Energy balance of a glacier surface: analysis of Automatic Weather Station data from the Morteratschgletscher, Switzerland

Abstract

We describe and analyze a complete 1-yr data set from an automatic weather station (AWS) located on the snout of the Morteratschgletscher, Switzerland. The AWS stands freely on the glacier surface and measures pressure, windspeed, wind direction, air temperature and humidity, incoming and reflected solar radiation, incoming and outgoing longwave radiation, snow temperature, and change in surface height (giving melt rates and snow accumulation). The wind is downglacier most of the time. As expected for a flow of katabatic origin, for air temperatures above the melting point we find a correlation between windspeed and temperature. We evaluate all significant components of the surface energy flux. For a (constant) turbulent exchange coefficient of 0.00153 (reference height 3.5 m) we obtain a perfect match between calculated, and measured ice melt. The sensible heat flux is positive (towards the glacier surface) all the time with the largest values on fine summer days (daily mean values are typically 100 W M-2 on the warmest days). The latent heat flux is small and negative in winter. In summer it is mainly positive (condensation), but negative values also occur. Altogether about 75% of the melt energy is supplied by radiation (shortwave and longwave), and 25% by the turbulent fluxes.