Investigation of Arctic air temperature extremes at north of 60°N in winter

Air temperature is a key index reflecting climate change. Air temperature extremes are very important because they strongly influence the natural environment and societal activities. The Arctic air temperature extremes north of 60°N are investigated in the winter. Daily data from 238 stations at north of 60°N from the global summary of the day for the period 1979–2015 are used to study the trends of cold days, cold nights, warm days and warm nights during the wintertime. The results show a decreasing trend of cold days and nights（rate of –0.2 to –0.3 d/a） and an increasing trend of warm days and nights（rate of ＋0.2 to ＋0.3 d/a） in the Arctic. The mean temperature increases,which contributes to the increasing（decreasing） occurrence of warm（cold） days and nights. On the other hand,the variance at most stations decreased, leading to a reduced number of cold events. A positive AO（Arctic Oscillation） index leads to an increased（decreased） number of warm（cold） days and nights over northern Europe and western Russia and an increased（decreased） number of cold（warm） days and nights over the Bering Strait and Greenland. The lower extent of Arctic autumn sea ice leads to a decreased number of cold days and nights.The occurrences of abrupt changes are detected using the Mann-Kendall method for cold nights occurring in Canada in 1998 and for warm nights occurring in northwestern Eurasia in 1988. This abrupt change mainly resulted from the mean warming induced by south winds and an increased North Atlantic sea surface temperature.