s_phys_pkgs/text/generic_advdiff.tex

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% $Name:  $


\subsection{Generic Advection/Diffusion}
\label{sec:pkg:gad}
\begin{rawhtml}
<!-- CMIREDIR:package_gad: -->
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The {\tt generic\_advdiff} package contains high-level
subroutines to solve the advection-diffusion equation
of any tracer, either active (potential temperature,
salinity or water vapor) or passive (see pkg/ptracers).
(see also sections \ref{sect:tracer_equations} to
\ref{sect:tracer_advection_schemes}).


\subsubsection{Introduction}
Package ``generic\_advdiff'' provides a common set of routines for
calculating advective/diffusive fluxes for tracers (cell centered
quantities on a C-grid).

Many different advection schemes are available: the standard centered
second order, centered fourth order and upwind biased third order
schemes are known as linear methods and require some stable
time-stepping method such as Adams-Bashforth. Alternatives such as
flux-limited schemes are stable in the forward sense and are best
combined with the multi-dimensional method provided in gad\_advection.

\subsubsection{Key subroutines, parameters and files}
\label{sec:pkg:gad:implementation_synopsis}
There are two high-level routines:
\begin{itemize}
\item{GAD\_CALC\_RHS} calculates all fluxes at time level ``n'' and is
  used for the standard linear schemes. This must be used in
  conjuction with Adams--Bashforth time stepping. Diffusive and
  parameterized fluxes are always calculated here.

\item{GAD\_ADVECTION} calculates just the advective fluxes using the
  non-linear schemes and can not be used in conjuction with
  Adams--Bashforth time stepping.
\end{itemize}


1	% $Header: /u/gcmpack/manual/part6/generic_advdiff.tex,v 1.5 2005/07/18 20:45:27 molod Exp $
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4
5	\subsection{Generic Advection/Diffusion}
6	\label{sec:pkg:gad}
7	\begin{rawhtml}
8	<!-- CMIREDIR:package_gad: -->
9	\end{rawhtml}
10
11	The {\tt generic\_advdiff} package contains high-level
12	subroutines to solve the advection-diffusion equation
13	of any tracer, either active (potential temperature,
14	salinity or water vapor) or passive (see pkg/ptracers).
15	(see also sections \ref{sect:tracer_equations} to
16	\ref{sect:tracer_advection_schemes}).
17
18
19	\subsubsection{Introduction}
20	Package ``generic\_advdiff'' provides a common set of routines for
21	calculating advective/diffusive fluxes for tracers (cell centered
22	quantities on a C-grid).
23
24	Many different advection schemes are available: the standard centered
25	second order, centered fourth order and upwind biased third order
26	schemes are known as linear methods and require some stable
27	time-stepping method such as Adams-Bashforth. Alternatives such as
28	flux-limited schemes are stable in the forward sense and are best
29	combined with the multi-dimensional method provided in gad\_advection.
30
31	\subsubsection{Key subroutines, parameters and files}
32	\label{sec:pkg:gad:implementation_synopsis}
33	There are two high-level routines:
34	\begin{itemize}
35	\item{GAD\_CALC\_RHS} calculates all fluxes at time level ``n'' and is
36	used for the standard linear schemes. This must be used in
37	conjuction with Adams--Bashforth time stepping. Diffusive and
38	parameterized fluxes are always calculated here.
39
40	\item{GAD\_ADVECTION} calculates just the advective fluxes using the
41	non-linear schemes and can not be used in conjuction with
42	Adams--Bashforth time stepping.
43	\end{itemize}
44
45
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