Antarctic Snowmelt Detected by Diurnal Variations of AMSR-E Brightness Temperature

Abstract

Antarctic surface snowmelt is sensitive to the polar climate. The ascending and descending passes of the Advanced Microwave Scanning Radiometer for Earth Observing System Sensor (AMSR-E) observed the Antarctic ice sheet in the afternoon (the warmest period) and at midnight (a cold period), enabling us to make full use of the diurnal amplitude variations (DAV) in brightness temperature (Tb) to detect snowmelt. The DAV in vertically polarized 36.5 GHz Tb (DAV36V) is extremely sensitive to liquid water and can reduce the effects of the structural changes in snowpacks during melt seasons. A set of controlled experiments based on the microwave emission model of layered snow (MEMLS) were conducted to study the changes of the vertically polarized 36.5 GHz Tb (Δ36V) during the transitions from dry to wet snow regimes. Results of the experiments suggest that 9 K can be used as a DAV36V threshold to recognize snowmelt. The analyses of snowmelt suggest that the Antarctic ice sheet began to melt in November and became almost completely frozen in late March of the following year. The total cumulative melt area from 2002 to 2011 was 2.44 × 106 km2, i.e., 17.58% of the Antarctic ice sheet. The annual cumulative melt area showed considerable fluctuations, with a significant (above 90% confidence level) drop of 5.24 × 104 km2/year in the short term. Persistent snowmelt (i.e., melt that continues for at least three days) detected by AMSR-E and hourly air temperatures (Tair) were very consistent. Though melt seasons became longer in the western Antarctic Peninsula and the Shackleton Ice Shelf, Antarctica was subjected to considerable decreases in duration and melting days in stable melt areas, i.e., −0.64 and −0.81 days/year, respectively. Surface snowmelt in Antarctica decreased temporally and spatially from 2002 to 2011.