eq-zcb-eos} \\ |
\rho &=&\rho (\theta ,S,p) \label{eq-zcb-eos} \\ |
1228 |
\frac{D\theta }{Dt} &=&\mathcal{Q}_{\theta } \label{eq-zcb-heat} \\ |
\frac{D\theta }{Dt} &=&\mathcal{Q}_{\theta } \label{eq-zcb-heat} \\ |
1229 |
\frac{DS}{Dt} &=&\mathcal{Q}_{s} \label{eq-zcb-salt} |
\frac{DS}{Dt} &=&\mathcal{Q}_{s} \label{eq-zcb-salt} |
1230 |
\end{eqnarray} |
\end{eqnarray} |
1231 |
These equations still retain acoustic modes. But, because the |
These equations still retain acoustic modes. But, because the |
1232 |
``compressible'' terms are linearized, the pressure equation \ref% |
``compressible'' terms are linearized, the pressure equation \ref |
1233 |
{eq-zcb-cont} can be integrated implicitly with ease (the time-dependent |
{eq-zcb-cont} can be integrated implicitly with ease (the time-dependent |
1234 |
term appears as a Helmholtz term in the non-hydrostatic pressure equation). |
term appears as a Helmholtz term in the non-hydrostatic pressure equation). |
1235 |
These are the \emph{truly} compressible Boussinesq equations. Note that the |
These are the \emph{truly} compressible Boussinesq equations. Note that the |
1236 |
EOS must have the same pressure dependency as the linearized pressure term, |
EOS must have the same pressure dependency as the linearized pressure term, |
1237 |
ie. $\left. \frac{\partial \rho }{\partial p}\right| _{\theta ,S}=\frac{1}{% |
ie. $\left. \frac{\partial \rho }{\partial p}\right| _{\theta ,S}=\frac{1}{ |
1238 |
c_{s}^{2}}$, for consistency. |
c_{s}^{2}}$, for consistency. |
1239 |
|
|
1240 |
\subsubsection{`Anelastic' z-coordinate equations} |
\subsubsection{`Anelastic' z-coordinate equations} |
1241 |
|
|
1242 |
The anelastic approximation filters the acoustic mode by removing the |
The anelastic approximation filters the acoustic mode by removing the |
1243 |
time-dependency in the continuity (now pressure-) equation (\ref{eq-zcb-cont}% |
time-dependency in the continuity (now pressure-) equation (\ref{eq-zcb-cont} |
1244 |
). This could be done simply by noting that $\frac{Dp}{Dt}\approx -g\rho _{o}% |
). This could be done simply by noting that $\frac{Dp}{Dt}\approx -g\rho _{o} |
1245 |
\frac{Dz}{Dt}=-g\rho _{o}w$, but this leads to an inconsistency between |
\frac{Dz}{Dt}=-g\rho _{o}w$, but this leads to an inconsistency between |
1246 |
continuity and EOS. A better solution is to change the dependency on |
continuity and EOS. A better solution is to change the dependency on |
1247 |
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 |
1252 |
Remembering that the term $\frac{Dp}{Dt}$ in continuity comes from |
Remembering that the term $\frac{Dp}{Dt}$ in continuity comes from |
1253 |
differentiating the EOS, the continuity equation then becomes: |
differentiating the EOS, the continuity equation then becomes: |
1254 |
\begin{equation*} |
\begin{equation*} |
1255 |
\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{ |
1256 |
Dp^{\prime }}{Dt}\right) +\mathbf{\nabla }_{z}\cdot \vec{\mathbf{v}}_{h}+% |
Dp^{\prime }}{Dt}\right) +\mathbf{\nabla }_{z}\cdot \vec{\mathbf{v}}_{h}+ |
1257 |
\frac{\partial w}{\partial z}=0 |
\frac{\partial w}{\partial z}=0 |
1258 |
\end{equation*} |
\end{equation*} |
1259 |
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 |
1260 |
those of acoustic modes, then $\frac{Dp^{\prime }}{Dt}<<(\frac{Dp_{o}}{Dt},% |
those of acoustic modes, then $\frac{Dp^{\prime }}{Dt}<<(\frac{Dp_{o}}{Dt}, |
1261 |
\mathbf{\nabla }\cdot \vec{\mathbf{v}}_{h})$ in the continuity equations and |
\mathbf{\nabla }\cdot \vec{\mathbf{v}}_{h})$ in the continuity equations and |
1262 |
$\left. \frac{\partial \rho }{\partial p}\right| _{\theta ,S}\frac{% |
$\left. \frac{\partial \rho }{\partial p}\right| _{\theta ,S}\frac{ |
1263 |
Dp^{\prime }}{Dt}<<\left. \frac{\partial \rho }{\partial p}\right| _{\theta |
Dp^{\prime }}{Dt}<<\left. \frac{\partial \rho }{\partial p}\right| _{\theta |
1264 |
,S}\frac{Dp_{o}}{Dt}$ in the EOS (\ref{EOSexpansion}). Thus we set $\epsilon |
,S}\frac{Dp_{o}}{Dt}$ in the EOS (\ref{EOSexpansion}). Thus we set $\epsilon |
1265 |
_{s}=0$, removing the dependency on $p^{\prime }$ in the continuity equation |
_{s}=0$, removing the dependency on $p^{\prime }$ in the continuity equation |
1266 |
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 |
1267 |
anelastic continuity equation: |
anelastic continuity equation: |
1268 |
\begin{equation} |
\begin{equation} |
1269 |
\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}- |
1270 |
\frac{g}{c_{s}^{2}}w=0 \label{eq-za-cont1} |
\frac{g}{c_{s}^{2}}w=0 \label{eq-za-cont1} |
1271 |
\end{equation} |
\end{equation} |
1272 |
A slightly different route leads to the quasi-Boussinesq continuity equation |
A slightly different route leads to the quasi-Boussinesq continuity equation |
1273 |
where we use the scaling $\frac{\partial \rho ^{\prime }}{\partial t}+% |
where we use the scaling $\frac{\partial \rho ^{\prime }}{\partial t}+ |
1274 |
\mathbf{\nabla }_{3}\cdot \rho ^{\prime }\vec{\mathbf{v}}<<\mathbf{\nabla }% |
\mathbf{\nabla }_{3}\cdot \rho ^{\prime }\vec{\mathbf{v}}<<\mathbf{\nabla } |
1275 |
_{3}\cdot \rho _{o}\vec{\mathbf{v}}$ yielding: |
_{3}\cdot \rho _{o}\vec{\mathbf{v}}$ yielding: |
1276 |
\begin{equation} |
\begin{equation} |
1277 |
\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{ |
1278 |
\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} |
1279 |
\end{equation} |
\end{equation} |
1280 |
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 |
1283 |
\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}} |
1284 |
\end{equation} |
\end{equation} |
1285 |
Again, note that if $\rho _{o}$ is evaluated from prescribed $\theta _{o}$ |
Again, note that if $\rho _{o}$ is evaluated from prescribed $\theta _{o}$ |
1286 |
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 $\frac{ |
1287 |
g}{c_{s}^{2}}$ in continuity should be referred to those same profiles. The |
g}{c_{s}^{2}}$ in continuity should be referred to those same profiles. The |
1288 |
full set of `quasi-Boussinesq' or `anelastic' equations for the ocean are |
full set of `quasi-Boussinesq' or `anelastic' equations for the ocean are |
1289 |
then: |
then: |
1290 |
\begin{eqnarray} |
\begin{eqnarray} |
1291 |
\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}} |
1292 |
_{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}}} |
1293 |
\label{eq-zab-hmom} \\ |
\label{eq-zab-hmom} \\ |
1294 |
\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}} |
1295 |
\frac{\partial p}{\partial z} &=&\epsilon _{nh}\mathcal{F}_{w} |
\frac{\partial p}{\partial z} &=&\epsilon _{nh}\mathcal{F}_{w} |
1296 |
\label{eq-zab-hydro} \\ |
\label{eq-zab-hydro} \\ |
1297 |
\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{ |
1298 |
\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} \\ |
1299 |
\rho &=&\rho (\theta ,S,p_{o}(z)) \label{eq-zab-eos} \\ |
\rho &=&\rho (\theta ,S,p_{o}(z)) \label{eq-zab-eos} \\ |
1300 |
\frac{D\theta }{Dt} &=&\mathcal{Q}_{\theta } \label{eq-zab-heat} \\ |
\frac{D\theta }{Dt} &=&\mathcal{Q}_{\theta } \label{eq-zab-heat} \\ |
1307 |
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 |
1308 |
yield the ``truly'' incompressible Boussinesq equations: |
yield the ``truly'' incompressible Boussinesq equations: |
1309 |
\begin{eqnarray} |
\begin{eqnarray} |
1310 |
\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}} |
1311 |
_{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}}} |
1312 |
\label{eq-ztb-hmom} \\ |
\label{eq-ztb-hmom} \\ |
1313 |
\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}} |
1314 |
\frac{\partial p}{\partial z} &=&\epsilon _{nh}\mathcal{F}_{w} |
\frac{\partial p}{\partial z} &=&\epsilon _{nh}\mathcal{F}_{w} |
1315 |
\label{eq-ztb-hydro} \\ |
\label{eq-ztb-hydro} \\ |
1316 |
\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} |
1329 |
density thus: |
density thus: |
1330 |
\begin{equation*} |
\begin{equation*} |
1331 |
\rho =\rho _{o}+\rho ^{\prime } |
\rho =\rho _{o}+\rho ^{\prime } |
1332 |
\end{equation*}% |
\end{equation*} |
1333 |
We then assert that variations with depth of $\rho _{o}$ are unimportant |
We then assert that variations with depth of $\rho _{o}$ are unimportant |
1334 |
while the compressible effects in $\rho ^{\prime }$ are: |
while the compressible effects in $\rho ^{\prime }$ are: |
1335 |
\begin{equation*} |
\begin{equation*} |
1336 |
\rho _{o}=\rho _{c} |
\rho _{o}=\rho _{c} |
1337 |
\end{equation*}% |
\end{equation*} |
1338 |
\begin{equation*} |
\begin{equation*} |
1339 |
\rho ^{\prime }=\rho (\theta ,S,p_{o}(z))-\rho _{o} |
\rho ^{\prime }=\rho (\theta ,S,p_{o}(z))-\rho _{o} |
1340 |
\end{equation*}% |
\end{equation*} |
1341 |
This then yields what we can call the semi-compressible Boussinesq |
This then yields what we can call the semi-compressible Boussinesq |
1342 |
equations: |
equations: |
1343 |
\begin{eqnarray} |
\begin{eqnarray} |
1344 |
\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}} |
1345 |
_{h}+\frac{1}{\rho _{c}}\mathbf{\nabla }_{z}p^{\prime } &=&\vec{\mathbf{% |
_{h}+\frac{1}{\rho _{c}}\mathbf{\nabla }_{z}p^{\prime } &=&\vec{\mathbf{ |
1346 |
\mathcal{F}}} \label{eq:ocean-mom} \\ |
\mathcal{F}}} \label{eq:ocean-mom} \\ |
1347 |
\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 |
1348 |
_{c}}\frac{\partial p^{\prime }}{\partial z} &=&\epsilon _{nh}\mathcal{F}_{w} |
_{c}}\frac{\partial p^{\prime }}{\partial z} &=&\epsilon _{nh}\mathcal{F}_{w} |
1353 |
\\ |
\\ |
1354 |
\frac{D\theta }{Dt} &=&\mathcal{Q}_{\theta } \label{eq:ocean-theta} \\ |
\frac{D\theta }{Dt} &=&\mathcal{Q}_{\theta } \label{eq:ocean-theta} \\ |
1355 |
\frac{DS}{Dt} &=&\mathcal{Q}_{s} \label{eq:ocean-salt} |
\frac{DS}{Dt} &=&\mathcal{Q}_{s} \label{eq:ocean-salt} |
1356 |
\end{eqnarray}% |
\end{eqnarray} |
1357 |
Note that the hydrostatic pressure of the resting fluid, including that |
Note that the hydrostatic pressure of the resting fluid, including that |
1358 |
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 |
1359 |
dynamics. |
dynamics. |
1377 |
and vertical direction respectively, are given by (see Fig.2) : |
and vertical direction respectively, are given by (see Fig.2) : |
1378 |
|
|
1379 |
\begin{equation*} |
\begin{equation*} |
1380 |
u=r\cos \phi \frac{D\lambda }{Dt} |
u=r\cos \varphi \frac{D\lambda }{Dt} |
1381 |
\end{equation*} |
\end{equation*} |
1382 |
|
|
1383 |
\begin{equation*} |
\begin{equation*} |
1384 |
v=r\frac{D\phi }{Dt}\qquad |
v=r\frac{D\varphi }{Dt}\qquad |
1385 |
\end{equation*} |
\end{equation*} |
1386 |
$\qquad \qquad \qquad \qquad $ |
$\qquad \qquad \qquad \qquad $ |
1387 |
|
|
1389 |
\dot{r}=\frac{Dr}{Dt} |
\dot{r}=\frac{Dr}{Dt} |
1390 |
\end{equation*} |
\end{equation*} |
1391 |
|
|
1392 |
Here $\phi $ is the latitude, $\lambda $ the longitude, $r$ the radial |
Here $\varphi $ is the latitude, $\lambda $ the longitude, $r$ the radial |
1393 |
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 |
1394 |
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. |
1395 |
|
|
1397 |
spherical coordinates: |
spherical coordinates: |
1398 |
|
|
1399 |
\begin{equation*} |
\begin{equation*} |
1400 |
\nabla \equiv \left( \frac{1}{r\cos \phi }\frac{\partial }{\partial \lambda }% |
\nabla \equiv \left( \frac{1}{r\cos \varphi }\frac{\partial }{\partial \lambda } |
1401 |
,\frac{1}{r}\frac{\partial }{\partial \phi },\frac{\partial }{\partial r}% |
,\frac{1}{r}\frac{\partial }{\partial \varphi },\frac{\partial }{\partial r} |
1402 |
\right) |
\right) |
1403 |
\end{equation*} |
\end{equation*} |
1404 |
|
|
1405 |
\begin{equation*} |
\begin{equation*} |
1406 |
\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 |
1407 |
\lambda }+\frac{\partial }{\partial \phi }\left( v\cos \phi \right) \right\} |
\lambda }+\frac{\partial }{\partial \varphi }\left( v\cos \varphi \right) \right\} |
1408 |
+\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} |
1409 |
\end{equation*} |
\end{equation*} |
1410 |
|
|
1411 |
%%%% \end{document} |
%tci%\end{document} |