Changeset 781 for trunk/DOC/BETA/Chapters/Chap_DOM.tex
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 20080103T12:10:08+01:00 (13 years ago)
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trunk/DOC/BETA/Chapters/Chap_DOM.tex
r707 r781 316 316 the ocean. This is unnecessary when the ocean is forced by fixed atmospheric 317 317 conditions. A possibility is offered to the user to set to zero the 318 bathymetry in rectangular regions covering those closed seas (see \S\ref{MISC_closea}) 318 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. 319 319 320 320 %  … … 515 515 516 516 In case of rigidlid 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 517 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}).517 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}). 518 518 519 519 From the \textit{mbathy} array, the mask fields are defined as follows: … … 553 553 well as the implication in term of starting or restarting a model 554 554 simulation. Note that the time stepping is generally performed in a one step 555 operation :it would be dangerous to let a prognostic variable evolve in time for each term successively.555 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. 556 556 557 557 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 timestepping 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 timesplitting options are used. … … 621 621 \end{equation} 622 622 623 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 totime evolution of $x$ between $t_o$ and $t_1$:623 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 $t_1$: 624 624 \begin{equation} \label{Eq_DOM_nxt4} 625 625 \begin{split}
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