Factors Controlling the Near-Surface Wind Field in Antarctica

Abstract

Using data from the regional atmospheric climate model RACMO/ANT1 the momentum budget of the Antarctic atmospheric surface layer (SL; taken as the lowest model layer located at 6?7 m above the surface) is presented. In July (winter), the katabatic pressure gradient force (PGF) dominates the SL momentum budget over the steep coastal slopes, which results in strong (10?15 m s?1) and directionally constant katabatic winds. Farther inland, where surface slopes are more gentle, the large-scale PGF may become equally important. With the circumpolar pressure trough north of the Antarctic coastline, the large-scale PGF acts along with the katabatic PGF in the downslope direction. In Wilkes Land, Dronning Maud Land, and on the western Ross Ice Shelf, the large-scale PGF causes equivalent geostrophic winds in excess of 10 m s?1. Thermal wind effects that oppose the downslope acceleration are especially strong in areas where large-scale forcing is weak, which allows cold air to pile up over the flat ice shelves and sea ice?covered ocean. In January, absorption of shortwave radiation at the surface strongly reduces the katabatic forcing and thermal wind effects, and the large-scale PGF dominates the SL momentum budget. Interestingly, large-scale easterly winds in some regions are stronger in summer than in winter, which explains the year-round constancy of Antarctic SL winds. In contrast, the large-scale SL winds in coastal West Antarctica and the Antarctic Peninsula are very variable on the seasonal timescale.