Precipitation over the Interior East Antarctic Ice Sheet Related to Midlatitude Blocking-High Activity

Intermittent atmospheric blocking-high activity in the South Tasman Sea is shown to play a key role in delivering substantial snowfall as far south as at least 75°S on the central East Antarctic Ice Sheet plateau. Typically, cyclones fail to penetrate this far (> 1000 km) inland, and accumulation was thought to be dominated by clear-sky precipitation. In East Antarctica, the meridional cloud bands delivering the moisture originate from as far north as 35°-40°S, and appear to preferentially pass over the East Antarctic coast in a corridor from ∼ 120° to 160°E. Comparison of surface observations, model, and satellite data suggests that a few such episodes contribute a significant proportion of the (low) mean annual accumulation of the central East Antarctic Ice Sheet (e.g., an estimated 44% at Dome C over 18 days in December 2001-January 2002). Blocking-high-related incursions also cause abrupt increases in the surface wind speed (snow redistribution) and air temperature; this has implications for the interpretation of ice core data. Blocking-high-related precipitation episodes can generally be detected over the ice sheet interior, via abrupt changes (of ∼0.02-0.04) in polarization in 37- and 85-GHz SSM/I data, due to the relative stability of the surface and its "background" microwave signature and the relative lack of cloud cover overall. This is not the case in high-accumulation near-coastal regions such as Law Dome, where additional information is required. Ambiguities remain due to blowing snow and hoarfrost formation. Further research is necessary to examine the frequency of occurrence and variability of midlatitude blocking-high systems, their effect on precipitation in the Antarctic Ice Sheet interior, and the potential effect of global change.