Case studies of katabatic wind in Coats Land, Antarctica

The ice cap of Antarctica loses heat due to radiative cooling at the surface, which then cools the overlying atmospheric boundary layer. The resulting (dense) layer of cold air will accelerate down the slope in response to a down-slope buoyancy force. These katabatic winds play a key role in the Antarctic surface wind regime.

The UKMO Unified Model (UM) version 6.1 has been used to simulate several case studies of katabatic wind situations in Coats Land, Antarctica. This region is located on the eastern shore of the Weddell Sea, and consists of the Brunt Ice Shelf and the adjoining continent to the south. Slopes are modest (5% at most), and katabatic winds are moderate (typically observed to be 7.5 m s-1 at the steepest part of the slope). Simulations of two case studies will be presented: from the 21-24 February 2002 (an Antarctic summer case) and 14 August 2003 (an Antarctic winter case). A large domain with a resolution of 12 km was run, followed by a one-way nested 4 km resolution domain centered on Halley research station. This setup made it possible to compare the model results to measurements from four Automatic Weather Stations (AWS's) as well as from an autonomous Doppler sodar wind profiling system, providing rare remotely sounded ABL wind profiles on the slope near Halley.

Initial results from the 4 km winter simulation are in reasonable agreement with observations. The model is able to simulate the katabatic flow along the slope, though wind speeds are often lower than those observed. The model also shows too cold surface temperatures over the ice shelf.