Influences of Large-Scale and Mesoscale Circulation Patterns on Precipitation during Rainy Seasons in South China

Abstract Objective circulation classification is a useful method for studying the relationship between atmospheric circulation and weather conditions. However, it may oversimplify synoptic conditions when dealing with a wide range of samples. To address this issue, we apply a two-tier classification scheme combining large-scale and mesoscale circulations to investigate the effect of circulation on rainfall during South China’s rainy seasons. Eight large-scale and seven mesoscale circulation patterns were identified. Each large-scale pattern consisted of two or three primary subsidiary patterns, accounting for over 75% of the total frequency. The study further investigated three typical large-scale patterns, namely, L1, L2, and L3, which are characterized by south-southwest, southwest, and southeast flows over South China, along with their subsidiary patterns. Despite the same large-scale pattern, subsidiary patterns showed differences in both large-scale and mesoscale circulations. As the synoptic flow veered from south to southwest among the subsidiary patterns, the inland rainband gradually moved southeastward to the coastal and offshore regions. Additionally, rainfall propagation modes along the coastlines became more symmetric due to the decreased onshore wind speed. Simulations driven by composite fields of subsidiary patterns produced rainfall distributions that closely matched statistical observations, outperforming those based on L1 and L2 patterns. This finding suggests a stronger link between circulation patterns and rainfall using the two-tier classification scheme compared to the traditional approach. Significance Statement The synoptic classification method has proved to be a valuable method for investigating the links between regional atmospheric dynamics and weather outcomes. However, when dealing with a wide range of synoptic conditions, the classification results can become oversimplified. To address this issue, recent research has proposed a two-tier classification scheme. In our research, we applied a similar two-tier scheme, combined with a quasi-idealized simulation, to investigate the linkages between circulation patterns and rainfall in South China. Our results suggest that the two-tier classification scheme enhances the understanding of rainfall–circulation relationships and improves the accuracy of rainfall prediction.