| 1 |
% $Header: /u/gcmpack/manual/part6/seaice.tex,v 1.5 2006/06/28 15:35:07 molod Exp $ |
| 2 |
% $Name: $ |
| 3 |
|
| 4 |
%%EH3 Copied from "MITgcm/pkg/seaice/seaice_description.tex" |
| 5 |
%%EH3 which was written by Dimitris M. |
| 6 |
|
| 7 |
|
| 8 |
\subsection{SEAICE Package} |
| 9 |
\label{sec:pkg:seaice} |
| 10 |
\begin{rawhtml} |
| 11 |
<!-- CMIREDIR:package_seaice: --> |
| 12 |
\end{rawhtml} |
| 13 |
|
| 14 |
Authors: Martin Losch, Dimitris Menemenlis, An Nguyen, Jean-Michel Campin, |
| 15 |
Patrick Heimbach, Chris Hill and Jinlun Zhang |
| 16 |
|
| 17 |
%---------------------------------------------------------------------- |
| 18 |
\subsubsection{Introduction |
| 19 |
\label{sec:pkg:exf:intro}} |
| 20 |
|
| 21 |
|
| 22 |
Package ``seaice'' provides a dynamic and thermodynamic interactive |
| 23 |
sea-ice model. |
| 24 |
|
| 25 |
CPP options enable or disable different aspects of the package |
| 26 |
(Section \ref{sec:pkg:seaice:config}). |
| 27 |
Runtime options, flags, filenames and field-related dates/times are |
| 28 |
set in \texttt{data.seaice} |
| 29 |
(Section \ref{sec:pkg:seaice:runtime}). |
| 30 |
A description of key subroutines is given in Section |
| 31 |
\ref{sec:pkg:seaice:subroutines}. |
| 32 |
Input fields, units and sign conventions are summarized in |
| 33 |
Section \ref{sec:pkg:seaice:fields_units}, and available diagnostics |
| 34 |
output is listed in Section \ref{sec:pkg:seaice:fields_diagnostics}. |
| 35 |
|
| 36 |
%---------------------------------------------------------------------- |
| 37 |
|
| 38 |
\subsubsection{SEAICE configuration, compiling \& running} |
| 39 |
|
| 40 |
\paragraph{Compile-time options |
| 41 |
\label{sec:pkg:seaice:config}} |
| 42 |
~ |
| 43 |
|
| 44 |
As with all MITgcm packages, SEAICE can be turned on or off at compile time |
| 45 |
% |
| 46 |
\begin{itemize} |
| 47 |
% |
| 48 |
\item |
| 49 |
using the \texttt{packages.conf} file by adding \texttt{seaice} to it, |
| 50 |
% |
| 51 |
\item |
| 52 |
or using \texttt{genmake2} adding |
| 53 |
\texttt{-enable=seaice} or \texttt{-disable=seaice} switches |
| 54 |
% |
| 55 |
\item |
| 56 |
\textit{required packages and CPP options}: \\ |
| 57 |
SEAICE requires the external forcing package \texttt{exf} to be enabled; |
| 58 |
no additional CPP options are required. |
| 59 |
% |
| 60 |
\end{itemize} |
| 61 |
(see Section \ref{sect:buildingCode}). |
| 62 |
|
| 63 |
Parts of the SEAICE code can be enabled or disabled at compile time |
| 64 |
via CPP preprocessor flags. These options are set in either |
| 65 |
\texttt{SEAICE\_OPTIONS.h} or in \texttt{ECCO\_CPPOPTIONS.h}. |
| 66 |
Table \ref{tab:pkg:seaice:cpp} summarizes these options. |
| 67 |
|
| 68 |
\begin{table}[h!] |
| 69 |
\centering |
| 70 |
\label{tab:pkg:seaice:cpp} |
| 71 |
{\footnotesize |
| 72 |
\begin{tabular}{|l|l|} |
| 73 |
\hline |
| 74 |
\textbf{CPP option} & \textbf{Description} \\ |
| 75 |
\hline \hline |
| 76 |
\texttt{SEAICE\_DEBUG} & |
| 77 |
Enhance STDOUT for debugging \\ |
| 78 |
\texttt{SEAICE\_ALLOW\_DYNAMICS} & |
| 79 |
sea-ice dynamics code \\ |
| 80 |
\texttt{SEAICE\_CGRID} & |
| 81 |
LSR solver on C-grid (rather than original B-grid \\ |
| 82 |
\texttt{SEAICE\_ALLOW\_EVP} & |
| 83 |
use EVP rather than LSR rheology solver \\ |
| 84 |
\texttt{SEAICE\_EXTERNAL\_FLUXES} & |
| 85 |
use EXF-computed fluxes as starting point \\ |
| 86 |
\texttt{SEAICE\_MULTICATEGORY} & |
| 87 |
enable 8-category thermodynamics \\ |
| 88 |
\texttt{SEAICE\_VARIABLE\_FREEZING\_POINT} & |
| 89 |
enable linear dependence of the freezing point on salinity \\ |
| 90 |
\texttt{ALLOW\_SEAICE\_FLOODING} & |
| 91 |
enable snow to ice conversion for submerged sea-ice \\ |
| 92 |
\texttt{SEAICE\_SALINITY} & |
| 93 |
enable "salty" sea-ice \\ |
| 94 |
\texttt{SEAICE\_CAP\_HEFF} & |
| 95 |
enable capping of sea-ice thickness to MAX\_HEFF \\ |
| 96 |
\hline |
| 97 |
\end{tabular} |
| 98 |
} |
| 99 |
\caption{~} |
| 100 |
\end{table} |
| 101 |
|
| 102 |
%---------------------------------------------------------------------- |
| 103 |
|
| 104 |
\subsubsection{Run-time parameters |
| 105 |
\label{sec:pkg:seaice:runtime}} |
| 106 |
|
| 107 |
Run-time parameters are set in files |
| 108 |
\texttt{data.pkg} (read in \texttt{packages\_readparms.F}), |
| 109 |
and \texttt{data.seaice} (read in \texttt{seaice\_readparms.F}). |
| 110 |
|
| 111 |
\paragraph{Enabling the package} |
| 112 |
~ \\ |
| 113 |
% |
| 114 |
A package is switched on/off at runtime by setting |
| 115 |
(e.g. for SEAICE) \texttt{useSEAICE = .TRUE.} in \texttt{data.pkg}. |
| 116 |
|
| 117 |
\paragraph{General flags and parameters} |
| 118 |
~ \\ |
| 119 |
% |
| 120 |
\input{part6/seaice-parms.tex} |
| 121 |
|
| 122 |
|
| 123 |
|
| 124 |
%---------------------------------------------------------------------- |
| 125 |
\subsubsection{Description |
| 126 |
\label{sec:pkg:seaice:descr}} |
| 127 |
|
| 128 |
[TO BE CONTINUED/MODIFIED] |
| 129 |
|
| 130 |
Sea-ice model thermodynamics are based on Hibler |
| 131 |
\cite{hib80}, that is, a 2-category model that simulates ice thickness |
| 132 |
and concentration. Snow is simulated as per Zhang et al. |
| 133 |
\cite{zha98a}. Although recent years have seen an increased use of |
| 134 |
multi-category thickness distribution sea-ice models for climate |
| 135 |
studies, the Hibler 2-category ice model is still the most widely used |
| 136 |
model and has resulted in realistic simulation of sea-ice variability |
| 137 |
on regional and global scales. Being less complicated, compared to |
| 138 |
multi-category models, the 2-category model permits easier application |
| 139 |
of adjoint model optimization methods. |
| 140 |
|
| 141 |
Note, however, that the Hibler 2-category model and its variants use a |
| 142 |
so-called zero-layer thermodynamic model to estimate ice growth and |
| 143 |
decay. The zero-layer thermodynamic model assumes that ice does not |
| 144 |
store heat and, therefore, tends to exaggerate the seasonal |
| 145 |
variability in ice thickness. This exaggeration can be significantly |
| 146 |
reduced by using Semtner's \cite{sem76} three-layer thermodynamic |
| 147 |
model that permits heat storage in ice. Recently, the three-layer |
| 148 |
thermodynamic model has been reformulated by Winton \cite{win00}. The |
| 149 |
reformulation improves model physics by representing the brine content |
| 150 |
of the upper ice with a variable heat capacity. It also improves |
| 151 |
model numerics and consumes less computer time and memory. The Winton |
| 152 |
sea-ice thermodynamics have been ported to the MIT GCM; they currently |
| 153 |
reside under pkg/thsice. At present pkg/thsice is not fully |
| 154 |
compatible with pkg/seaice and with pkg/exf. But the eventual |
| 155 |
objective is to have fully compatible and interchangeable |
| 156 |
thermodynamic packages for sea-ice, so that it becomes possible to use |
| 157 |
Hibler dynamics with Winton thermodyanmics. |
| 158 |
|
| 159 |
The ice dynamics models that are most widely used for large-scale |
| 160 |
climate studies are the viscous-plastic (VP) model \cite{hib79}, the |
| 161 |
cavitating fluid (CF) model \cite{fla92}, and the |
| 162 |
elastic-viscous-plastic (EVP) model \cite{hun97}. Compared to the VP |
| 163 |
model, the CF model does not allow ice shear in calculating ice |
| 164 |
motion, stress, and deformation. EVP models approximate VP by adding |
| 165 |
an elastic term to the equations for easier adaptation to parallel |
| 166 |
computers. Because of its higher accuracy in plastic solution and |
| 167 |
relatively simpler formulation, compared to the EVP model, we decided |
| 168 |
to use the VP model as the dynamic component of our ice model. To do |
| 169 |
this we extended the alternating-direction-implicit (ADI) method of |
| 170 |
Zhang and Rothrock \cite{zha00} for use in a parallel configuration. |
| 171 |
|
| 172 |
The sea ice model requires the following input fields: 10-m winds, 2-m |
| 173 |
air temperature and specific humidity, downward longwave and shortwave |
| 174 |
radiations, precipitation, evaporation, and river and glacier runoff. |
| 175 |
The sea ice model also requires surface temperature from the ocean |
| 176 |
model and third level horizontal velocity which is used as a proxy for |
| 177 |
surface geostrophic velocity. Output fields are surface wind stress, |
| 178 |
evaporation minus precipitation minus runoff, net surface heat flux, |
| 179 |
and net shortwave flux. The sea-ice model is global: in ice-free |
| 180 |
regions bulk formulae are used to estimate oceanic forcing from the |
| 181 |
atmospheric fields. |
| 182 |
|
| 183 |
|
| 184 |
%---------------------------------------------------------------------- |
| 185 |
|
| 186 |
\subsubsection{Key subroutines |
| 187 |
\label{sec:pkg:seaice:subroutines}} |
| 188 |
|
| 189 |
Top-level routine: \texttt{exf\_getforcing.F} |
| 190 |
|
| 191 |
{\footnotesize |
| 192 |
\begin{verbatim} |
| 193 |
|
| 194 |
C !CALLING SEQUENCE: |
| 195 |
c ... |
| 196 |
c seaice_model (TOP LEVEL ROUTINE) |
| 197 |
c | |
| 198 |
c |-- #ifdef SEAICE_CGRID |
| 199 |
c | SEAICE_DYNSOLVER |
| 200 |
c | #ELSE |
| 201 |
c | DYNSOLVER |
| 202 |
c | #ENDIF |
| 203 |
c | |
| 204 |
c ... |
| 205 |
|
| 206 |
\end{verbatim} |
| 207 |
} |
| 208 |
|
| 209 |
|
| 210 |
%---------------------------------------------------------------------- |
| 211 |
|
| 212 |
\subsubsection{EXF diagnostics |
| 213 |
\label{sec:pkg:seaice:diagnostics}} |
| 214 |
|
| 215 |
Diagnostics output is available via the diagnostics package |
| 216 |
(see Section \ref{sec:pkg:diagnostics}). |
| 217 |
Available output fields are summarized in |
| 218 |
Table \ref{tab:pkg:seaice:diagnostics}. |
| 219 |
|
| 220 |
\begin{table}[h!] |
| 221 |
\centering |
| 222 |
\label{tab:pkg:seaice:diagnostics} |
| 223 |
{\footnotesize |
| 224 |
\begin{verbatim} |
| 225 |
---------+----+----+----------------+----------------- |
| 226 |
<-Name->|Levs|grid|<-- Units -->|<- Tile (max=80c) |
| 227 |
---------+----+----+----------------+----------------- |
| 228 |
SIarea | 1 |SM |m^2/m^2 |SEAICE fractional ice-covered area [0 to 1] |
| 229 |
SIheff | 1 |SM |m |SEAICE effective ice thickness |
| 230 |
SIuice | 1 |UU |m/s |SEAICE zonal ice velocity, >0 from West to East |
| 231 |
SIvice | 1 |VV |m/s |SEAICE merid. ice velocity, >0 from South to North |
| 232 |
SIhsnow | 1 |SM |m |SEAICE snow thickness |
| 233 |
SIhsalt | 1 |SM |g/m^2 |SEAICE effective salinity |
| 234 |
SIatmFW | 1 |SM |m/s |Net freshwater flux from the atmosphere (+=down) |
| 235 |
SIuwind | 1 |SM |m/s |SEAICE zonal 10-m wind speed, >0 increases uVel |
| 236 |
SIvwind | 1 |SM |m/s |SEAICE meridional 10-m wind speed, >0 increases uVel |
| 237 |
SIfu | 1 |UU |N/m^2 |SEAICE zonal surface wind stress, >0 increases uVel |
| 238 |
SIfv | 1 |VV |N/m^2 |SEAICE merid. surface wind stress, >0 increases vVel |
| 239 |
SIempmr | 1 |SM |m/s |SEAICE upward freshwater flux, > 0 increases salt |
| 240 |
SIqnet | 1 |SM |W/m^2 |SEAICE upward heatflux, turb+rad, >0 decreases theta |
| 241 |
SIqsw | 1 |SM |W/m^2 |SEAICE upward shortwave radiat., >0 decreases theta |
| 242 |
SIpress | 1 |SM |m^2/s^2 |SEAICE strength (with upper and lower limit) |
| 243 |
SIzeta | 1 |SM |m^2/s |SEAICE nonlinear bulk viscosity |
| 244 |
SIeta | 1 |SM |m^2/s |SEAICE nonlinear shear viscosity |
| 245 |
SIsigI | 1 |SM |no units |SEAICE normalized principle stress, component one |
| 246 |
SIsigII | 1 |SM |no units |SEAICE normalized principle stress, component two |
| 247 |
SIthdgrh| 1 |SM |m/s |SEAICE thermodynamic growth rate of effective ice thickness |
| 248 |
SIsnwice| 1 |SM |m/s |SEAICE ice formation rate due to flooding |
| 249 |
SIuheff | 1 |UU |m^2/s |Zonal Transport of effective ice thickness |
| 250 |
SIvheff | 1 |VV |m^2/s |Meridional Transport of effective ice thickness |
| 251 |
ADVxHEFF| 1 |UU |m.m^2/s |Zonal Advective Flux of eff ice thickn |
| 252 |
ADVyHEFF| 1 |VV |m.m^2/s |Meridional Advective Flux of eff ice thickn |
| 253 |
DFxEHEFF| 1 |UU |m.m^2/s |Zonal Diffusive Flux of eff ice thickn |
| 254 |
DFyEHEFF| 1 |VV |m.m^2/s |Meridional Diffusive Flux of eff ice thickn |
| 255 |
ADVxAREA| 1 |UU |m^2/m^2.m^2/s |Zonal Advective Flux of fract area |
| 256 |
ADVyAREA| 1 |VV |m^2/m^2.m^2/s |Meridional Advective Flux of fract area |
| 257 |
DFxEAREA| 1 |UU |m^2/m^2.m^2/s |Zonal Diffusive Flux of fract area |
| 258 |
DFyEAREA| 1 |VV |m^2/m^2.m^2/s |Meridional Diffusive Flux of fract area |
| 259 |
ADVxSNOW| 1 |UU |m.m^2/s |Zonal Advective Flux of eff snow thickn |
| 260 |
ADVySNOW| 1 |VV |m.m^2/s |Meridional Advective Flux of eff snow thickn |
| 261 |
DFxESNOW| 1 |UU |m.m^2/s |Zonal Diffusive Flux of eff snow thickn |
| 262 |
DFyESNOW| 1 |VV |m.m^2/s |Meridional Diffusive Flux of eff snow thickn |
| 263 |
ADVxSSLT| 1 |UU |psu.m^2/s |Zonal Advective Flux of seaice salinity |
| 264 |
ADVySSLT| 1 |VV |psu.m^2/s |Meridional Advective Flux of seaice salinity |
| 265 |
DFxESSLT| 1 |UU |psu.m^2/s |Zonal Diffusive Flux of seaice salinity |
| 266 |
DFyESSLT| 1 |VV |psu.m^2/s |Meridional Diffusive Flux of seaice salinity |
| 267 |
\end{verbatim} |
| 268 |
} |
| 269 |
\caption{~} |
| 270 |
\end{table} |
| 271 |
|
| 272 |
|
| 273 |
%\subsubsection{Package Reference} |
| 274 |
|
| 275 |
\subsubsection{Experiments and tutorials that use seaice} |
| 276 |
\label{sec:pkg:seaice:experiments} |
| 277 |
|
| 278 |
\begin{itemize} |
| 279 |
\item{Labrador Sea experiment in lab\_sea verification directory. } |
| 280 |
\end{itemize} |
| 281 |
|
Parent Directory
| 
Revision Log
| 
Revision Graph