Fine-scale characteristics and dominant synoptic factors of spring precipitation over complex terrain of the southeastern Tibetan Plateau

Abstract

Spring precipitation over the southeastern Tibetan Plateau (SETP) produces more than 34% of annual precipitation, which is comparable to summer precipitation. This pre-monsoon rainfall phenomenon, influenced synthetically by atmospheric circulations and topography, makes the SETP an exception to its surroundings. Here, fine-scale characteristics and typical synoptic backgrounds of this unique phenomenon have been investigated. The spring precipitation over the SETP is characterized by high frequency at hourly scale, with a single diurnal peak at night. Event-based analysis further demonstrates that the spring precipitation is dominated by long-lasting nocturnal rainfall events. From early to late spring, the dominant synoptic factor evolves from terrain-perpendicular low-level winds to atmospheric moisture, influencing the spatial heterogeneity and fine characteristics of the spring precipitation. The westerly-dominated type, featured by lower geopotential height over the TP and enhanced westerlies along the Himalayas, produces limited-area precipitation at those stations located at topography perpendicular to low-level winds. In contrast, the moisture-dominated type is featured by an anomalous cyclone over the Bay of Bengal and induces widespread precipitation around the SETP, which is the leading contributor to the spring precipitation there. Due to the moist environment and weak instability, the spring precipitation influenced by the moisture-dominated type is characterized by long-lasting nocturnal events, with a large portion of weak precipitation. Findings revealed in this study complete the picture of spring precipitation influenced by different dominant synoptic factors over the SETP, which deepen the current understanding of the joint influence of circulation and topography on the hydrological cycle of complex terrains.