Abstract

A three-dimensional dynamic downscaling model of the Greenland atmospheric boundary layer, witha horizontal resolution of 20 km, is descibed and applied to the Greenland ice sheet for the 1998ablation season. The model uses ECMWF analysis data fields of synoptic pressure, free atmospherictemperature, cloud cover, humidity and sea surface temperature to force the model. The model calculatesthe perturbation component of the temperature and pressure field to describe the atmospheric boundarylayer dynamics. The aim of this study, the first of two papers, is to investigate the role of the turbulentheat fluxes in the surface energy balance of the ice sheet and their response to changes in atmospherictemperature. In this first paper, results from the simulation are compared with observations fromsix automatic weather stations situated on the ice sheet, three in the ablation zone and three in theaccumulation zone. The comparison shows that the boundary layer model can reproduce the nearsurfacemeteorological variables of wind, temperature and specific humidity quite well and improvesignificantly on 2 m values taken directly from the ECMWF analysis. The increased spatial resolutionof the model is essential in order to model accurately katabatically forced winds near the margin ofthe ice sheet. The calculated and observed melts at two sites in the ablation zone are also compared.At one site close to the margin, which is situated in a well drained ice region, the comparison withobservations is very good, within 1%. At a higher site, where subsurface processes not included in themodel are important for the total ablation, the calculated melt is 35% larger than the observed ablation.

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