s_phys_pkgs/text/seaice.tex

% $Header: /u/gcmpack/manual/part6/seaice.tex,v 1.1 2004/08/30 19:25:41 edhill Exp $
% $Name:  $

%%EH3  Copied from "MITgcm/pkg/seaice/seaice_description.tex"
%%EH3  which was written by Dimitris M.


\section{Sea Ice Package: ``seaice''}
\label{sec:pkg:seaice}
\begin{rawhtml}
<!-- CMIREDIR:package_seaice: -->
\end{rawhtml}

Package ``seaice'' provides a dynamic and thermodynamic interactive
sea-ice model.  Sea-ice model thermodynamics are based on Hibler
\cite{hib80}, that is, a 2-category model that simulates ice thickness
and concentration.  Snow is simulated as per Zhang et al.
\cite{zha98a}.  Although recent years have seen an increased use of
multi-category thickness distribution sea-ice models for climate
studies, the Hibler 2-category ice model is still the most widely used
model and has resulted in realistic simulation of sea-ice variability
on regional and global scales.  Being less complicated, compared to
multi-category models, the 2-category model permits easier application
of adjoint model optimization methods.

Note, however, that the Hibler 2-category model and its variants use a
so-called zero-layer thermodynamic model to estimate ice growth and
decay.  The zero-layer thermodynamic model assumes that ice does not
store heat and, therefore, tends to exaggerate the seasonal
variability in ice thickness.  This exaggeration can be significantly
reduced by using Semtner's \cite{sem76} three-layer thermodynamic
model that permits heat storage in ice.  Recently, the three-layer
thermodynamic model has been reformulated by Winton \cite{win00}.  The
reformulation improves model physics by representing the brine content
of the upper ice with a variable heat capacity.  It also improves
model numerics and consumes less computer time and memory.  The Winton
sea-ice thermodynamics have been ported to the MIT GCM; they currently
reside under pkg/thsice.  At present pkg/thsice is not fully
compatible with pkg/seaice and with pkg/exf.  But the eventual
objective is to have fully compatible and interchangeable
thermodynamic packages for sea-ice, so that it becomes possible to use
Hibler dynamics with Winton thermodyanmics.

The ice dynamics models that are most widely used for large-scale
climate studies are the viscous-plastic (VP) model \cite{hib79}, the
cavitating fluid (CF) model \cite{fla92}, and the
elastic-viscous-plastic (EVP) model \cite{hun97}.  Compared to the VP
model, the CF model does not allow ice shear in calculating ice
motion, stress, and deformation.  EVP models approximate VP by adding
an elastic term to the equations for easier adaptation to parallel
computers.  Because of its higher accuracy in plastic solution and
relatively simpler formulation, compared to the EVP model, we decided
to use the VP model as the dynamic component of our ice model.  To do
this we extended the alternating-direction-implicit (ADI) method of
Zhang and Rothrock \cite{zha00} for use in a parallel configuration.

The sea ice model requires the following input fields: 10-m winds, 2-m
air temperature and specific humidity, downward longwave and shortwave
radiations, precipitation, evaporation, and river and glacier runoff.
The sea ice model also requires surface temperature from the ocean
model and third level horizontal velocity which is used as a proxy for
surface geostrophic velocity.  Output fields are surface wind stress,
evaporation minus precipitation minus runoff, net surface heat flux,
and net shortwave flux.  The sea-ice model is global: in ice-free
regions bulk formulae are used to estimate oceanic forcing from the
atmospheric fields.


%\subsection{Package Reference}

1	% $Header: /u/gcmpack/manual/part6/seaice.tex,v 1.1 2004/08/30 19:25:41 edhill 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	\section{Sea Ice Package: ``seaice''}
9	\label{sec:pkg:seaice}
10	\begin{rawhtml}
11	<!-- CMIREDIR:package_seaice: -->
12	\end{rawhtml}
13
14	Package ``seaice'' provides a dynamic and thermodynamic interactive
15	sea-ice model. Sea-ice model thermodynamics are based on Hibler
16	\cite{hib80}, that is, a 2-category model that simulates ice thickness
17	and concentration. Snow is simulated as per Zhang et al.
18	\cite{zha98a}. Although recent years have seen an increased use of
19	multi-category thickness distribution sea-ice models for climate
20	studies, the Hibler 2-category ice model is still the most widely used
21	model and has resulted in realistic simulation of sea-ice variability
22	on regional and global scales. Being less complicated, compared to
23	multi-category models, the 2-category model permits easier application
24	of adjoint model optimization methods.
25
26	Note, however, that the Hibler 2-category model and its variants use a
27	so-called zero-layer thermodynamic model to estimate ice growth and
28	decay. The zero-layer thermodynamic model assumes that ice does not
29	store heat and, therefore, tends to exaggerate the seasonal
30	variability in ice thickness. This exaggeration can be significantly
31	reduced by using Semtner's \cite{sem76} three-layer thermodynamic
32	model that permits heat storage in ice. Recently, the three-layer
33	thermodynamic model has been reformulated by Winton \cite{win00}. The
34	reformulation improves model physics by representing the brine content
35	of the upper ice with a variable heat capacity. It also improves
36	model numerics and consumes less computer time and memory. The Winton
37	sea-ice thermodynamics have been ported to the MIT GCM; they currently
38	reside under pkg/thsice. At present pkg/thsice is not fully
39	compatible with pkg/seaice and with pkg/exf. But the eventual
40	objective is to have fully compatible and interchangeable
41	thermodynamic packages for sea-ice, so that it becomes possible to use
42	Hibler dynamics with Winton thermodyanmics.
43
44	The ice dynamics models that are most widely used for large-scale
45	climate studies are the viscous-plastic (VP) model \cite{hib79}, the
46	cavitating fluid (CF) model \cite{fla92}, and the
47	elastic-viscous-plastic (EVP) model \cite{hun97}. Compared to the VP
48	model, the CF model does not allow ice shear in calculating ice
49	motion, stress, and deformation. EVP models approximate VP by adding
50	an elastic term to the equations for easier adaptation to parallel
51	computers. Because of its higher accuracy in plastic solution and
52	relatively simpler formulation, compared to the EVP model, we decided
53	to use the VP model as the dynamic component of our ice model. To do
54	this we extended the alternating-direction-implicit (ADI) method of
55	Zhang and Rothrock \cite{zha00} for use in a parallel configuration.
56
57	The sea ice model requires the following input fields: 10-m winds, 2-m
58	air temperature and specific humidity, downward longwave and shortwave
59	radiations, precipitation, evaporation, and river and glacier runoff.
60	The sea ice model also requires surface temperature from the ocean
61	model and third level horizontal velocity which is used as a proxy for
62	surface geostrophic velocity. Output fields are surface wind stress,
63	evaporation minus precipitation minus runoff, net surface heat flux,
64	and net shortwave flux. The sea-ice model is global: in ice-free
65	regions bulk formulae are used to estimate oceanic forcing from the
66	atmospheric fields.
67
68
69	%\subsection{Package Reference}
70