Spatio-temporal analysis of the melt onset dates over Arctic sea ice from 1979 to 2017

The melt onset dates(MOD) over Arctic sea ice plays an important role in the seasonal cycle of sea ice surface properties, which impacts Arctic surface solar radiation absorbed by the ice-ocean system. Monitoring interannual variations in MOD is valuable for understanding climate change. In this study, we investigated the spatio-temporal variability of MOD over Arctic sea ice and 14 Arctic sub-regions in the period of 1979 to 2017 from passive microwave satellite data. A set of mathematical and statistical methods, including the Sen’s slope and Mann-Kendall mutation tests, were used to comprehensively assess the variation trend and abrupt points of MOD during the past 39 years for different Arctic sub-regions. Additionally, the correlation between Arctic Oscillation(AO) and MOD was analyzed. The results indicate that:(1) all Arctic sub-regions show a trend toward earlier MOD except the Bering Sea and St. Lawrence Gulf. The East Siberian Sea exhibits a significantly earlier trend, with the highest rate of-9.45 d/decade;(2) the temporal variability and statistical significance of MOD trend exhibit large interannual differences with different time windows for most regions in the Arctic;(3) during the past 39 years, the MOD changed abruptly in different years for different sub-regions;(4) the seasonal AO has more influence on MOD than monthly AO. The findings in this study can improve our knowledge of MOD changes and are beneficial for further Arctic climate change study.