Sea ice in the NCEP forecast system


Sea ice is an integral component of the global climate and weather system. The extent of sea ice is mainly influenced by, and has a significant effect on, the surface energy budget, ocean-atmosphere energy exchange, and ocean fresh water balance. Regional and global changes in sea ice fraction and extent influence oceanic and atmospheric conditions, which in turn influence the evolution of sea ice itself. The issues related to sea ice forecast include data assimilation; model initial condition; sea ice models; and the coupling processes between the ice and ocean, and the ice and atmosphere.

The configuration of sea ice in NCEP forecasts system will be reviewed. At present a three-layer thermodynamic sea ice model is coupled to NCEP global forecast system (GFS). Current sea ice initial conditions are specified using analysis (pure algorithm) rather than assimilation. It produces a 5 minutes lat-long grid from the 85GHz SSMI information. The GFS is currently using the half degrees version of the product. For the Real Time Ocean Forecast System (RTOFS), it is an Atlantic domain only regional model without sea ice component. For the Climate Forecast System (CFS), sea ice is treated in a very simple way, fixed at 3 m depth with 100% concentration.

The development plan for sea ice in NCEP forecasts system will be discussed. We will describe the global version of RTOFS that includes sea ice; CFS with a dynamic thermodynamic sea ice model; and GFS with improved treatment of sea ice. The future system will also include a sea ice assimilation system, starting with sea ice concentration.

Xingren Wu and Robert Grumbine