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*                                                                         * 
*                                 GIM                                     *
*                         (The Global sea Ice Model)                      *
*                          Version 1.0, August  1999                      *
*                          Version 1.1, October 2005                      *
*          University of Washington copyright 1999. All rights reserved   *
*                                                                         *
*                       Software and Documentation                        *
*                                                                         *
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This software was developed at the Polar Science Center, Applied Physics
Laboratory (APL), University of Washington (UW). Support was provided by a
NASA EOS Interdisciplinary Investigation, POLar EXchange at the Sea surface
(POLES) Grant NAG5-4375. It is an evolving tool for climate study. Permission
is granted to other users to copy and use this software without charge, 
provided that this Notice and any statements of authorship are reproduced 
on all copies. Appropriate references should be made to Zhang and Rothrock
(2005) or Zhang and Hibler (1997) or Zhang and Rothrock (1999) if any 
part of the software is used. 
Those who wish to use the software should check the code carefully and make
sure that the assumptions, parameter choices, and numerical methods are
appropriate for their particular applications. The software is made available
'as is' and no support for its use is or will be provided by the UW or APL.
Neither the Government nor the University of Washington makes any warranty,
expressed or implied, or assumes any responsibility or liability for the 
use of this software. 

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GIM is a global dynamic thermodynamic sea ice model designed to represent 
the sea ice component in global climate models. GIM is coded based on a
spherical coordinate system derived by Zhang and Hibler (1997) with or 
without the north pole. It uses the ADI (alternating direction
implicit) numerical model to solve the sea ice momentum equations with a
teardrop plastic ice rheology with biaxial tensile stress (Zhang and Rothrock
2005). The ADI dynamics model is computationally efficient and rapidly approaches
a plastic solution (Zhang and Rothrock 1999). GIM version 1.1 is a two-
category seaice model with Semtner (1976) zero-layer thermodynamic calculations.
Later versions will include a multicategory thickness distribution model with
multilayer thermodynamic calculations. Please stay tuned.

A parallel version of this model has been developed and coupled to the
MIT ocean model. This parallel dynamic thermodynamic sea-ice model 
uses the LSR (line successive relaxation, Zhang and Hibler 1997) 
dynamics solver. See http://mitgcm.org.

If you find an error or if you have any comments, please contact 

      Jinlun Zhang,   zhang@apl.washington.edu 

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GIM History:

Written for the Arctic Ocean based on a rectangular coordinate system. 
Sea ice momentum equations solved by a point successive relaxation (PSR) 
technique. Elliptical yield curve used. (By Bill Hibler; see Hibler 1979).

Rewritten in spherical coordinate system; applied to global domain 
(By Jinlun Zhang 10/1993; see Zhang and Hibler 1997).

Finite differencing scheme for gracefully handling the North Pole singularity
included. (By Jinlun Zhang 9/1996).

Alternating direction implicit (ADI) technique used to solve sea ice
momentum equations (By Jinlun Zhang 10/1998; see Zhang and Rothrock 1999).

Teardrop plastic yield curve used for ice mechanics. (By Jinlun Zhang 10/2005;
see Zhang and Rothrock 2005).

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References:

Zhang, J. and D.A. Rothrock, The effect of sea-ice rheology in numerical 
   investigations of climate, J. Geophys. Res., 110, C08014, 
   doi:10.1029/2004JC002599, 2005.
Zhang, J. and D.A. Rothrock, Modeling Arctic Sea ice with an efficient
   plastic solution, accepted by J. Geophys. Res., 1999.
Zhang, J., and W.D. Hibler III, On an efficient numerical method for 
   modeling sea ice dynamics, J. Geophys. Res., 102, 8691-8702, 1997. 
Hibler, W. D. III, A dynamic thermodynamic sea ice model, J. Phys. 
   Oceanogr., 9, 815-846, 1979. 
Semtner, A. J., Jr., A model for the thermodynamic growth of sea ice in 
   numerical investigations of climate, JPO, 6, 379-389, 1976.

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Files:

GIM_UPDATES/
  README            this file
  run_gim.loop      primary run script for a job on an HP workstation or a PC_linux
  run_gim.1         run script called by run_gim.loop
  run_gim.2         run script called by run_gim.loop

  driver.F          main subroutine
  advect.F          solve conservation equations
  bndry.F           set up model domain
  budget.F          surface heat budget and ice growth rate
  diffus.F          calculate diffusion terms in conservation equations 
  form.F            prepare for solving momentum equations
  geo.F             read dynamic forcing
  groatb.F          read thermodynamic forcing
  growth.F          update sea ice thickness
  ice_1.F           time stepping
  ice_2.F           post-processing
  iomngr.F          file manager
  kmtbc.F           handle lateral boundaries
  mean.F            get mean values
  teardrop.F        calculate teardrop plastic sea ice rheology
  relax.F           solve momentum equations using the ADI numerical model
  rnegt.F           adjust ice thickness
  setice.F          model setup
  setup.F           set up files
  write_irestart.F  write restart file

  coord.h           model grid info, resolu. 2.4x1.2 deg in polar regions
  grdvar.h          model grid info
  levind.h          model grid info
  scalar.h          some constants
  setup.sh          script for setup
  size.h            model grid info
  size_ice.h        model grid info

  grid.dta          model grid data, lon and lat, etc.
  kmt.dta           model grid data, ocean mask: = 0, land; > 0, ocean level
  therm5.csm2x293_PC 1993 thermodynamic forcing: downward shortwave and longwave
                    radiations, surface air temperature, and specific 
                    humidity. All from the NCEP reanalysis.
                    used on a PC (the big-endian, little endian thing).
  wind.csm2x2.93_PC 1993 surface winds from the NCEP reanalysis.
  oflux.mon.csm2.dat ocean heat flux
  uo3.2x2.dat       ocean surface velocity

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Main variables:

uice, vice          ice velocity
eta, zeta           shear and bulk viscosities
drags, draga        quantities related to water drag 
amass               ice mass
forcex, forcey      external force
area                ice concentration
heff                ice thickness
hsno                snow thickness
tmix                temperature of ocean mixed layer
tice                ice temperature 
gairx, gairy        geostrophic wind velocity
gwatx, gwaty        surface geostrophic current velocity
heffm               ice thickness grid mask
uvm                 ice velocity frid mask
yneg                heat storage in ocean mixed layer, unit: meter of ice

Unit: SI: M-KG-S-K
