Surface mass balance of the Greenland ice sheet from climate-analysis data and accumulation/runoff models

Abstract

We used surface climate fields from high-resolution (∼0.56 × 0.56°) European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses (1992-98), together with meteorological and glaciological models of snow accumulation and surface meltwater runoff/retention, to produce novel maps of Greenland ice sheet (GIS) net accumulation, net runoff and surface mass balance (SMB). We compared our runoff maps with similar-scaled runoff (melt minus refreezing) maps based on passive-microwave satellite data. Our gross spatial/temporal patterns of runoff compared well with those from the satellite data, although amounts of modelled runoff are likely too low. Mean accumulation was 0.287 (0.307) m a-1, and mean runoff was 0.128 (0.151) m a-1, averaged across the W. Abdalati (T. L. Mote) GIS mask. Corresponding mean SMB was 0.159 (0.156) m a-1, with considerable interannual variability (standard deviation ∼0.11 m a-1) primarily due to variations in runoff. Considering best estimates of current iceberg calving, overall the GIS is probably currently losing mass. Our study shows great promise for meaningfully modelling SMB based on forthcoming "second-generation" ECMWF re-analysis (ERA-40) data, and comparing the results with ongoing laser/radar measurements of surface elevation. This should help elucidate to what extent surface elevation changes are caused by short-term SMB variations or other factors (e.g. ice dynamics).