Tracking Warm-Season Mesoscale Convective Systems over the Tibetan Plateau and Their Impact on Sichuan Heavy Rainfall

Mesoscale convective systems (MCSs) over the Tibetan Plateau (TP) play a critical role in downstream heavy rainfall over Sichuan. However, conventional single-threshold identification and area-overlap tracking methods often suffer from substantial misidentification in plateau regions, primarily due to cold cirrus contamination and incomplete life-cycle representation. In this study, an improved area-overlap combined with Kalman-filtering (AOL-KF) tracking algorithm is developed for warm seasons (May–October) during 2019–2023 over the TP by introducing a rainfall constraint. FY-4A blackbody brightness temperature is jointly used with GMCP merged precipitation through a rain-rate threshold, with FY-4A cloud type serving as auxiliary information. The rainfall constraint is further evaluated using Ka-band ground-based millimeter-wave cloud radar observations at Naqu and Yushu during July–August 2020. Results show that cirrus-induced false identification is effectively suppressed, and the identified MCSs are more consistent with radar observations. Trajectory reconstruction indicates that potential MCSs are mainly distributed east of 85°E and south of 35°N, with 61.14% propagating eastward. Only 1.85% of TP MCSs move off the plateau, and 0.93% further affect Sichuan. MCS translation speed exhibits a clear meridional gradient and is significantly modulated by mid–upper-level (200–400 hPa) flow. A representative case demonstrates that TP-origin MCSs intensify over Sichuan due to enhanced moisture convergence, secondary circulation, and atmospheric instability.