The Spatial And Temporal Characteristics And Causes Of The Frequency Of Warm Winter Days In China From 1951 To 2014 And Comparative Analysis Around Global Warming Stagnation

In this paper,the frequency of warm winter days(FWWD)in China(the number of days that high temperature lasts over 6 days)was defined using the observed daily maximum near-surface temperature of HadGHCND from Hadley centre in the UK,and then its variation during the full time(1951-2014)?before(1951-1997)and after(1998-2014)the global warming stagnates were discussed.After that,we analyzed the relationship between atmospheric circulation anomalies?SST(sea surface temperature)anomalies Qinghai-Tibet Plateau snow cover anomalies ?monsoon anomalies and FWWD in China.The main conclusions are as follows:(1)The first FWWD EOF(1951-2014)is a uniform variation pattern,with the maximum mainly located between the north of Yangtze River and north China,and the minimum mainly located in the Qinghai-Tibet Plateau.When the FWWD increases uniformly,the geopotential height shows a dipole distribution with positive and negative anomaly overlying the middle and high latitudes in the eastern hemisphere.The spatial distribution of first FWWD pattern after global warming stagnates is more similar to the full time period(their correlation coefficient were 0.86).The difference is that there were fewer FWWD on Qinghai-Tibet Plateau after the global warming stagnates.Although the FWWD's pattern before the global warming stagnates is still a uniform variation pattern,it's maximum mainly located in the Sichuan Basin in central China.(2)The second FWWD EOF(1951-2014)is a asymmetric pattern of north-south out of phase,with the maximum located at the steep slope in the southeast of the Qinghai-Tibetan Plateau.When the FWWD is less in the north and more in the south in China,the geopotential height anomalies are arranged orderly as “+-+” southward from the pole.This distribution is similar to the combination of Arctic Oscillation(AO)and Western Pacific teleconnection pattern.The spatial distribution of second FWWD pattern before global warming stagnates is more similar to the full time period(their correlation coefficient were 0.96),it's geopotential height anomalies were still similar to the anti-phase of AO pattern.After the global wormingstagnates,the second FWWD's EOF is quiet different,it's maximum mainly located near the Qinghai-Tibet Plateau,and the boundary between positive and negative FWWD is near 40°N.The negative FWWD mainly concentrated in the northeastern region north of 40°N.(3)The anomalous warm SSTA in China's adjacent sea and warm tongue in the Kuroshio extension area are closely related to the above two main patterns.In addition,ENSO has a predictive effect on the second FWWD's patter after global warming stagnates.(4)The first pattern of FWWD in China has a good correlation with the Qinghai-Tibet plateau winter wind intensity index,which indicates that TP winter monsoon is one of the factors affecting the FWWD around the TP region.Meanwhile,the snow cover rate underlying TP region has a predictive effect on the variation in the both FWWD's pattern after global worming stagnates.