Analysis On Characteristics Of Extreme Temperature Days In China From 1961 To 2016 And Its Influencing Factors

Based on daily temperature and precipitation data of 760 stations in China during 1961-2016,this study adopted the percentage threshold method to define the extreme high temperature and extreme low temperature threshold for the temperature data in China from 1961 to 2016,and comprehensively analyzed the change trend,main change modes,periodic characteristics and mutation characteristics of extreme temperature days in summer and extreme low temperature days in winter,in addition,the correlation between precipitation and extreme temperature was studied.Based on the ERA-interim reanalysis data of global sea surface temperature,the study researched the key areas of global sea temperature that affect the extreme high temperature days in China and the extreme low temperature days in winter.Based on the NCEP/NCAR Reanalysis I Reanalysis data,the study analyzed the the correlations between different seasonal sea ice concentrations and the time coefficients of the first EOF modes for extreme temperature days in China,furthermore,the study researched the composited 2 m above ground temperature anomalies,composited surface pressure anomalies and composited 500 hPa geopotential height and wind anomalies,the intensity and position of the western Pacific subtropical high and the correlation coefficients between time coefficients of the first EOF modes for extreme temperature days and 200 hPa zonal wind,respectively.The main conclusions are as follows:(1)In addition to the third-step inland areas,the number of extremely high-temperature days in China has a significant increase trend.The trend of the number of extremely cold days in winter has shown a significant decrease trend across the country.The first three modes of EOF for summer extreme high temperature days in China showed the same changes in most parts of the country,the opposite changes in the south and the north,and the opposite changes in the southeastern coastal areas and areas between the Yangtze River and the Yellow River,areas in Liaoning and Jilin,their time coefficients were abruptly changed in 2002,1995,and 1978 respectively.The first three modes of EOF for winter extreme low temperature days in China showed the same changes across the country,the opposite changes in northeastern China and northern Xinjiang and the rest of the country,and the opposite changes in China's first ladder and second ladder,their time coefficients were abruptly changed in 1980,1982,and 1992 respectively.The time coefficients of the first three EOF modes for extreme temperature days in China have a period of change in the 3 or 4 year time scale that is tested by the significance of red noise.(2)The correlation between extreme high temperature days and precipitation in summer has a significant negative correlation across the country.The correlation between extreme winter days and precipitation in winter is not significant in most parts of the country,significantly negative correlations are mainly located in East China,while positively related regions are mainly located in western China.The SVD analysis of extreme temperature days and global sea surface temperature show that when the summer sea surface temperature is higher in equatorial western Pacific,the South Pacific,the Japan Sea,the Indian Ocean,the western North Atlantic and the North Sea,or the winter sea surface temperature is lower in the sea near Antarctica,the northeastern corner of Greenland to Sval,the summer extreme high temperature days in most parts of China will be more,while the increase in southern China and northwest China will be more pronounced.When the winter sea surface temperature in the northern part of the central equatorial Pacific,the Sargassum sea area in the western North Atlantic,and the Arabian Sea in the Indian Ocean is higher in the winter,the overall number of winter extreme cold days in China will be less.(3)In the early period autumn to the same period summer,the sea ice concentration in the Arctic Ocean have significant negative correlations with the time coefficient of the first EOF mode for summer extreme high temperature days in China.In the early period autumn to the same period summer,the sea ice concentration near the Antarctica and the time coefficient of the first EOF mode for summer extreme high temperature days in China have significantly positive correlation areas that are distributed sporadically in the Indian Ocean basin,the Pacific Antarctic Ridge area,and the north of the Enderby area.There are significant positive correlations between the sea ice concentration in the Arctic Ocean and the time coefficient of the first EOF mode for winter extreme low temperature days in the four seasons of the same season from the same period spring to the same period winter.The significant positive correlation areas in the same period spring and the same period winter are small.The positive correlation area in the same period summer is similar to the same period in the autumn,but it is larger than the significant positive correlation area in the the same period autumn.The time coefficient of the first EOF mode for winter extreme low temperature days is mainly negatively correlated with the sea ice concentration in the southern hemisphere in the four same period seasons.(4)These anomalies in summer will be conducive to the extreme high temperature days in China,the Arctic polar and Antarctic seas have an abnormally high temperature of 2 meters on the ground and the ground pressure is abnormally weakened,the intensity of the western Pacific subtropical high is strong,the subtropical ridge points are west and north,and the 500 hPa geopotential height in the northern Europe,the North Pacific Aleutian Islands and the Antarctic center increases abnormally,the 500 hPa geopotential height in Bielins near Antarctica,the Gaojinhai,Southwest Indian and Auckland Islands weakens abnormally,and the 200 hPa zonal wind anomaly weakens from the Tibetan Plateau to the East China Sea.These anomalies in winter will be conducive to the extreme low temperature days in China,The Arctic Polarity,the waters near the Svalbard Islands in the east of Greenland,and the Central Siberian region have an abnormally low temperature of 2 meters,the surface pressure in the Arctic Ocean and the east of Greenland and the Siberian High are abnormally enhanced,the maximum positive anomaly is over 5hPa in Europe,the northern ground pressure and the Aleutian depression weakened abnormally,and the 500 hPa geopotential increased abnormally in the high latitude area over the northern hemisphere,especially over southern Greenland and the Ural Mountains,the 500 hPa geopotential height decreased abnormally in the middle and low latitudes,especially in the eastern part of North America,western Europe and Inner Mongolia,Antarctica,and Beilings,the geopotential height at 500 hPa in the middle and low latitudes of the Southern Hemisphere increased abnormally,and the western Pacific subtropical area decreased,the high-pressure intensity is weak,the subtropical high 588 line disappears,the 200 hPa westerly over the Tibetan Plateau to the East China Sea increases abnormally,and the 200 hPa latitudinal westerly over the mid-high latitudes of Asia weakens abnormally.