s_phys_pkgs/text/seaice.tex

% $Header:  $
% $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}

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