The Extreme Hot Event Along the Yangtze Basins in August 2022

Abstract

Great part of China experiences hot spells in summer of 2022. In August, an extensive and intensive heat wave occurred along the Yangtze Basins, which persists nearly a month, causing serious damage and the worst summer drought, which is the second only to 2011. The persistent hot spell tends to be closely related with the anomalous activity of the Western Pacific subtropical high (WPSH). To better understand the causes, observations and reanalysis data are used to study the mechanism of anomalous activities of WPSH, the influence of tropical circulation, and the westerly long-wave trough ridge on WPSH.During summer of 2022, anomalous activity is observed in both the continental subtropical high and WPSH. In mid-late July, WPSH shifted to the west, and the continental subtropical high over the Iranian Plateau expanded to the east, resulting in the formation of a high-pressure belt and heat wave in the middle and the lower reaches of the Yangtze. In August, the continental subtropical weakens, and WPSH extended westward to 90°E, 40 longitudinal degrees to the west of its climatic position, which plays an important role in the persistent heat wave.The steady westward march of WPSH is discussed based on the investigation of both the anomalies of tropical circulation and systems in the westerlies. In August, the intertropical convergence zone over the region from the Western Pacific to South China Sea is intensified, associated with vigorous convection, and three typhoons or tropical cyclones. The remarkable local Hadley circulation appeared over the South China Sea, which supported the maintenance of WPSH to the west of 115°E.The flow pattern in the westerly zone also shows some particular features. From mean geopotential height field at 500 hPa for the hot spell, a pattern of "two ridges with a trough in between" maintains over the Eurasian region. The Okhotsk ridge in the east almost merges with WPSH into a stable high pressure dam. The Rossby wave activity indicates the ridge over the Ural area in the west consistently conveying energy southeastward, which also plays an important role in the strengthening and maintenance of the subtropical high.

Keywords

• hot spell
• the subtropical high
• tropical convection
• the westerly system