NSFlogo

Variability and Trends in Antarctic Sea Ice


Funded by NSF Antarctic Program
Jinlun Zhang
University of Washington


Home
Introduction Model
Data
Source Code
Publications
Links

Description of The Global Ice-Ocean Modeling and Assimilation System (GIOMAS)

The global sea ice data are produced by GIOMAS, which consists of a global Parallel Ocean and sea Ice Model (POIM, Zhang and Rothrock 2003) with data assimilation capabilities. The POIM is formulated in a generalized orthogonal curvilinear coordinate (GOCC) system and designed to run on computers with a single processor or massively parallel processors. The POIM couples the Parallel Ocean Program (POP) with a thickness and enthalpy distribution (TED) sea-ice model. The POP model is developed at the Los Alamos National Laboratory.

The TED sea-ice model is a dynamic thermodynamic model that also explicitly simulates sea-ice ridging. The model originates from the Thorndike et al. (1975) thickness distribution theory and is recently enriched by enthalpy distribution theory (Zhang and Rothrock, 2001). It has 8 categories each for ice thickness, ice enthalpy, and snow. This multicategory TED model consists of seven main components: a viscous-plastic ice rheology that determines the relationship between ice internal stress and ice deformation (Hibler 1979), a mechanical redistribution function that determines ice ridging (Thorndike et al. 1975; Rothrock, 1975; Hibler, 1980), a momentum equation that determines ice motion, a heat equation that determines ice growth/decay and ice temperature, an ice thickness distribution equation that conserves ice mass (Thorndike et al. 1975; Hibler, 1980), an ice enthalpy distribution equation that conserves ice thermal energy (Zhang and Rothrock, 2001), and a snow thickness distribution equation that conserves snow mass (Flato and Hibler, 1995). The ice momentum equation is solved using Zhang and Hibler's (1997) ice dynamics model that employs a line successive relaxation technique with a tridiagonal matrix solver, which has been found to be particularly useful for parallel computing (Zhang and Rothrock, 2003). The heat equation is solved over each ice thickness category using a modified three-layer thermodynamic model (Winton, 2000).

Satellite sea ice concentration data are assimilated in GIOMAS using the Lindsay and Zhang (2005) assimilation procedure. The procedure is based on “nudging” the model estimate of ice concentration toward the observed concentration in a manner that emphasizes the ice extent and minimizes the effect of observational errors in the interior of the ice pack.

The configuration of the finite-difference grid of GIOMAS is shown below.

Atlantic Pacific Grid

Atlantic Pacific Grid

The horizontal dimension of the model is 360×276. In the southern hemisphere the model grid is based on a spherical coordinate system. In the northern hemisphere the model grid is a stretched GOCC grid with the northern grid pole displaced into Greenland. This allows the model to have its highest resolution in the Greenland Sea, Baffin Bay, and the eastern Canadian Archipelago, and therefore a  good connection between the Arctic Ocean and the Atlantic Ocean via the Greenland-Iceland-Norwegian (GIN) Sea and the Labrador Sea. The model was driven by the NCEP/NCAR reanalysis data.

References

Thorndike, A. S., D. A. Rothrock, G. A. Maykut, and R. Colony, 1975: The thickness distribution of sea ice. J. Geophys. Res., 80, 4501-4513.

Hibler, W. D. III, 1979: A dynamic thermodynamic sea ice model. J. Phys. Oceanogr., 9, 815-846.

Hibler, W. D. III, 1980: Modeling a variable thickness sea ice cover. Mon. Wea. Rev., 108, 1943-1973.

Flato, G. M., and W. D. Hibler, III, 1995: Ridging and strength in modeling the thickness distribution of Arctic sea ice. J. Geophys. Res., 100, 18,611-18,626.

Winton, M., 2000: A reformulated three-layer sea ice model. J. Atmos. Ocean. Tech., 17, 525-531.

Back to TOP

Home
Introduction Model
Data
Source Code
Publications
Links