Characteristics And Possible Causes Of Wintertime Large-scale Extreme Cold And Warm Days Over China

The extreme changes of winter temperature often have a great impact on people's production and life,and also cause losses to the national economy.Based on daily surface air temperature observations from National Meteorological Information Center and Japanese 55-year Reanalysis(JRA-55)from Japan Meteorological Agency,this study investigats the characteristics and changes of wintertime extreme cold and warm days of consistent pattern and anti-phase pattern between north and south over China from 1961 to 2017,and further discusses the factors that may affect them.The results show that during the winter of 1961-2017,the frequency of extreme cold and warm days of consistent pattern and anti-phase pattern between north and south show obvious interdecadal variation trend.With the increase of average temperature in China,the number of consistent extreme cold days is decreasing,the number of consistent extreme cold days is decreasing,and the occurrence time tends to be concentrated in period between late December and early January,while consistent extreme warm days are significantly increased in January and February.The variations of the extreme cold and warm days anti-phase pattern between north and south basically present the opposite trend,the number of extreme southern warm and northern cold days was less from 1980 s to mid-1990 s,but increased after 2000.However,the number of extreme southern cold and northern warm days increased significantly after 1980 s,and decreased after 2000.Through further research and analysis,it is preliminarily considered that global warming causes the increase of consistent extreme warm days and the decrease of consistent extreme cold days,however,it has little effect on the total days of the extreme cold and warm days of consistent pattern and the north-south anti-phase type of extreme cold and warm days.The intensity of Siberian high may be the main influencing factor of the total occurrence days of consistent extreme cold and warm days.The weakening(strengthening)of the Siberian high intensity before(after)the1990s corresponds to the decreasing(increasing)of the total days of the consistent extreme cold and warm days.For the north-south anti-phase type of extreme cold and warm days,the extreme southern cold and northern warm days and the extreme southern warm and northern cold days basically present the characteristics of reverse phase change,which may be related to the north-south distribution of the Siberian high.When the center of the Siberian high is in the middle and high latitudes,the extreme southern warm(cold)and northern cold(warm)days are more(less),while when the north-south difference of the Siberian high intensity is small,the extreme southern cold(warm)and northern warm(cold)days are more(less).In addition,the total number of extreme cold and warm days of the north-south antiphase type changed little during the winter of 1961-2017,the North Atlantic Meridional Overturning Circulation(AMOC)may be the driving factor of the changes in the total number of days of two types of wintertime large-scale extreme cold and warm days in China.