The surface climatology of an ordinary katabatic wind regime in Coats Land, Antarctica

Abstract

The surface climatology of Coats Land, Antarctica, is described through observations from automaticweather 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 ofthis region is typical of much of the Antarctic coastal fringes: a modest slope (5% at most) and relativeuniformity across the slope. A basic climatology broken into site and season is presented. In winter, andto an extent in the equinoctial seasons, the region clearly divides into two dynamical regimes. Over theice shelf winds are usually from the east or occasionally from the west, whereas over the continentalslopes winds are from the east to south quadrant. Over the ice shelf the surface layer is about 10 Kcolder, in terms of potential temperature, than on the continent, and is also more stable than on thesteeper parts of the slope. Motivated by case studies, three criteria are developed to select a subset ofthe data that are katabatic in the sense that the flow is believed to be primarily due to a downslopebuoyancy forcing. On the continental slope, the criteria pick out a coherent subset of the data that aretightly clustered in wind speed and wind direction. Typical katabatic winds are from 10° to the east ofthe fall line and 7.5 m s-1 at the steepest part of the slope (5.1 m s-1 higher up). They are rarely morethan 15 m s-1 in this region; hence their description as ordinary, in contrast with those extraordinarykatabatic regimes that have been the focus of previous studies. The katabatic flow remains close toadiabatic as it moves down the slope, and is relatively dry near the slope foot. We estimate the flow tobe primarily katabatic at most 40—50% of the time, although it may appear to be katabatic, from windspeed and wind direction characteristics, some 60—70% of the time. There is no coherent katabatic-flowsignature on the ice shelf.