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% $Header: /u/gcmpack/manual/part6/generic_advdiff.tex,v 1.6 2005/08/01 18:07:24 cnh Exp $ |
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% $Name: $ |
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\subsection{Generic Advection/Diffusion} |
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\label{sec:pkg:gad} |
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\begin{rawhtml} |
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<!-- CMIREDIR:package_gad: --> |
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\end{rawhtml} |
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The {\tt generic\_advdiff} package contains high-level |
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subroutines to solve the advection-diffusion equation |
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of any tracer, either active (potential temperature, |
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salinity or water vapor) or passive (see pkg/ptracers). |
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(see also sections \ref{sect:tracer_equations} to |
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\ref{sect:tracer_advection_schemes}). |
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\subsubsection{Introduction} |
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Package ``generic\_advdiff'' provides a common set of routines for |
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calculating advective/diffusive fluxes for tracers (cell centered |
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quantities on a C-grid). |
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Many different advection schemes are available: the standard centered |
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second order, centered fourth order and upwind biased third order |
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schemes are known as linear methods and require some stable |
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time-stepping method such as Adams-Bashforth. Alternatives such as |
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flux-limited schemes are stable in the forward sense and are best |
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combined with the multi-dimensional method provided in gad\_advection. |
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\subsubsection{Key subroutines, parameters and files} |
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\label{sec:pkg:gad:implementation_synopsis} |
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There are two high-level routines: |
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\begin{itemize} |
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\item{GAD\_CALC\_RHS} calculates all fluxes at time level ``n'' and is |
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used for the standard linear schemes. This must be used in |
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conjuction with Adams--Bashforth time stepping. Diffusive and |
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parameterized fluxes are always calculated here. |
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\item{GAD\_ADVECTION} calculates just the advective fluxes using the |
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non-linear schemes and can not be used in conjuction with |
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Adams--Bashforth time stepping. |
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\end{itemize} |
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\subsubsection{GAD Diagnostics} |
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\label{sec:pkg:gad:diagnostics} |
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\begin{verbatim} |
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------------------------------------------------------------------------ |
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<-Name->|Levs|<-parsing code->|<-- Units -->|<- Tile (max=80c) |
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------------------------------------------------------------------------ |
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ADVr_TH | 15 |WM LR |degC.m^3/s |Vertical Advective Flux of Pot.Temperature |
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ADVx_TH | 15 |UU 087MR |degC.m^3/s |Zonal Advective Flux of Pot.Temperature |
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ADVy_TH | 15 |VV 086MR |degC.m^3/s |Meridional Advective Flux of Pot.Temperature |
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DFrE_TH | 15 |WM LR |degC.m^3/s |Vertical Diffusive Flux of Pot.Temperature (Explicit part) |
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DIFx_TH | 15 |UU 090MR |degC.m^3/s |Zonal Diffusive Flux of Pot.Temperature |
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DIFy_TH | 15 |VV 089MR |degC.m^3/s |Meridional Diffusive Flux of Pot.Temperature |
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DFrI_TH | 15 |WM LR |degC.m^3/s |Vertical Diffusive Flux of Pot.Temperature (Implicit part) |
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ADVr_SLT| 15 |WM LR |psu.m^3/s |Vertical Advective Flux of Salinity |
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ADVx_SLT| 15 |UU 094MR |psu.m^3/s |Zonal Advective Flux of Salinity |
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ADVy_SLT| 15 |VV 093MR |psu.m^3/s |Meridional Advective Flux of Salinity |
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DFrE_SLT| 15 |WM LR |psu.m^3/s |Vertical Diffusive Flux of Salinity (Explicit part) |
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DIFx_SLT| 15 |UU 097MR |psu.m^3/s |Zonal Diffusive Flux of Salinity |
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DIFy_SLT| 15 |VV 096MR |psu.m^3/s |Meridional Diffusive Flux of Salinity |
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DFrI_SLT| 15 |WM LR |psu.m^3/s |Vertical Diffusive Flux of Salinity (Implicit part) |
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\end{verbatim} |
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