The extreme heat wave in China in August 2022 related to extreme northward movement of the eastern center of SAH

Abstract

This study reveals the causes of extreme high temperatures in China in August 2022 and the role of South Asian high (SAH) anomaly. The 2022 extreme heat events in the Tibetan Plateau (TP) and Yangtze River basin (YRB) are the strongest since 1979, accompanied by an anticyclonic anomaly in the northeastern part of the SAH. Six displacement indices of the SAH are defined by taking advantage of the stream function R of horizontal circulation in the three-pattern decomposition of the global atmospheric circulation (3P-DGAC) model, which can effectively remove the systematic errors in geopotential high caused by global warming. The results show an extreme northward shift of the eastern center of SAH occur in August 2022, with correlation coefficients 0.85 and 0.69 with the temperature anomaly indices of TP and YRB regions, respectively, for 1979–2022. In addition to the La Niña event, we find evidence that the soil moisture in the Indo-China Peninsula (ICP) region from January to August 2022 is extremely wet, linked to significant impacts on the northward movement of the eastern center of SAH response to land-air interactions. Further, the 3P-DGAC model helps us to reveal that the extreme northward shift of the eastern center of SAH brings extensive circulation adjustments, in which the local meridional circulation anomaly intensifies the high temperature in the YRB, while the local zonal circulation in the middle latitudes is the main cause of the high temperature in the TP. Meanwhile, the northward shift of the eastern center of SAH pushes the East Asian subtropical westerly jet (EAJ) northeastward, and the convergent downdraft to the right of EAJ exit also further aggravates the summer hot extremes in China in 2022.