Precipitation Anomalies over the Tibetan Plateau in Midsummer and the Influence of Bay of Bengal Cyclonic Vortex

Tropical cyclones (TCs) in the Bay of Bengal (BoB) significantly influence precipitation anomalies over the Tibetan Plateau (TP) in early summer and the autumn. During midsummer (July-August), TCs rarely occur due to the stronger environmental vertical wind shear, while cyclonic vortices (CVs) still remain active over the BoB region. This study investigates midsummer TP precipitation anomalies and their linkage with BoB CVs based on daily precipitation data from 108 stations on the TP and hourly ECMWF reanalysis 5 data with 0.25°resolution from 1980 to 2023. Results show that precipitation amount and intensity, extreme precipitation amount and frequency, and maximum daily precipitation amount in midsummer increase significantly in the northeastern TP 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 TP (southern TP), while its intensity shows a roughly opposite correlation pattern. Therefore, TP 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) TP. 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 TP (northeastern TP) region. This highlights the key role of BoB CVs in modulating TP midsummer precipitation anomaly. The fact of increasing (decreasing) trend in the CV frequency (intensity) during 1980 and 2023 may be attributed to the abnormal increase in midsummer rainfall amount over the northeastern TP.