A CASE-STUDY OF ANTARCTIC KATABATIC WIND INTERACTION WITH LARGE-SCALEFORCING

Surface pressure decreases of up to 20 hPa occurred over much of the A ntarctic continent during a 4-day midwinter period of 1988. The widesp read change in the pressure held accompanied intense cyclonic activity to the north of the ice sheet. The equatorward mass transport across the Antarctic coastline resulted in a redistribution of atmospheric pr essure that extended to the subtropics of the Southern Hemisphere. Mos t of the mass flux from Antarctica was the result of low-lever process es and appears tied to the katabatic wind circulation. The observed su rface pressure decrease over the continent reflects a perturbation of the mean meridional circulation between Antarctica and the subpolar la titudes by synoptic-scale processes. Zonally averaged circulations ove r Antarctica were examined using output from the European Centre for M edium-Range Weather Forecasts model. Results suggest that only a poorl y defined return branch of the meridional circulation exists in the mi ddle and upper troposphere. This southward-directed flow does not comp ensate for the northward mass transport provided by the katabatic wind outflow in the lower atmosphere. Isallobaric contours over the Antarc tic ice sheet roughly match the area of the large-scale drainage catch ment associated with katabatic wind transport through the Ross Sea sec tor. An intense extratropical cyclone was present in the circumpolar o ceanic belt to the north of the continent. The horizontal pressure gra dient associated with the cyclone prompted enhanced drainage off the h igh interior plateau. The resulting katabatic flow issued from the con tinent through a narrow corridor across the Ross Ice Shelf and out ove r the Southern Ocean.