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\section{Vector invariant momentum equations} |
\section{Vector invariant momentum equations} |
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\label{sect:vect-inv_momentum_equations} |
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The finite volume method lends itself to describing the continuity and |
The finite volume method lends itself to describing the continuity and |
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tracer equations in curvilinear coordinate systems but the appearance |
tracer equations in curvilinear coordinate systems. However, in |
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of new metric terms in the flux-form momentum equations makes |
curvilinear coordinates many new metric terms appear in the momentum |
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generalizing them far from elegant. The vector invariant form of the |
equations (written in Lagrangian or flux-form) making generalization |
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momentum equations are exactly that; invariant under coordinate |
far from elegant. Fortunately, an alternative form of the equations, |
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transformations. |
the vector invariant equations are exactly that; invariant under |
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coordinate transformations so that they can be applied uniformly in |
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any orthogonal curvilinear coordinate system such as spherical |
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coordinates, boundary following or the conformal spherical cube |
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system. |
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The non-hydrostatic vector invariant equations read: |
The non-hydrostatic vector invariant equations read: |
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\begin{equation} |
\begin{equation} |
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The vertical component of relative vorticity is explicitly calculated |
The vertical component of relative vorticity is explicitly calculated |
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and use in the discretization. The particular form is crucial for |
and use in the discretization. The particular form is crucial for |
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numerical stablility; alternative definitions break the conservation |
numerical stability; alternative definitions break the conservation |
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properties of the discrete equations. |
properties of the discrete equations. |
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Relative vorticity is defined: |
Relative vorticity is defined: |
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\end{eqnarray} |
\end{eqnarray} |
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\marginpar{Run-time control needs to be added for these options} The |
\marginpar{Run-time control needs to be added for these options} The |
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disctinction between using absolute vorticity or relative vorticity is |
distinction between using absolute vorticity or relative vorticity is |
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useful when constructing higher order advection schemes; monotone |
useful when constructing higher order advection schemes; monotone |
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advection of relative vorticity behaves differently to monotone |
advection of relative vorticity behaves differently to monotone |
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advection of absolute vorticity. Currently the choice of |
advection of absolute vorticity. Currently the choice of |