Spatiotemporal characteristics and associated circulation patterns of warm-season precipitation in a complex terrain region of Southwest China

Southwest China frequently witnesses heavy precipitation during warm seasons (May–October) under the joint influence of complex topography and diverse circulation patterns. Based on the objective classification method of spectral clustering, this study identifies three dominant circulation backgrounds and investigates their pivotal roles in determining the warm-season precipitation around Cang Mountain, a complex terrain region in southwest China. Results show that the precipitation characteristics under the three typical circulation patterns are modulated by different dynamic and thermodynamic processes, and each of which has its own seasonality and diurnal variations. Cluster 1 reveals that the northeasterly winds generated by the low-level shear line and vortex on the east side of the Tibetan Plateau provide favorable dynamic conditions for the southwestward evolution of precipitation. As the zonal (meridional) components of northeasterly winds are intensified in the nighttime (daytime), the diurnal cycle of precipitation is manifested with a major (secondary) peak in the early morning (late afternoon). Cluster 2 is featured by the northward advance of the Western Pacific Subtropical High (WPSH) and the monsoon trough over the tropical region. Moreover, there is a high frequency of intense precipitation influenced by the relatively strong thermal instability. With the low-level southeasterly winds strengthening upstream of Cang Mountain at night, the diurnal cycle of precipitation exhibits a pronounced early-morning peak. In Cluster 3, southwesterly winds prevail around Cang Mountain under the configuration of the Indian-Myanmar trough and the strengthened WPSH. The precipitation shows a high percentage of weak intensity due to the relatively weak unstable stratification. These findings offer valuable insights into how circulation patterns impact the fine-scale precipitation processes over complex terrains.