Author:

Keywords:

Science & Technology, Physical Sciences, Meteorology & Atmospheric Sciences, REGIONAL ATMOSPHERIC MODEL, KATABATIC WINDS, ADELIE LAND, BOUNDARY-LAYER, TEMPERATURE INVERSION, SOUTHERN-HEMISPHERE, WEST ANTARCTICA, EAST ANTARCTICA, SIPLE COAST, ICE SHELF, 0102 Applied Mathematics, 0401 Atmospheric Sciences, 3701 Atmospheric sciences

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.