Ablation rate estimates over the Greenland ice sheet from microwave radiometric data

Scanning Multichannel Microwave Radiometer (SMMR) data are used to estimate the annual melt duration (number of days with melt) for elevation transect s over the Greenland ice sheet during the period from 1979-1986. The annual melt duration is used to estimate the number of positive degree days (PDDs ), which are used in a degree-day mass balance model to determine ablation rates and the equilibrium line altitude (ELA). The annual melt duration alo ng two transects estimated with SMMR data compares favorably, particularly above the ELA to melt duration calculated from surface temperature data far the same locations. The mass balance estimates and ELA locations along eig ht transects agree reasonably well with measurements reported in previous s tudies using surface temperature data. ELAs were within 10m of published va lues along two transects, and the root mean square error of SMMR-derived ve rsus surface mass balance measurements was 43mm yr(-1). The estimated error in SMMR-derived ablation is between +/-15% and +/-50%, but could be reduce d substantially by using daily microwave data available from the Special Se nsor Microwave/Imager (SSM/I). This research shows the feasibility of using passive microwave data to estimate the ablation rate in order to determine ELA, which can be used to monitor the mass balance of the ice sheet.