A Study Of The Summer Temperature Characteristics And Its Atmospheric Circulation Cause In Jianghuai Region

Under the influence of global climate change,the occurrence of extreme weather is increasing,which has many adverse effects on people’s life,crop growth,energy utilization,economic development and ecological environment.Based on ERA5 daily and monthly mean temperature data,the variation characteristics of summer temperature in Jianghuai Region were studied and the typical high temperature and low temperature years were defined.Then,the characteristics of atmospheric circulation in high temperature and low temperature years were compared from the perspective of various atmospheric circulation factors.On this basis,the relationship between summer high temperature in Jianghuai Region and Western Pacific Subtropical High(WPSH)and large scale teleconnection type is analyzed.Finally,a case study was conducted in the summer of 2018 to understand the development process of a specific anomalous high temperature and the cause of circulation.The main results are as follows:(1)From 1980 to 2019,the summer air temperature in the Jianghuai Region showed a fluctuating trend of increase,with alternating cold and warm.Before 2000,the overall air temperature was low,and then increased rapidly.In recent 10 years,except 2014 and 2015,the air temperature was above the average.The mean temperature increased by 0.63 ℃ after the abrupt change in 2000.And the spatial distribution is consistent,and the summer temperature in the whole Jianghuai Region shows an increasing trend.The variation of summer temperature in Jianghuai Region of China is mainly influenced by WPSH,East Asian summer monsoon and Siberian cold air.(2)During the high temperature years,there is a strong negative anomaly in the Jianghuai Region and a large positive anomaly in the Pacific Ocean,and the East Asian summer monsoon strengthens.In 500 h Pa height field,Jianghuai Region,north Korea,near the sea of Japan to the north Pacific are wide range of geopotential height anomaly area,western Pacific subtropical high overall strong and north,the Jianghuai Region is located near the ridge line of the WPSH,and the region was controlled by anticyclonic circulation in the wind field of 850 h Pa and 200 h Pa,subtropical westerly jet strong,there are deep anomalous anticyclonic circulation and subsidence movement in the whole troposphere,which has important influence on the generation and maintenance of high temperature.In low temperature years,the Jianghuai Region is a strong negative anomaly area of sea level pressure anomaly and the intensity of East Asian summer monsoon is weak.In 500 h Pa height field,the Jianghuai Region,the Korean Peninsula and the Sea of Japan are controlled by the negative anomaly of geopotential height anomaly,and the WPSH intensity is weak.The Jianghuai Region is on the north side of the WPSH ridge line.In the 850 h Pa wind field,the region is controlled by cyclonic circulation,and the upper subtropical westerly jet is weak.In addition,the anomalous change of SST over the equatorial Middle East Pacific will cause the change of summer air temperature over the Jianghuai Region.In high temperature years,the equatorial Middle Eastern Pacific region is controlled by negative SST anomaly,while the western Pacific and the Sea of Japan have obvious positive SST anomaly,which has the characteristics of La Nina events.In low temperature years,there is a significant positive SST anomaly in the equatorial Middle East Pacific,while the west Pacific and the Sea of Japan are controlled by negative SST anomaly,which has the characteristics of El Nino events.(3)Number of summer high temperature days in the Jianghuai Region and the WPSH strength,area,ridge line position index are positively correlated,and negatively correlated with the west stretched ridge point index.The correlation between high temperature days and the WPSH intensity,area,western ridge point index is more significant in the eastern coastal area,the correlation coefficient absolute value of 0.5or so,and the correlation with ridge line index is more significant in the northern Jianghuai region.In addition,SVD analysis of the anisotropic correlation between500 h Pa average geopotential height field and high temperature days shows that the variance contribution of the first mode reaches 84.4%,and the correlation coefficient is0.71.Combines with the distribution of the anisotropic correlation coefficient of the first mode and the corresponding time series,when the geopotential height field of500 h Pa at middle and low latitudes is strong,abnormal high temperature days tend to occur in summer in the Jianghuai Region.On the contrary,abnormal high temperature days are rare.(4)The correlation between high temperature days and PJ index,WP index is 0.36and-0.35,respectively.The distribution of the correlation coefficient with PJ index is high in the north and low in the south.The correlation coefficient in the north of 31°N was above 0.3 and passed the significance test of 0.05.The most obvious correlation coefficient is in the north of Anhui province and Jiangsu Province,and the correlation coefficient is over 0.42.The significant correlation with WP index is mainly in some regions of Jiangxi,Henan and the eastern coastal areas,with negative correlation coefficient of-0.4.In Wenzhou and Taizhou of Zhejiang province,the correlation coefficient with absolute value of more than 0.5,is-0.54 and-0.52,respectively.In addition,the distribution characteristics of 500 h Pa mean geopotential height field in positive and negative years of PJ index and WP index also indicate that PJ and WP teleconnection type has certain influence on summer high temperature anomalies in the Jianghuai Region.(5)Through the analysis of summer high temperature in the Jianghuai Region in2018,it can be concluded that there are few abnormal high temperature days in June,and the abnormal high temperature days mainly occur in July and August.Moreover,there are obvious spatial differences in abnormal high temperature,showing the overall distribution pattern of high in the south and low in the north.In addition,the 500 h Pa average geopotential height field of the high temperature process in four stages is analyzed.In general,the WPSH is located in the north,the area is larger,and the Jianghuai Region is in its control area,which is more conducive to the enhancement and maintenance of the high temperature process.