The anomalously strong and persistent western Pacific subtropical high in summer 2022 in association with the extreme heatwaves 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 anomalously strong Western Pacific Subtropical High (WPSH). Using station observational data, reanalysis data, and diagnostic analysis of different variables, the present study investigates the mechanism for the anomalously strong and stable maintenance of the WPSH during the high temperature period. 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 that in 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 heat transfer from the ground to the lower atmosphere through upward sensible heat flux, promoting surface heating. (2) Unlike the situation in the typical high temperature years, the overlap of WPSH and South Asian High (SAH) in the summer of 2022 facilitated the maintenance of WPSH over the middle and lower reaches of the Yangtze river, providing a favorable circulation condition for the extreme high temperature event. The maintenance of WPSH intensity was related to local negative vorticity, i.e., the downward transport of negative vorticity disturbance and the negative anomaly of horizontal advection of relative vorticity. Especially, the vertical transport of negative vorticity from top to bottom played a crucial role on maintaining the WPSH over the middle and lower reaches of the Yangtze river. (3) Unlike that in typical high temperature years, the maintenance of the WPSH oceanic core was mainly related to anomalously low sea surface temperature near 180° around the equatorial central Pacific. The maintenance of the continental part of the WPSH was closely related to convection near the Philippine Islands, which was favorable for maintaining negative vorticity over the middle and lower reaches of the Yangtze river. The research results will deepen our understanding of the causes of WPSH variability and provide a theoretical basis for subsequent studies on the causes of persistent high temperature.