2022年8月长江流域持续性极端高温事件成因

The Extreme Hot Event Along the Yangtze Basins in August 2022

2022年夏季长江流域经历了罕见的高温酷暑天气。2022年8月高温区几乎覆盖整个长江流域,形成全流域型高温,并持续近1个月。持续高温与西北太平洋副热带高压(简称副高)的异常活动关系密切。8月副高西伸且稳定,其西端脊点到达90°E,比常年偏西近40个经度,控制了几乎整个长江流域,引起罕见的持续高温。导致副高稳定西伸的重要原因如下:热带环流的异常从南面支持副高的维持;8月西太平洋至南海地区赤道辐合带持续偏强,对流明显偏强;南海地区出现明显增强的Hadley环流,支持115°E以西副高的维持。此外,西风带环流的异常分布有利于副高西伸;欧亚地区500 hPa位势高度场上维持两脊一槽的形势,鄂霍次克海高压脊几乎与副高打通,形成稳定的高压坝;乌拉尔地区的高压脊不断向东南方向输送Rossby波能量,也对副高西段的维持和加强起重要作用。

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.