A multi-data set analysis of variability and change in Arctic spring snow cover extent, 1967-2008

A new multi-data set estimate of Arctic monthly snow cover extent ( SCE) in the May-June melt period is derived from 10 data sources covering different time periods from 1967 to 2008. The data sources include visible and microwave satellite observations, objective analyses of surface snow depth observations, reconstructed snow cover from daily temperature and precipitation, and proxy information derived from thaw dates. The new estimates show a more linear reduction in spring SCE than previously characterized by the National Oceanic and Atmospheric Administration weekly snow chart data set, with air temperature explaining 49% of the variability in Arctic SCE in May and 56% of the variability in June. The Arctic Oscillation is only significantly linked to Arctic SCE in May where it explains 25% of the variance in Eurasian sector SCE. Trend analysis of the multi-data set series ( including an annually varying estimate of error) reveals that May and June SCE have decreased 14% and 46%, respectively, over the pan-Arctic region over the 1967-2008 period in response to earlier snow melt. These results are confirmed with in situ data from Canada, Alaska and Russia that show significant reductions in spring snow cover duration over the last 30 years. The spring snow cover temperature sensitivity over the pan-Arctic region during this period is estimated to be in the range -0.8 to -1.00 x 10(6) km(2) degrees C-1. The observed reductions in June SCE over the 1979-2008 period are found to be of the same magnitude as reductions in June sea ice extent with both series significantly correlated to air temperature changes over the Arctic region and to each other. This result underscores the close relationship between the cryosphere and surface air temperatures over the Arctic region in June when albedo feedback potential is at a maximum.