摘要
Extreme temperature events can influence the natural environment and societal activities more so than mean temperature events. This study used daily data from 238 stations north of 60°N, obtained from the Global Summary of the Day dataset for the period 1979~015, to investigate the trends of summertime extreme temperature. The results revealed most stations north of 60°N with trends of decrease in the number of cold days （nights） and increase in the number of warm clays （nights）. The regional average results showed trends of consistent decline （rise） of cold days and nights （warm days and nights） in Eurasia and Greenland. Similarly, the trends of the seasonal maximum and minimum values were most significant in these regions. In summer, of three indices considered （i.e., Arctic Oscillation, Arctic dipole, and E1 Nifi^Southem Oscillation）, the largest contributor to the trends of extreme temperature events was the Arctic dipole. Prevailing southerly winds in summer brought warm moist air across northern Eurasia and Greenland, conducive to increased numbers of warm days （nights） and decreased numbers of cold day （nights）. Moreover, we defined extreme events using different thresholds and found the spatial distributions of the trends were similar.
Extreme temperature events can influence the natural environment and societal activities more so than mean temperature events. This study used daily data from 238 stations north of 60°N, obtained from the Global Summary of the Day dataset for the period 1979~015, to investigate the trends of summertime extreme temperature. The results revealed most stations north of 60°N with trends of decrease in the number of cold days （nights） and increase in the number of warm clays （nights）. The regional average results showed trends of consistent decline （rise） of cold days and nights （warm days and nights） in Eurasia and Greenland. Similarly, the trends of the seasonal maximum and minimum values were most significant in these regions. In summer, of three indices considered （i.e., Arctic Oscillation, Arctic dipole, and E1 Nifi^Southem Oscillation）, the largest contributor to the trends of extreme temperature events was the Arctic dipole. Prevailing southerly winds in summer brought warm moist air across northern Eurasia and Greenland, conducive to increased numbers of warm days （nights） and decreased numbers of cold day （nights）. Moreover, we defined extreme events using different thresholds and found the spatial distributions of the trends were similar.
基金
supported by National Key R&D Program of China (Grant no.2017YFE0111700)
Beijing Municipal Natural Science Foundation (Grant no.8182023)
