An update to the Arctic Ocean snow melt onset data set

The discussion of global warming in recent decades has caused increased interest in year-to-year climate variations in the polar regions. The sensitivity of the polar regions to climate variations and change is believed to result from the complex exchange mechanisms operating between the oceans, ice and atmospheric systems. The significance of sea ice in the polar regions is particularly emphasized during the spring transition period from winter to summer conditions. This study presents an update to the snow melt onset data set, which is generated for Arctic sea ice surfaces using 25 km2 daily-averaged brightness temperatures from the Scanning Multichannel Microwave Radiometer (SMMR) and the Special Sensor Microwave/Imager (SSM/I) sensors. The advanced horizontal range algorithm (AHRA) utilizes temporal information in the brightness temperature difference between 19GHz (18GHz for SMMR) and 37GHz to determine melt onset over sea ice locations in the Arctic. The melt onset dates are generated annually from1979 through 2002, and are available via ftp from the National Snow and Ice Data Center (NSIDC). The results show snow melt onset begins in the Bering Sea and Sea of Okhotsk in the first week of March, and progressed northward towards the central Arctic by the middle of July. The latest melt onset dates were observed in the Lincoln Sea, north of Greenland, in accordance with the minimum in air temperatures located over Greenland. In comparison with the roughly radial northward melt progression of the annually averaged melt onset map, specific years showed a high degree of spatial variability. Most years typically have some regions of earlier than average melt, and other regions with later than average melt. However, 1990 appeared to be an extraordinarily early melt onset year, with later than average snow melt onset predominately occurring in the Beaufort Sea. There is considerable opportunity to use this new melt onset data set for climate studies, including the development and validation of general circulation model outputs, and for the detection of climate change.