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% $Header: /u/gcmpack/manual/part6/seaice.tex,v 1.6 2008/01/15 23:58:53 heimbach Exp $ |
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% $Name: $ |
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%%EH3 Copied from "MITgcm/pkg/seaice/seaice_description.tex" |
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%%EH3 which was written by Dimitris M. |
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\subsection{SEAICE Package} |
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\label{sec:pkg:seaice} |
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\begin{rawhtml} |
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<!-- CMIREDIR:package_seaice: --> |
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\end{rawhtml} |
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|
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Authors: Martin Losch, Dimitris Menemenlis, An Nguyen, Jean-Michel Campin, |
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Patrick Heimbach, Chris Hill and Jinlun Zhang |
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|
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%---------------------------------------------------------------------- |
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\subsubsection{Introduction |
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\label{sec:pkg:exf:intro}} |
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|
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|
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Package ``seaice'' provides a dynamic and thermodynamic interactive |
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sea-ice model. |
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|
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CPP options enable or disable different aspects of the package |
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(Section \ref{sec:pkg:seaice:config}). |
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Runtime options, flags, filenames and field-related dates/times are |
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set in \texttt{data.seaice} |
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(Section \ref{sec:pkg:seaice:runtime}). |
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A description of key subroutines is given in Section |
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\ref{sec:pkg:seaice:subroutines}. |
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Input fields, units and sign conventions are summarized in |
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Section \ref{sec:pkg:seaice:fields_units}, and available diagnostics |
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output is listed in Section \ref{sec:pkg:seaice:fields_diagnostics}. |
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|
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%---------------------------------------------------------------------- |
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|
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\subsubsection{SEAICE configuration, compiling \& running} |
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|
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\paragraph{Compile-time options |
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\label{sec:pkg:seaice:config}} |
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~ |
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|
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As with all MITgcm packages, SEAICE can be turned on or off at compile time |
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% |
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\begin{itemize} |
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% |
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\item |
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using the \texttt{packages.conf} file by adding \texttt{seaice} to it, |
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% |
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\item |
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or using \texttt{genmake2} adding |
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\texttt{-enable=seaice} or \texttt{-disable=seaice} switches |
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% |
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\item |
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\textit{required packages and CPP options}: \\ |
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SEAICE requires the external forcing package \texttt{exf} to be enabled; |
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no additional CPP options are required. |
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% |
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\end{itemize} |
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(see Section \ref{sect:buildingCode}). |
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|
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Parts of the SEAICE code can be enabled or disabled at compile time |
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via CPP preprocessor flags. These options are set in either |
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\texttt{SEAICE\_OPTIONS.h} or in \texttt{ECCO\_CPPOPTIONS.h}. |
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Table \ref{tab:pkg:seaice:cpp} summarizes these options. |
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|
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\begin{table}[h!] |
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\centering |
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\label{tab:pkg:seaice:cpp} |
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{\footnotesize |
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\begin{tabular}{|l|l|} |
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\hline |
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\textbf{CPP option} & \textbf{Description} \\ |
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\hline \hline |
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\texttt{SEAICE\_DEBUG} & |
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Enhance STDOUT for debugging \\ |
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\texttt{SEAICE\_ALLOW\_DYNAMICS} & |
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sea-ice dynamics code \\ |
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\texttt{SEAICE\_CGRID} & |
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LSR solver on C-grid (rather than original B-grid \\ |
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\texttt{SEAICE\_ALLOW\_EVP} & |
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use EVP rather than LSR rheology solver \\ |
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\texttt{SEAICE\_EXTERNAL\_FLUXES} & |
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use EXF-computed fluxes as starting point \\ |
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\texttt{SEAICE\_MULTICATEGORY} & |
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enable 8-category thermodynamics \\ |
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\texttt{SEAICE\_VARIABLE\_FREEZING\_POINT} & |
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enable linear dependence of the freezing point on salinity \\ |
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\texttt{ALLOW\_SEAICE\_FLOODING} & |
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enable snow to ice conversion for submerged sea-ice \\ |
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\texttt{SEAICE\_SALINITY} & |
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enable "salty" sea-ice \\ |
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\texttt{SEAICE\_CAP\_HEFF} & |
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enable capping of sea-ice thickness to MAX\_HEFF \\ |
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\hline |
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\end{tabular} |
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} |
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\caption{~} |
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\end{table} |
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|
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%---------------------------------------------------------------------- |
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|
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\subsubsection{Run-time parameters |
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\label{sec:pkg:seaice:runtime}} |
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|
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Run-time parameters are set in files |
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\texttt{data.pkg} (read in \texttt{packages\_readparms.F}), |
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and \texttt{data.seaice} (read in \texttt{seaice\_readparms.F}). |
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|
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\paragraph{Enabling the package} |
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~ \\ |
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% |
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A package is switched on/off at runtime by setting |
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(e.g. for SEAICE) \texttt{useSEAICE = .TRUE.} in \texttt{data.pkg}. |
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|
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\paragraph{General flags and parameters} |
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~ \\ |
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% |
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\input{part6/seaice-parms.tex} |
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|
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|
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%---------------------------------------------------------------------- |
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\subsubsection{Description |
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\label{sec:pkg:seaice:descr}} |
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[TO BE CONTINUED/MODIFIED] |
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|
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Sea-ice model thermodynamics are based on Hibler |
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\cite{hib80}, that is, a 2-category model that simulates ice thickness |
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and concentration. Snow is simulated as per Zhang et al. |
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\cite{zha98a}. Although recent years have seen an increased use of |
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multi-category thickness distribution sea-ice models for climate |
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studies, the Hibler 2-category ice model is still the most widely used |
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model and has resulted in realistic simulation of sea-ice variability |
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on regional and global scales. Being less complicated, compared to |
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multi-category models, the 2-category model permits easier application |
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of adjoint model optimization methods. |
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|
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Note, however, that the Hibler 2-category model and its variants use a |
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so-called zero-layer thermodynamic model to estimate ice growth and |
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decay. The zero-layer thermodynamic model assumes that ice does not |
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store heat and, therefore, tends to exaggerate the seasonal |
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variability in ice thickness. This exaggeration can be significantly |
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reduced by using Semtner's \cite{sem76} three-layer thermodynamic |
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model that permits heat storage in ice. Recently, the three-layer |
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thermodynamic model has been reformulated by Winton \cite{win00}. The |
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reformulation improves model physics by representing the brine content |
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of the upper ice with a variable heat capacity. It also improves |
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model numerics and consumes less computer time and memory. The Winton |
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sea-ice thermodynamics have been ported to the MIT GCM; they currently |
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reside under pkg/thsice. At present pkg/thsice is not fully |
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compatible with pkg/seaice and with pkg/exf. But the eventual |
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objective is to have fully compatible and interchangeable |
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thermodynamic packages for sea-ice, so that it becomes possible to use |
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Hibler dynamics with Winton thermodyanmics. |
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|
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The ice dynamics models that are most widely used for large-scale |
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climate studies are the viscous-plastic (VP) model \cite{hib79}, the |
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cavitating fluid (CF) model \cite{fla92}, and the |
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elastic-viscous-plastic (EVP) model \cite{hun97}. Compared to the VP |
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model, the CF model does not allow ice shear in calculating ice |
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motion, stress, and deformation. EVP models approximate VP by adding |
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an elastic term to the equations for easier adaptation to parallel |
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computers. Because of its higher accuracy in plastic solution and |
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relatively simpler formulation, compared to the EVP model, we decided |
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to use the VP model as the dynamic component of our ice model. To do |
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this we extended the alternating-direction-implicit (ADI) method of |
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Zhang and Rothrock \cite{zha00} for use in a parallel configuration. |
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|
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The sea ice model requires the following input fields: 10-m winds, 2-m |
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air temperature and specific humidity, downward longwave and shortwave |
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radiations, precipitation, evaporation, and river and glacier runoff. |
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The sea ice model also requires surface temperature from the ocean |
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model and third level horizontal velocity which is used as a proxy for |
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surface geostrophic velocity. Output fields are surface wind stress, |
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evaporation minus precipitation minus runoff, net surface heat flux, |
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and net shortwave flux. The sea-ice model is global: in ice-free |
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regions bulk formulae are used to estimate oceanic forcing from the |
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atmospheric fields. |
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|
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|
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%---------------------------------------------------------------------- |
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|
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\subsubsection{Key subroutines |
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\label{sec:pkg:seaice:subroutines}} |
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|
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Top-level routine: \texttt{exf\_getforcing.F} |
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{\footnotesize |
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\begin{verbatim} |
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|
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C !CALLING SEQUENCE: |
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c ... |
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c seaice_model (TOP LEVEL ROUTINE) |
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c | |
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c |-- #ifdef SEAICE_CGRID |
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c | SEAICE_DYNSOLVER |
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c | | |
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c | |-- < compute proxy for geostrophic velocity > |
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c | | |
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c | |-- < set up mass per unit area and Coriolis terms > |
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c | | |
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c | |-- < dynamic masking of areas with no ice > |
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c | | |
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c | | |
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|
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c | #ELSE |
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c | DYNSOLVER |
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c | #ENDIF |
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c | |
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c |-- if ( useOBCS ) |
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c | OBCS_APPLY_UVICE |
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c | |
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c |-- if ( SEAICEadvHeff .OR. SEAICEadvArea .OR. SEAICEadvSnow .OR. SEAICEadvSalt ) |
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c | SEAICE_ADVDIFF |
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c | |
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c |-- if ( usePW79thermodynamics ) |
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c | SEAICE_GROWTH |
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c | |
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c |-- if ( useOBCS ) |
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c | if ( SEAICEadvHeff ) OBCS_APPLY_HEFF |
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c | if ( SEAICEadvArea ) OBCS_APPLY_AREA |
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c | if ( SEAICEadvSALT ) OBCS_APPLY_HSALT |
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c | if ( SEAICEadvSNOW ) OBCS_APPLY_HSNOW |
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c | |
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c |-- < do various exchanges > |
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c | |
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c |-- < do additional diagnostics > |
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c | |
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c o |
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|
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\end{verbatim} |
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} |
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|
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|
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%---------------------------------------------------------------------- |
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|
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\subsubsection{EXF diagnostics |
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\label{sec:pkg:seaice:diagnostics}} |
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|
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Diagnostics output is available via the diagnostics package |
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(see Section \ref{sec:pkg:diagnostics}). |
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Available output fields are summarized in |
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Table \ref{tab:pkg:seaice:diagnostics}. |
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|
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\begin{table}[h!] |
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\centering |
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\label{tab:pkg:seaice:diagnostics} |
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{\footnotesize |
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\begin{verbatim} |
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---------+----+----+----------------+----------------- |
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<-Name->|Levs|grid|<-- Units -->|<- Tile (max=80c) |
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---------+----+----+----------------+----------------- |
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SIarea | 1 |SM |m^2/m^2 |SEAICE fractional ice-covered area [0 to 1] |
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SIheff | 1 |SM |m |SEAICE effective ice thickness |
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SIuice | 1 |UU |m/s |SEAICE zonal ice velocity, >0 from West to East |
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SIvice | 1 |VV |m/s |SEAICE merid. ice velocity, >0 from South to North |
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SIhsnow | 1 |SM |m |SEAICE snow thickness |
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SIhsalt | 1 |SM |g/m^2 |SEAICE effective salinity |
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SIatmFW | 1 |SM |m/s |Net freshwater flux from the atmosphere (+=down) |
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SIuwind | 1 |SM |m/s |SEAICE zonal 10-m wind speed, >0 increases uVel |
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SIvwind | 1 |SM |m/s |SEAICE meridional 10-m wind speed, >0 increases uVel |
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SIfu | 1 |UU |N/m^2 |SEAICE zonal surface wind stress, >0 increases uVel |
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SIfv | 1 |VV |N/m^2 |SEAICE merid. surface wind stress, >0 increases vVel |
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SIempmr | 1 |SM |m/s |SEAICE upward freshwater flux, > 0 increases salt |
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SIqnet | 1 |SM |W/m^2 |SEAICE upward heatflux, turb+rad, >0 decreases theta |
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SIqsw | 1 |SM |W/m^2 |SEAICE upward shortwave radiat., >0 decreases theta |
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SIpress | 1 |SM |m^2/s^2 |SEAICE strength (with upper and lower limit) |
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SIzeta | 1 |SM |m^2/s |SEAICE nonlinear bulk viscosity |
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SIeta | 1 |SM |m^2/s |SEAICE nonlinear shear viscosity |
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SIsigI | 1 |SM |no units |SEAICE normalized principle stress, component one |
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SIsigII | 1 |SM |no units |SEAICE normalized principle stress, component two |
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SIthdgrh| 1 |SM |m/s |SEAICE thermodynamic growth rate of effective ice thickness |
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SIsnwice| 1 |SM |m/s |SEAICE ice formation rate due to flooding |
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SIuheff | 1 |UU |m^2/s |Zonal Transport of effective ice thickness |
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SIvheff | 1 |VV |m^2/s |Meridional Transport of effective ice thickness |
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ADVxHEFF| 1 |UU |m.m^2/s |Zonal Advective Flux of eff ice thickn |
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ADVyHEFF| 1 |VV |m.m^2/s |Meridional Advective Flux of eff ice thickn |
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DFxEHEFF| 1 |UU |m.m^2/s |Zonal Diffusive Flux of eff ice thickn |
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DFyEHEFF| 1 |VV |m.m^2/s |Meridional Diffusive Flux of eff ice thickn |
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ADVxAREA| 1 |UU |m^2/m^2.m^2/s |Zonal Advective Flux of fract area |
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ADVyAREA| 1 |VV |m^2/m^2.m^2/s |Meridional Advective Flux of fract area |
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DFxEAREA| 1 |UU |m^2/m^2.m^2/s |Zonal Diffusive Flux of fract area |
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DFyEAREA| 1 |VV |m^2/m^2.m^2/s |Meridional Diffusive Flux of fract area |
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ADVxSNOW| 1 |UU |m.m^2/s |Zonal Advective Flux of eff snow thickn |
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ADVySNOW| 1 |VV |m.m^2/s |Meridional Advective Flux of eff snow thickn |
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DFxESNOW| 1 |UU |m.m^2/s |Zonal Diffusive Flux of eff snow thickn |
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DFyESNOW| 1 |VV |m.m^2/s |Meridional Diffusive Flux of eff snow thickn |
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ADVxSSLT| 1 |UU |psu.m^2/s |Zonal Advective Flux of seaice salinity |
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ADVySSLT| 1 |VV |psu.m^2/s |Meridional Advective Flux of seaice salinity |
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DFxESSLT| 1 |UU |psu.m^2/s |Zonal Diffusive Flux of seaice salinity |
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DFyESSLT| 1 |VV |psu.m^2/s |Meridional Diffusive Flux of seaice salinity |
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\end{verbatim} |
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} |
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\caption{~} |
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\end{table} |
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|
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|
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%\subsubsection{Package Reference} |
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|
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\subsubsection{Experiments and tutorials that use seaice} |
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\label{sec:pkg:seaice:experiments} |
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|
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\begin{itemize} |
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\item{Labrador Sea experiment in lab\_sea verification directory. } |
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\end{itemize} |
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