A link between microwave extinction length, firn thermal diffusivity, and accumulation rate in West Antarctica

Abstract

The relationship between time series of physical surface temperature and microwave brightness temperature of polar firn depends both on the physical properties of the firn and the surface temperature history. In perennially dry firn this relationship is well characterized by a timescale, referred to as the extinction-diffusion time, which is the ratio of the microwave extinction length squared to the firn thermal diffusivity. The extinction-diffusion time is calculated over Antarctica from 1982 to 1999 by comparing thermal infrared observations of physical surface temperature from the advanced very high resolution radiometer (AVHRR) with passive microwave brightness temperatures measured by the scanning multichannel microwave radiometer (SMMR) and Special Senor Microwave Imager (SSM/I). Independent estimates of accumulation rate are derived both from ice cores and from spatially extensive ground and airborne radar echo sounding lines. The extinction-diffusion time is found to vary linearly with accumulation rate from approximately 10 to 50 cm/yr ice equivalent over a large area in West Antarctica. Although this simple relationship does not appear to hold at very low or very high accumulation rates, these results suggest that the extinction-diffusion time holds promise as a viable proxy for accumulation rate variability on polar ice sheets. Copyright 2007 by the American Geophysical Union.