Recent changes in pan-Antarctic surface snowmelt detected by AMSR-E and AMSR2

Abstract. Surface snowmelt in the pan-Antarctic, including the Antarctic sea ice and ice sheet, is crucial to the mass and energy balance in polar regions and can serve as an indicator of climate change. We investigated the spatial and temporal variations of the surface snowmelt over the entire pan-Antarctic as a whole from 2002 to 2017 by using the passive microwave remote sensing data. The stable orbit and appropriate acquisition time of the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) and the Advanced Microwave Scanning Radiometer 2 (AMSR2) enable us to take full advantage of the daily brightness temperature (Tb) variations to detect the surface snowmelt events. In this study, diurnal amplitude variations of AMSR-E/2 vertically polarized 36.5 GHz Tb (DAV36V) were utilized to map the pan-Antarctic snowmelt because it is unaffected by the snow metamorphism. We validated the DAV36V method against the ground-based measurements and further improved the method over the marginal sea ice zone by excluding the effect of open water. Snowmelt detected by AMSR-E/2 data agreed well with that derived by ERA-Interim reanalysis, and much more extensive than that detected by the Special Sensor Microwave/Imager (SSM/I) data. On average, pan-Antarctic snowmelt began on 19 September, and experienced 32 melt events. Annual mean melt extent on the Antarctic ice sheet (AIS) was only 9 % of that on the Antarctic sea ice. Overall, the pan-Antarctic surface snowmelt showed a trend (at 95 % confidence level) toward later melt onset (0.70 days yr−1) during the 2002–2017 period. Surface snowmelt was well correlated with atmospheric indices in some regions. Notably, the decreasing surface snowmelt on the AIS was very likely linked with the enhancing summer Southern Annular Mode.