Probing Thermal Diffusivity and Microwave Extinction on Ice Sheet Surfaces Using Surface and Brightness Temperature Time Series

Time series of Antarctic surface temperature and 37 GHz, vertically polarized brightness temperature can be simply related by convolution and a single, characteristic time scale. The time scale is given by a ratio of thermal diffusivity and extinction length in near-surface firn (Winebrenner, Steig and Schneider, submitted to Ann. Glac., 2003). Here we investigate spatial and temporal variability in the characteristic time scale using Automated Weather Station data and satellite observations, at several locations in West Antarctica, and at times from late 1979 to the present. Observations at Byrd Station, for example, show no evidence of temporal variability during the period 1981-1987. The bounds on observed variability, together with physical modeling, can be used to bound variations in thermal diffusivity and microwave extinction length (which is, in this instance dominated by absorption) in both space and time. Those bounds allow us to place quantitative constrains on the interpretation of microwave brightness temperature data in terms of surface temperature. That interpretation in turn informs analysis of Antarctic climate variability, providing a calibration data set for statistical climate reconstruction from weather station data and from ice core observations acquired by the US-ITASE program.