Conditions for Strong Wind Occurrences at Casey

Full description

This set is taken from a long simulation with a General Circulation Model. The extract used here is the pressure and temperature analyses of the 3d simulated atmosphere on days upon which strong surface winds are simulated at Casey.

Taken from the abstract of the referenced paper:

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 coast 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.

Lineage

Progress Code: completed

Statement: Values provided in temporal coverage are approximate only. The GCM used in this study is a 21-wave version based on that described by Simmonds (1985) and was run in 'perpetual' July mode. It has been shown to provide an excellent simulation not only of high southern latitude mean climate, but also captures the main characteristics of synoptic- and longer-scale variability. See the paper for more information.