Hemispheric Contrasts in the Trait of Snowmelt on Sea Ice as Indicated Through Microwave Satellite Data

The succession of the different phenomenological stages of snow on sea ice during the melt period and the contribution of each stage to total surface melt is of great interest for sea-ice monitoring studies. In the Arctic, snow disappears quickly once the melt season has started. An early melt stage is characterized by freeze- thaw cycles and marks a short transition between the pre-melt and melt phase. In contrast, the early melt stage with pronounced freeze-thaw cycles is prevailing the surface melt period throughout the whole summer in the Antarctic and persistent snowmelt is very rare. This hemispheric difference impedes a transfer of melt detection methods that were successfully applied in the Arctic. To identify snowmelt on sea ice in the Southern Ocean, we introduce a diurnal-difference melt indicator based on microwave brightness temperatures. This accounts for the characteristic phenomenological stages of snowmelt on Antarctic sea ice and detects the onset of diurnal snow wetting, the early melt stage respectively. Applied to the period from 1988 to 2007, we obtain results that indicate a high regional and interannual variability in distinctiveness and onset of this stage. Applied also to sea ice in the Arctic, where freeze-thaw cycles just played a minor role in previous melt studies, our method provides insight into the hemispheric contrast of the evolution and strength of surface melt during spring and early summer. The investigation shows the intensity of diurnal freeze-thaw cycles in the Antarctic to be one order of magnitude higher than in the Arctic. Moreover, the presented results clearly display that the occurrence of refreezing-events is subject to strong interannual variability in both hemispheres.