Anomalies of Precipitation over China on Days with Tropical Cyclone Activity over the Bay of Bengal: Role of Moisture Transport

Tropical cyclones over the Bay of Bengal (BoBTC) affect the precipitation over China, with distinct seasonal and daily variabilities. This study quantitatively examines the daily standardized precipitation anomalies (SPAs) over China on the days with BoBTC activities (storm-days) and related circulations, based on rainfall measurements at surface meteorological stations and ECMWF reanalysis data on a 0.25° × 0.25° resolution during 1979–2019. Significant positive SPA is found over the stations in the two adjacent regions around BoB (Southwest China in May/November and southern Tibetan Plateau in October) and three distant regions (Southeast China and the northeastern boundary of the Qinghai–Tibet Plateau in May, and central North China in October). The SPA distributions are remarkably consistent with the integrated water vapor transport (IVT) anomalies. Enhanced IVT is found associated with the interaction between southwesterly (southerly) of the BoBTC circulation and low-level monsoonal flow in May (midlevel westerly in winter months). The probabilities of extreme precipitation (EP) occurrences over the above regions all increase on storm-days. For adjacent regions, EP is significantly correlated with the northward IVT anomalies to the east of BoBTC circulation, which strengthen the water vapor input through the southern border. Such IVT anomalies are stronger in May, benefited by the deep monsoonal southwesterlies than those in November. For distant regions, EP is more closely related to the IVT anomaly extending back from BoB. Enhanced moisture from BoB concentrates along a local low-level convergence line over Southeast China, being further facilitated by coexistence of the BoBTC depression and midlevel westerly trough in midlatitudes. Our results highlight the interactions between BoBTCs and local weather systems that influence the general precipitation anomalies and occurrence of EP over China, especially over distant regions.