GMTB Common Community Physics Package (CCPP) Scientific Documentation  Version 1.0
GFS Sea Ice Scheme

Description

Sea ice is a thin skin of frozen water covering the polar oceans. The sea ice strongly interacts with both the atmosphere above and the ocean underneath in the high latitudes. In a coupled weather/climate system, changes in sea ice extent, thickness and concentration regionally or globally would influence oceanic and atmospheric conditions, which in turn affect the sea ice distribution. The physical and dynamical processes affecting the weather and climate are considered as follows:

  • The high albedo of the sea ice reflects more solar radiation back to the space. The feedbacks are considered as positive. The broader the sea ice cover, the higher the surface albedo, which result in less amount of solar radiation absorbed at the Earth's surface. A cooler surface would favor more sea ice to form. The process would be reversed in less sea ice situation.
  • The sea ice restricts the heat/water exchange between the air and ocean. The presence of extensive areas of sea ice would suppress the heat loss in winter and the heat gain in summer by the ocean. Even a thin ice cover influences the turbulent heat transfer significantly between ocean and atmosphere. The surface fluxes of sensible and latent heat can be greater by up to two orders of magnitude at the open water surface of a lead or polynya than that through (snow covered) pack ice.
  • The sea ice modifies air/sea momentum transfer, ocean fresh water balance and ocean circulation. The freezing and melting of the ocean surface and the associated fluxes of salt and heat produce major changes in the density structure of the polar water. Formation of sea ice injects salt into the ocean makes the water heavier and more convectively unstable, conversely when melting occurs, stable and fresh layers can prevent deep covective activity.

A sea ice model, in general, may contain subcomponents treating 1) dynamics (ice motion), 2) ice transport, 3) multiple ice thickness categories (including leads), 4) surface albedo, and 5) vertical thermodynamics. GFS sea ice scheme is concerned with a scheme for the last of these processes. A three-layer thermodynamic sea ice model ([84]) has been coupled to GFS. It predicts sea ice/snow thickness, the surface temperature and ice temperature structure. In each model grid box, the heat and moisture fluxes and albedo are treated separately for the ice and the open water.

Intraphysics Communication

General Algorithm