An extreme wind event at Casey Station, Antarctica

Model output, satellite data, and in situ observations are used to investig ate the conditions that gave rise to an extreme wind event at the Australia n Casey Station (66.27 degrees S, 110.53 degrees E) on the coast of East An tarctica. The event took place over the period March 20-22, 1992, and resul ted in Casey Station's highest ever wind gust for March (66.9 m s(-1), 130 knots) and 10 m mean winds of near 50 m s(-1). The event occurred when a de ep low was located just north of the coast and there was high surface press ure inland. The rapid deepening of the low took place within a strong baroc linic zone lying north-south between a cold trough and a ridge bringing ver y warm air southward. A conceptual model is proposed for the very strong wi nds experienced at Casey Station. Key elements of the model are (1) a synop tic-scale high-low pressure couplet, providing a strengthening pressure gra dient; (2) entrainment of radiatively cooled air by the supercritical synop tic gradient, leading to downslope flow; (3) the acceleration of the wind d own the lee slope of Law Dome, occurring primarily in response to a topogra phically induced, long-period, vertically propagating gravity wave; and (4) sources of negative buoyancy, including prestorm radiatively cooled air an d, later in the storm, maritime air cooled by heat flux to the ice surface. The topographically induced gravity wave increases the horizontal temperat ure difference, thus increasing the negative buoyancy of the surface airflo w.