Midsummer high temperature types in southern China and corresponding large-scale circulation and sea surface temperature anomalies

KeyWord:Midsummer high temperature;Clustering analysis;Atmospheric circulation;Sea surface temperature anomaly

Abstract:

      Daily maximum temperature data collected at 2374 stations in China, the NCEP/NCAR atmospheric circulation data and NOAA sea surface temperature (SST) data are used to analyze the main types of midsummer high temperature in the southern China. Large-scale circulations corresponding to these high temperature types and their relation with SST anomalies are explored. The results show that the annual high temperature days in the southern China has a significant increasing trend. Cluster analysis is used to classify the midsummer high temperature in the southern China into three types: Jianghuai type, South China type and Central China type. The Jianghuai type high temperature is centered in the Jianghuai area, with a wide range and high occurrence frequency. When the Jianghuai type high temperature occurs, anomalous anticyclone occurs in the troposphere from low to high levels. Meanwhile, the Western Pacific subtropical high (WPSH) is stronger than normal and shifts to the west with the ridgeline located slightly northward. Therefore, Jianghuai type high temperature is a high temperature type under the control of the WPSH. This type of high temperature is mainly related to the attenuation of the central type El Niño from the pre-winter to the subsequent summer and warmer SST in the equatorial Atlantic in spring. The central area of South China type high temperature occurs from the southern Yangtze River basin to South China. The typical circulation systems are the southward displacement of the East Asian subtropical jet, the stronger and westward shift of the WPSH with a southward shift of the ridgeline. Also, the South China type high temperature is directly under the control of the WPSH, accompanied by a weakened southwesterly monsoon circulation. It has an obvious characteristic of dry heat. This type of high temperature is closely related to the attenuation of the eastern type El Niño and its associated Indian Ocean capacitor effect. The Central China type high temperature is mainly located in Hubei province and Hunan province. The corresponding circulation is that the WPSH is slightly weaker and shifts eastward, which shows a similar pattern to the North Atlantic-Eurasia remote correlation pattern in the middle and high latitudes. It is the high temperature under the control of continental high pressure, which makes the water vapor condition better than the other two types of high temperature. The North Atlantic-Eurasian teleconnection is a possible signal source of Central China type high temperature.