Changeset 781 for trunk/DOC/BETA/Chapters/Chap_DOM.tex

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Timestamp:
2008-01-03T12:10:08+01:00 (13 years ago)
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doc update, see ticket:1

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 r707 the ocean. This is unnecessary when the ocean is forced by fixed atmospheric conditions. A possibility is offered to the user to set to zero the bathymetry in rectangular regions covering those closed seas (see \S\ref{MISC_closea}) bathymetry in rectangular regions covering those closed seas (see \S\ref{MISC_closea}), but the code has to be adapted to the user's configuration. % ------------------------------------------------------------------------------------------------------------- In case of rigid-lid approximation and islands in the computational domain (\np{ln\_dynspg\_rl}=true and \key{island} defined), the \textit{mbathy} array must be provided and takes values from $-N$ to \jp{jpk}-1. It provides the following information: $mbathy(i,j) = -n, \ n \in \left] 0,N \right]$, $T-$points are land points of the $n^{th}$ island ; $mbathy(i,j) =0$, $T-$points are land points of the main land (continent) ; $mbathy(i,j) =k$, the first $k$ $T$- and $w$-points are ocean points, the others land points. This is used to compute the island barotropic stream function used in rigid lid computation (see \S\ref{LBC_isl}). following information: $mbathy(i,j) = -n, \ n \in \left] 0,N \right]$, $T-$points are land points of the $n^{th}$ island ; $mbathy(i,j) =0$, $T-$points are land points of the main land (continent) ; $mbathy(i,j) =k$, the first $k$ $T$- and $w$-points are ocean points, the others land points. This is used to compute the island barotropic stream function used in rigid lid computation (see \S\ref{MISC_solisl}). From the \textit{mbathy} array, the mask fields are defined as follows: well as the implication in term of starting or restarting a model simulation. Note that the time stepping is generally performed in a one step operation: it would be dangerous to let a prognostic variable evolve in time for each term successively. operation. With such a complex and nonlinear system of equations it would be dangerous to let a prognostic variable evolve in time for each term successively. The three level scheme requires three arrays for the prognostic variables. For each variable $x$ there is $x_b$ (before) and $x_n$ (now). The third array, although referred to as $x_a$ (after) in the code, is usually not the variable $x_a$ at the next time step; rather, it is used to store the time derivative (RHS in \eqref{Eq_DOM_nxt}) prior to time-stepping the equation. Generally, the time stepping is performed once at each time step in \mdl{tranxt} and \mdl{dynnxt} modules, excepted for implicit vertical diffusion or sea surface height when time-splitting options are used. Equations  \ref{Eq_DOM_nxt2} and \ref{Eq_DOM_nxt3} suggest several remarks. First the Asselin filter is definitively a second order time diffusive operator which is evaluated at centered time step. The magnitude of this diffusion is proportional to the time step (with $\gamma$ usually taken between $10^{-1}$ to $10^{-3}$). Second, this term have to be taken into account in all budget of the equations (mass, heat content, salt content, kinetic energy...). Nevertheless, we stress here that it is small and does not systematic biases. Indeed let evaluates how it contributes to time evolution of $x$ between $t_o$ and $t_1$: Equations  \ref{Eq_DOM_nxt2} and \ref{Eq_DOM_nxt3} suggest several remarks. First the Asselin filter is definitively a second order time diffusive operator which is evaluated at centered time step. The magnitude of this diffusion is proportional to the time step (with $\gamma$ usually taken between $10^{-1}$ to $10^{-3}$) . Second, this term has to be taken into account in all budgets of the equations (mass, heat content, salt content, kinetic energy...). Nevertheless,we stress here that it is small and does not create systematic biases. Indeed let us evaluate how it contributes to the time evolution of $x$ between $t_o$ and $t_1$: \label{Eq_DOM_nxt4} \begin{split}