A general circulation model study of the orographic gravity waves over Antarctica excited by katabatic winds

Abstract

In this study, we simulated orographic gravity waves (OGWs) over Antarctica using a T213L250 general circulation model (GCM). The GCM has a fine vertical resolution of 300 m throughout the middle atmosphere. The simulation was run for a 1-year period. Results from 21-28 June were primarily considered. OGWs are excited by katabatic winds that travel down the surface slopes of the Antarctic ice sheet. A strong eastward katabatic wind blows over the west coast of the Ross Sea at the approach of the synoptic-scale upper tropospheric westerly jets. A quasi-stationary OGW is then excited above the coast and propagates upward into the mesosphere. An OGW appears sporadically during the Antarctic winter and spring. Its amplitude is determined by the strength of the eastward katabatic wind. Dissipation of OGWs within the middle atmosphere results in a localized deceleration of westerly winds, greater than - 30 m s -1 d -1. This in turn modifies the horizontal circulation in the polar vortex. Strong vertical mixing occurs withmi the mesosphere and is associated with wave breaking. Large temperature fluctuations associated with the OGWs affect the formation or suppression of polar stratospheric clouds in the lower stratosphere. Katabatic wind excitation is the most powerful source of gravity waves over Antarctica around the time of the winter solstice. Copyright 2006 by the American Geophysical Union.