Analysis of characteristics and causes of extreme high temperature Analysis of characteristics and causes of extreme high temperature

During the summer of 2022, two periods of extreme high temperature events occurred in Chongqing. Using observations from 34 sites in the Chongqing and ERA5 reanalysis data, the main circulation anomalies during this period were analyzed. The results indicate that the strengthening and eastward extension of the South Asian High, along with the abnormal intensification and westward-northward extension of the Western Pacific Subtropical High (hereafter referred to as the Subtropical High), and the occurrence of an anomalously strong blocking high pressure north of the Sea of Japan extending to the Sea of Okhotsk (hereinafter referred to as the Okhotsk Blocking High), resulted in the stagnation of cold air above the 40°—50°N region, rendering it unable to influence the Yangtze River basin, including Chongqing. Chongqing was situated in a region of abnormally intense subsidence and moisture divergence under the western section of the Subtropical High, leading to persistent extreme high temperatures in the area. Analysis of the Subtropical High and South Asian High indices for different levels of regional high-temperature events since 2001 revealed that the Subtropical High extending westward to its most extreme position, while the center of the South Asian High was anomalously eastward in the summer of 2022. These factors directly contributed to Chongqing's extreme high temperatures. Additionally, the summer of 2022 witnessed anomalously warm sea surface temperatures in the western equatorial Pacific, with the average anomaly value in the 130°E—150°W, 30°—60°N region being the highest since 1961 for the same period, which strengthened the Okhotsk Blocking High. Under the influence of the La Niña event, Hadley circulation within the 110°—120°E range featured strong subsidence movements at 20°—30°N. This subsidence, combined with the central subsidence area of the Subtropical High, led to the abnormal intensification and westward extension of the Subtropical High, which in turn triggered the extreme high temperatures in Chongqing.