Why was the heat wave in the Yangtze River valley abnormally intensified in late summer 2022?

Abstract

A record-breaking heat wave hit the Yangtze River valley during the boreal summer of 2022, and caused severe social and economic losses. One prominent feature of this long-lived heat event was its persistence and abnormal intensification in August. This study investigated the physical mechanisms be responsible for the intensification of this heat event in late summer under the background of a La Niña event. The prolonged heat event was directly related to the intensification and westward extension of the western North Pacific subtropical high (WNPSH), which can be attributed to the synergistic effects of an anomalous western North Pacific (WNP) anticyclone and the eastward extension of the South Asian high (SAH) in the upper troposphere. The anomalous anticyclone in the WNP, which was induced by negative sea surface temperature anomalies in the central tropical Pacific, strengthened in August. The positive sea surface temperature anomaly in the western Pacific warm pool and enhanced in-situ convection led to anomalous high pressure over the Yangtze River valley via the local meridional circulation. Atmospheric convergence and descending motion over the Yangtze River valley was amplified in August as a result of the zonal shift in the SAH from the Iranian Plateau to the Tibetan Plateau. The Silk Road pattern (SRP) index of August 2022 was the lowest since the 1990s. The abnormal negative phase of the SRP contributed to both the zonal shift in the SAH and the westward extension of the WNPSH, which led to the abnormal intensification of the heat event over the Yangtze River valley in August 2022.