Precipitation Anomalies over the Qinghai–Xizang Plateau in Midsummer and Influences of the Bay of Bengal Cyclonic Vortex

Tropical cyclones (TCs) in the Bay of Bengal (BoB) significantly influence precipitation anomalies over the Qinghai–Xizang Plateau (QXP) in early summer and autumn. During midsummer (July–August), TCs rarely occur due to the strong environmental vertical wind shear, while cyclonic vortices (CVs) remain active over the BoB region. How midsummer CVs influence QXP rainfall remains poorly understood. This study investigates midsummer QXP precipitation anomalies and their linkage with BoB CVs based on daily precipitation data from 108 stations on the QXP and hourly ECMWF reanalysis 5 (ERA5) data with 0.25° resolution from 1980 to 2023. The results show that precipitation amount and intensity, extreme precipitation amount and frequency, and maximum daily precipitation amount in midsummer increase significantly in the northeastern QXP but decrease insignificantly in the Hengduan Mountains area. BoB CVs primarily occur in BoB coastal areas north of 15°N, presenting a deep vertical structure extending into the upper troposphere during midsummer. The CV frequency is positively (negatively) correlated with precipitation amount in the northeastern QXP (southern QXP), while its intensity shows a roughly opposite correlation pattern. In other words, QXP precipitation distribution patterns exhibit certain similarities between years with high (low) CV frequency and weak (strong) intensity. Composite analysis reveals that during high (low) CV frequency years, the vortex circulation extends northwestward (southeastward) to facilitate the transport of water vapor associated with the CV towards the northeastern (southern) QXP. During strong (weak) intensity years, the western Pacific subtropical high (WPSH) retreats eastward (extends westward), resulting in warm moist air related to the CV convergence over the southeastern QXP (northeastern QXP) region. This highlights the key role of BoB CVs in modulating QXP midsummer precipitation anomaly. The increasing (decreasing) trend in the CV frequency (intensity) from 1980 to 2023 may contribute to the abnormal increase in midsummer rainfall amount over the northeastern QXP.