Based on years of effort with mesoscale modeling in polar regions by the Polar Meteorology Group of the Byrd Polar Research Center at The Ohio State University, the Pennsylvania State University (PSU)-National Center for Atmospheric Research (NCAR) Fifth-generation Mesoscale Model (MM5) has been modified for use in polar regions (referred to as the Polar MM5). The key modifications are: · Revised cloud / radiation interaction · Modified explicit ice phase microphysics · Optimized turbulence (boundary layer) parameterization · Implementation of a sea ice surface type · Improved treatment of heat transfer through snow / ice surfaces. The nonhydrostatic Polar MM5 is now available as options in the public release version of MM5 (v3.5 and later) from NCAR. Here the applications of Polar MM5 in Antarctica are reviewed.

Forecasters use the model output as part of the National Science Foundation sponsored Antarctic Mesoscale Prediction System (AMPS) to meet the operational and logistic needs of the United States Antarctic Program (USAP) air operations. Under a collaborative project with the Polar Meteorology Group, AMPS simulations are performed at the NCAR twice per day, and cover progressively finer domains ranging from 90-km (covering most of the Southern Hemisphere) to 3-km (covering the region immediately surrounding McMurdo Station, the base of USAP operations).

Case studies, extended validations, and climatological investigations have demonstrated that Polar MM5 performs with skill on time scales from three hourly to interannual, both in the continental interior and coastal environment. Skill decreases for areas with complex (primarily coastal) terrain with spatial scales well below the model resolution. Notable recent applications include construction of initial 3-km resolution climatology of the Ross Island area based on 1-y of AMPS output that revealed for the first time the dominant impact of precipitation shadowing on the climate of the Dry Valleys region.

Recent Polar MM5 developments include the formulation of a new upper boundary condition that effectively damps the high wave activity of the Antarctic coastal environment and notably improves AMPS forecasts at longer time scales (1.5-3 days). Efforts are underway to enhance the calculation of the horizontal pressure gradient force for improved simulations of surface winds in areas of complex terrain and to alter the cloud-radiation interactions to eliminate residual biases in the surface temperature prediction. MM5 is transitioning to the Weather Research and Forecasting (WRF) model and plans are to migrate the polar physics to the WRF framework in the near future.