Two types of heavy precipitation in the southeastern Tibetan Plateau

The southeastern Tibetan Plateau (SETP) is the preeminent summer heavy precipitation region within the Tibetan Plateau (TP). Heavy precipitation plays a critical role in regulating regional water resources, glacier mass balance, and ecosystem functions in the SETP. However, the large-scale circulation types and dynamics driving summer heavy precipitation in the SETP remain inadequately elucidated. Using the hierarchical clustering method, two distinctive atmospheric circulation patterns associated with heavy precipitation were identified: the Tibetan Plateau vortex type (TPVT, constituting 56.6% of the events) and the mid-latitude trough type (MLTT, 43.4%). A comprehensive examination of the two atmospheric circulation patterns reveals a clear nexus between the occurrences of summer heavy precipitation and positive vorticity anomalies, moisture convergence, as well as the southeastward displacement of the westerly jet core. Specifically, TPVT is linked to the generation of the TP vortex, which is triggered by the TP sensible heat. The formation of TPVT heavy precipitation is characterized by processes such as potential vorticity development and up-and-over moisture transport on the western TP. These processes drive the development of the TP vortex and its southeastward movement towards the SETP, which finally results in TPVT heavy precipitation. MLTT is associated with the mid-latitude circulation systems. A strong mid-latitude trough and ridge pattern drives the southward flow of cold air from middle and high latitudes to the SETP, converging with warm and humid air transported through the Indian summer monsoon and the westward-extended Western Pacific subtropical high. The interaction between mid-high latitude and subtropical air masses, along with their circulation patterns, leads to the MLTT heavy precipitation. This study advances our understanding of the complex mechanisms governing the summer heavy precipitation in the SETP, shedding light on critical meteorological processes in the region.