Satellite, Observational, Meteorological and Thermal Records From Two Sites in the Antarctic Megadunes - Stability of Atmospheric Forcing, Thermal Cracking, and the Seasonal Evolution of the Thermal Profile

An NSF-OPP funded research site in the megadunes occupied during the 2002-2003 and 2003-2004 field seasons provided an opportunity to monitor wind speed and direction, atmospheric pressure, air temperature, and the evolution of the thermal profile in the firn. In the first season this was done on the lee face of a megadune; in the second season it was done there and at an additional site on the windward face. Wind speed and temperature fluctuations were well correlated at the two sites with little lag. The thermal profiles provide a picture of the cold wave penetration at both sites. Firn in these areas was significantly recrystallized (see abstract by Courville et al., this session), had a surface character that included both large sastrugi (windward slopes) and very smooth surfaces (lee slopes), and showed numerous thermal contraction cracks that were likely sites of vertical air movement. In the first season the smooth lee slope was covered by a thin glaze; the spatial extent of this glaze and the surface roughness variations are detectable in satellite imagery from this period. Large area MODIS-based image maps show the dominance of katabatic-wind-generated features in the dune field. Satellite-based microwave emission time series show the source of emission to be extremely shallow and/or characteristic of rapid cooling to near isothermal conditions; these patterns have been used to map the extent of recrystallized firn. This will be revisited in light of the new time series of firn thermal profiles.