Links Between The Synergistic Effect Of High-latitude Blocking In Northern Hemisphere Winter And Extreme Cold Events In China

The extreme cold events in China have shown a gradual increase since 2004 under climate warming,which has had a major impact on Chinese social and economic development and people's normal life.Researching and improving the driving factors and physical mechanisms of extreme cold events under the background of warm winter can effectively improve people's resistance to climate change.Based on the monthly mean and daily CMA stations,ERA-interim reanalysis,NCEP/NOAA reanalysis and Had GEM3-GA6 model datasets,this study investigated the driving mechanism of the extreme cold events in China under climate warming via a new perspective on the high-latitude concurrent blocking.Results show that:(1)Extreme cold events have increased in China corresponding on more frequent high-latitude concurrent blocking since 2004.This synergistic effect of high latitude blocking is closely related to extreme cold events in the mid-latitudes.(2)The enhanced high-latitude concurrent blocking under climate warming can strengthen the "warm Arctic-Cold Eurasian" mode by stimulating abnormal high pressures in the lower and middle Arctic troposphere.(3)The high-latitude concurrent blocking can predict extreme cold events in China about 10-20 days ahead by accelerating the Arctic Oscillation(AO)phase transition,changing the intensity and position of the Polar Vortex.(4)Human activities have two sides to extreme cold events.The direct thermal effect of human activities will weaken the extreme cold events,but the indirect dynamic effect of human activities will indirectly strengthen the extreme cold events by strengthening the high-latitude concurrent blocking.Due to the direct thermodynamical weakening effect was dominant,human activities eventually led to the weakening of extreme cold events in China.