A COMPARISON OF MICROWAVE RADIOMETRIC DATA AND MODELED SNOWPACK CONDITIONS FOR DYE-2, GREENLAND

Meteorological observations were recorded at Dye 2, Greenland, during the summer of 1993 as part of a research program to identify interannu al variations in melt occurrence on the Greenland ice sheet from satel lite microwave data. The meteorological observations were used to driv e an energy-balance model of the snowpack during 21 June to 13 July 19 93. Time series of the meteorological observations and various model o utputs were compared to a concurrent time series of Special Sensor Mic rowave/Imager (SSM/I) data for scan cells centered within 25 km of Dye 2. The satellite microwave observations clearly show an increase in s nowpack emissivity at the same time that the model indicates liquid wa ter forming in the snow. Diurnal melt-freeze cycles that occurred duri ng mid June to early July resulted in an increase in the 37 GHz bright ness temperature as great as 60 K from the dry, refrozen snow in the m orning to the wet snow of some afternoons. The effects of fresh snowfa ll, which tend to increase the brightness temperature, and of snow gro wth from melt-freeze metamorphism, which tend to decrease the brightne ss temperature, are also apparent in the microwave observations. The r esults of this work demonstrate the influence of daily weather variati ons on the microwave emissivity in the ice sheet's percolation zone an d the usefulness of swath data to diagnose the diurnal cycle of melt.