Changeset 11123 for NEMO/trunk/doc/latex/NEMO/subfiles/chap_time_domain.tex
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- 2019-06-17T14:22:27+02:00 (5 years ago)
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NEMO/trunk/doc/latex/NEMO/subfiles/chap_time_domain.tex
r10501 r11123 64 64 65 65 The time stepping used for processes other than diffusion is the well-known leapfrog scheme 66 \citep{ Mesinger_Arakawa_Bk76}.66 \citep{mesinger.arakawa_bk76}. 67 67 This scheme is widely used for advection processes in low-viscosity fluids. 68 68 It is a time centred scheme, \ie the RHS in \autoref{eq:STP} is evaluated at time step $t$, the now time step. … … 80 80 To prevent it, the leapfrog scheme is often used in association with a Robert-Asselin time filter 81 81 (hereafter the LF-RA scheme). 82 This filter, first designed by \citet{ Robert_JMSJ66} and more comprehensively studied by \citet{Asselin_MWR72},82 This filter, first designed by \citet{robert_JMSJ66} and more comprehensively studied by \citet{asselin_MWR72}, 83 83 is a kind of laplacian diffusion in time that mixes odd and even time steps: 84 84 \begin{equation} … … 89 89 $\gamma$ is initialized as \np{rn\_atfp} (namelist parameter). 90 90 Its default value is \np{rn\_atfp}~\forcode{= 10.e-3} (see \autoref{sec:STP_mLF}), 91 causing only a weak dissipation of high frequency motions (\citep{ Farge1987}).91 causing only a weak dissipation of high frequency motions (\citep{farge-coulombier_phd87}). 92 92 The addition of a time filter degrades the accuracy of the calculation from second to first order. 93 93 However, the second order truncation error is proportional to $\gamma$, which is small compared to 1. … … 115 115 116 116 This is diffusive in time and conditionally stable. 117 The conditions for stability of second and fourth order horizontal diffusion schemes are \citep{ Griffies_Bk04}:117 The conditions for stability of second and fourth order horizontal diffusion schemes are \citep{griffies_bk04}: 118 118 \begin{equation} 119 119 \label{eq:STP_euler_stability} … … 183 183 $c(k)$ and $d(k)$ are positive and the diagonal term is greater than the sum of the two extra-diagonal terms, 184 184 therefore a special adaptation of the Gauss elimination procedure is used to find the solution 185 (see for example \citet{ Richtmyer1967}).185 (see for example \citet{richtmyer.morton_bk67}). 186 186 187 187 % ------------------------------------------------------------------------------------------------------------- … … 200 200 \caption{ 201 201 \protect\label{fig:TimeStep_flowchart} 202 Sketch of the leapfrog time stepping sequence in \NEMO from \citet{ Leclair_Madec_OM09}.202 Sketch of the leapfrog time stepping sequence in \NEMO from \citet{leclair.madec_OM09}. 203 203 The use of a semi -implicit computation of the hydrostatic pressure gradient requires the tracer equation to 204 204 be stepped forward prior to the momentum equation. … … 219 219 \label{sec:STP_mLF} 220 220 221 Significant changes have been introduced by \cite{ Leclair_Madec_OM09} in the LF-RA scheme in order to221 Significant changes have been introduced by \cite{leclair.madec_OM09} in the LF-RA scheme in order to 222 222 ensure tracer conservation and to allow the use of a much smaller value of the Asselin filter parameter. 223 223 The modifications affect both the forcing and filtering treatments in the LF-RA scheme. … … 237 237 The change in the forcing formulation given by \autoref{eq:STP_forcing} (see \autoref{fig:MLF_forcing}) 238 238 has a significant effect: 239 the forcing term no longer excites the divergence of odd and even time steps \citep{ Leclair_Madec_OM09}.239 the forcing term no longer excites the divergence of odd and even time steps \citep{leclair.madec_OM09}. 240 240 % forcing seen by the model.... 241 241 This property improves the LF-RA scheme in two respects. … … 245 245 (last term in \autoref{eq:STP_RA} compared to \autoref{eq:STP_asselin}). 246 246 Since the filtering of the forcing was the source of non-conservation in the classical LF-RA scheme, 247 the modified formulation becomes conservative \citep{ Leclair_Madec_OM09}.247 the modified formulation becomes conservative \citep{leclair.madec_OM09}. 248 248 Second, the LF-RA becomes a truly quasi -second order scheme. 249 249 Indeed, \autoref{eq:STP_forcing} used in combination with a careful treatment of static instability
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