The atmospheric circulation anomalies and impact mechanisms of the extreme heat and drought event over Yangtze River Basin in 2022

In the midsummer of 2022, an extreme compound event of high temperature and drought, historically rare, occurred in the Yangtze River Basin. Investigating its causes and impact mechanisms is of great significance for the scientific understanding of extreme climate events. This study utilizes data such as the daily maximum temperature observation data from 720 national meteorological stations across the Yangtze River Basin, the meteorological draught composite index (MCI), and the NCEP/NCAR reanalysis data to systematically analyze the atmospheric circulation anomalies and the influence mechanisms of sea surface temperature (SST) external forcing. The results indicate that during the summer of 2022, the Western Pacific Subtropical High (WPSH) and South Asian High (SAH) exhibited unprecedented intensification and dominated the Yangtze River Basin, with their intensities reaching historical extremes. An abnormally northward 200 hPa subtropical westerly jet (SWJ) formed a warm ridge, effectively blocking the convergence of cold and warm air masses. The Yangtze River Basin was controlled by an anomalous anticyclonic circulation, leading to significant water vapor divergence. The re-intensification of the La Ni?a event and the record-breaking strengthening of the negative phase of the Tropical Indian Ocean Dipole (TIOD) worked synergistically to enhance the descending branches of both the Walker and Hadley circulations. Under the guidance of the subtropical westerly jet, this further reinforced the deep high-pressure system over the Yangtze River Basin, ultimately resulting in the prolonged extreme high temperature and drought event. Notably, against the backdrop of global warming, the interdecadal warming of the Indian Ocean Warm Pool (IOWP) and the Western Pacific Warm Pool (WPWP) has led to increasingly significant impacts of their anomalously warm SSTs on the WPSH and SAH. These influences have now surpassed those of SST anomalies in the equatorial central-eastern Pacific, making them crucial predictors for sub-seasonal to seasonal forecasting.