An Analysis of Strong Wind Events Simulated in a GCM near Casey in the Antarctic

Abstract

Strong wind events occurring near Casey (Antarctica) in a long July GCM simulation have been studied to determine the relative roles played by the synoptic situation and the katabatic flow in producing these episodes. It has been found that the events are associated with strong katabatic and strong gradient flow operating together. Both components are found to increase threefold on average for these strong winds, and although the geostrophic flow is the stronger, it rarely produces strong winds without katabatic flow becoming stronger than it is in the mean. The two wind components do not flow in the same direction; indeed, there is some cancellation between them, since katabatic flow acts in a predominant downslope direction, while the geostrophic wind acts across slope. The stronger geostrophic flow is associated with higher-than-average pressures over the continent and the approach of a strong cyclonic system toward the mast and a blocking system downstream. The anomalous synoptic patterns leading up to the occasions display a strong wavenumber 4 structure. The very strong katabatic flow appears to be related to the production of a supply of cold air inland from Casey by the stronger-than-average surface temperature inversions inland a few days before the strong winds occur. The acceleration of this negatively buoyant air mass down the steep, ice-sheet escarpment results in strong katabatic flow near the coast.