The surface climatology of an ordinary katabatic wind regime in Coats Land, Antarctica
The surface climatology of Coats Land, Antarctica, is described through observations from automatic weather stations, from Halley station, from upper air soundings and from satellite remote sensing. Coats Land consists of the Brunt Ice Shelf and the adjoining continent to the South. The topography of this region is typical of much of the Antarctic coastal fringes: a modest slope (5% at most) and relative uniformity across the slope. A basic climatology broken into site and season is presented. In winter, and to an extent in the equinoctial seasons, the region clearly divides into two dynamical regimes. Over the ice shelf winds are usually from the east or occasionally from the west, whereas over the continental slopes winds are from the east to south quadrant. Over the ice shelf the surface layer is about 10 K colder, in terms of potential temperature, than on the continent, and is also more stable than on the steeper parts of the slope. Motivated by case studies. three criteria are developed to select a subset of the data that are katabatic in the sense that the flow is believed to be primarily due to a downslope buoyancy forcing. On the continental slope, the Criteria pick out a coherent Subset of the data that are tightly clustered in wind speed and wind direction. Typical katabatic winds are from 10degrees to the east of the fall line and 7.5 ms(-1) at the steepest part of the slope (5.1 ms(-1) higher up). They are rarely more than 15 ms(-1) in this region; hence their description as ordinary, in contrast with those extraordinary katabatic regimes that have been the focus of previous studies. The katabatic flow remains close to adiabatic as it moves down the slope, and is relatively dry near the slope foot. We estimate the flow to be primarily katabatic at most 40-50% of the time, although it may appear to be katabatic, from wind speed and wind direction characteristics, some 60-70% of the time. There is no coherent katabatic-flow signature on the ice shelf.