Anomalously strong and stable maintenance of Western Pacific Subtropical High in the boreal summer of 2022 and the persistent extreme high temperature events in the middle and lower reaches of the Yangtze River

The strongest high-temperature event since 1960 occurred in the middle and lower reaches of the Yangtze River in the summer of 2022, and its formation and maintenance are related to the anomalous strong Western Pacific Subtropical High (WPSH). By using station observational data, reanalysis data, and diagnostic analysis of different variables, the manuscript investigated the mechanism of the anomalously strong and stable maintenance of the WPSH during the high temperature period. The results are as follows. (1) During the high temperature period, stronger sinking movements are prevalent in the middle and lower reaches of the Yangtze River compared to typical high temperature years, and the perturbation vertical dynamic heating term is the main factor for maintaining high temperatures in this region. Anomalous downward shortwave radiation flux can lead to transfer heat from the ground to the lower atmosphere through upward sensible heat flux, promoting surface heating. (2) Unlike typical high temperature years, the overlap of WPSH and South Asian High (SAH) facilitate the maintenance of WPSH over the middle and lower reaches of the Yangtze River, providing favorable circulation conditions for this extreme high temperature event. The maintenance of WPSH intensity was related to the local negative vorticity. One is the vertical downward transport of disturbance negative vorticity, and the other is the negative anomaly of relative vorticity horizontal advection. Especially, the vertical transport of negative vorticity from top to bottom plays a crucial role on maintaining WPSH over the middle and lower reaches of the Yangtze River. (3) Unlike typical high temperature years, the maintenance of the WPSH oceanic core was mainly related to the anomalously cold sea surface temperature near 180° around the equatorial central Pacific. The maintenance of the continental part of WPSH was closely related to convection near the Philippine Islands, which is beneficial for maintaining negative vorticity over the middle and lower reaches of the Yangtze River. The research results will deepen the understanding of the causes of WPSH variability, providing a theoretical basis for subsequent studies on the causes of persistent high temperatures.