Forcing of the wintertime antarctic boundary layer winds from the NCEP-NCAR global reanalysis

Antarctica is noted for strong and persistent winds in the lower atmosphere . The wind directions are controlled by the underlying ice terrain and are deflected in general 20 degrees -50 degrees to the left of the fall line. T he Antarctic surface wind regime is thought to be the result of the dual in fluences of diabatic cooling of the terrain, responsible for the infamous k atabatic winds, and the synoptic pressure gradient force in the free atmosp here. The relative importance of pressure gradients associated with katabat ic and synoptic processes in forcing the wintertime Antarctic boundary laye r winds is evaluated using output from the National Centers for Environment al Prediction-National Center for Atmospheric Research (NCEP-NCAR) global r eanalysis program for June, July, and August of 1997. Both katabatic and sy noptic forces are found to be significant in shaping the near-surface winte r winds over the Antarctic ice slopes. Analyses show that the synoptic forc e is influenced by the underlying ice terrain such that the net force over Antarctica is directed primarily downslope. This result reflects the adjust ment of the large-scale ambient pressure gradient to the continental orogra phy. The synoptic force over Antarctica thus differs significantly in both magnitude and direction from that found over the oceanic regions to the nor th. The adjustment of the synoptic force over the ice sheets enable even th e nonwinter Antarctic winds to attain a high directional constancy and rese mble a gravity-driven flow. This process also suggests that direction alone is insufficient in classifying Antarctic flows as katabatic.