| Summary: | The snow melt onset date represents an important transitional point in the Arctic energy balance, when the surface albedo decreases rapidly and surface energy absorption increases rapidly in response to the appearance of liquid water. An improved understanding of the spatial and temporal variability of melt onset is valuable for climate change detection, climate simulations, and model validation in the Arctic region. Passive microwave satellite data are indispensable in this task because they are relatively unaffected by cloud cover, not reliant on solar illumination, and have relatively high repeat coverage capabilities. In this study, snow melt onset dates are derived for 1979–1998 using horizontal polarizations at 18 and 37 GHz from the Scanning Multichannel Microwave Radiometer (SMMR) and 19 and 37 GHz from the Special Sensor Microwave/Imager (SSM/I) sensors. Trends towards earlier snow melt onset occur from 1979–1998 throughout much of the western Arctic, including areas of the Laptev, East Siberian, and Beaufort Seas. Correlation and principal component analyses further suggest significant spatial variability exists in the melt onset dates between geographic areas located approximately 180° of longitude apart. The underlying cause of the variations in the snow melt onset date over sea ice is a combination of high-frequency synoptic events and the larger atmospheric patterns, described by teleconnection indices, within which they occur. For instance, day to day variations in near surface air temperature and surface longwave radiation flux over two case study regions related to the progression of melt onset. On an annual time scale, positive phases of the Arctic Oscillation (AO) are related to earlier than average melt onset dates in the Kara, Laptev, and East Siberian Seas, the Canadian Arctic Archipelago, and western portions of the Arctic Ocean, but are related to delayed melt onset in Baffin Bay. Positive phases of the North Pacific (NP) pattern are also related to earlier than average melt onset in ...
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