Climatic Division And Extreme Cooling Events Based On The Minimum Daily Temperature In Winter Half Year In Mainland China

Based on the daily minimum temperature data of 2474 stations in China from 1960 to 2015,56 winter half years are selected,and NCEP / NCAR reanalysis data set is used.Using REOF,synthetic analysis and percentile method,we have systematically investigated the climatic division and extreme cooling events in winter half year in mainland China.The main conclusions are as follows:(1)The average lowest temperature in winter half year in China was different in spatial distribution.The standard deviation of the lowest temperature also has spatial difference in spatial distribution.The interannual variation of mean daily minimum temperature in winter half year in China varies with different regions.China is divided into seven regions by REOF method.In the seven regions,there are significant differences in the change of the minimum temperature.There are multiple time scales in the change of the minimum temperature.In addition to the uniform warming,there are also obvious interdecadal changes of about 10 a cycle.On the interannual time scale,except for the southern region,there are some periodic changes.(2)When extreme low temperature events occur in 7 regions of the mainland of China,the wind direction of each layer of troposphere is different.The vertical structure of circulation in different regions is different,showing the characteristics of barotropic and baroclinic.When the low temperature abnormal events occur,there is an anticyclone center in the middle and high latitude area,which mainly moves in the east-west direction near 60 ° N;there is a large area of cyclonic circulation over the abnormal areas.There are also regional differences in the propagation of disturbance energy,which can be divided into the South Branch westerlies and the mid latitude westerlies.When the low temperature anomaly occurs,the pressure distribution in some areas also shows the basic structural characteristics of AO.(3)According to the above conclusions,China is divided into seven regions,By averaging the cooling thresholds of all stations in each region,seven cooling thresholds are obtained.The cooling extremes(CE)are defined and the temporal and spatial features of extreme cooling events in winter half year are studied.There are significant spatial differences in the frequency distribution of extreme cooling events in winter half of China.In the past 56 years,the frequency of CE has shown an interannual and interdecadal fluctuation.The spatial distribution of the frequency in different years is basically the same,and the trend changes show different characteristics.In recent years,the frequency in each region tends to be stable,and the variation rate is significantly reduced compared with that before mutation.The mutation time of each region is different.The trend of monthly frequency of CE is not the same.