Spatial and temporal variability of net snow accumulation over the Antarctic from ECMWF re-analysis project data

Forecasts from the ECMWF re-analysis project (ERA) covering the period 1979 -1993 are used to examine the spatial and temporal distribution of net snow accumulation (precipitation minus evaporation) over the Antarctic continen t. There is generally good agreement between the spatial distribution of ne t accumulation in the model data, when the 15 year mean annual accumulation is considered, and the equivalent maps produced in earlier studies from in situ data. One of the major differences is the westerly displacement of th e accumulation maximum on the western side of the Antarctic Peninsula as a result of the model orography having a high degree of smoothing in the east -west direction. The mean annual net accumulation in the ERA data for the w hole of the continent is 151 mm year(-1), equivalent to a total accumulatio n of 2106 x 10(12) kg year(-1). The mean accumulation value is in reasonabl e agreement with the best estimates from glaciological data, which recent s tudies have suggested is in the range 150-170 mm year(-1). The lower value from ERA is partly a result of overestimation of evaporation/sublimation fr om the large ice shelves during the summer and spring, and an underestimati on of the precipitation in the interior of the continent. The accumulation from the ERA data is the same as that computed from the operational ECMWF f orecasts. During the 15 year data period, the mean accumulation varied from 129.1 mm (1987) to 171.8 mm (1984). Considering the continent as a whole, net accumulation was at a minimum in the summer season, although in coastal parts of West Antarctica, the minimum occurs in spring. The ERA accumulati on data for the interior of the continent show no annual cycle and are sign ificantly smaller than the available in situ measurements. At certain coast al sites in West Antarctica there is a clear relationship between annual pr ecipitation and cyclone activity, although in East Antarctica such a relati onship is only apparent in monthly data. Copyright (C) 1999 Royal Meteorolo gical Society.