Abstract Boundary layer jets (BLJs) over the South China Sea (SCS) are key regulators of heavy rainfall in South China, yet their structural diversity and associated rainfall impacts are not well quantified. Using ERA5 reanalysis, we apply a Self‐Organizing Map algorithm to objectively classify BLJ structures during the early summer rainy season. Six distinct BLJ types are identified, categorized by their jet‐core location (southern or northern SCS) and prevailing wind direction (southerly, southwesterly, westerly, and easterly). These types exhibit distinct seasonal and diurnal variability, with their type transitions closely linked to the evolution of synoptic‐scale systems over South China. Three of the identified types constitute a “rainy BLJ group” responsible for most heavy rainfall. These BLJ types generate dynamic forcings (e.g., coastal convergence, terrain blocking, double‐jet configurations) and modulate thermodynamic conditions (e.g., spatial variations in CAPE and CIN), leading to strongly BLJ‐type‐dependent rainfall responses. Notably, the relationship between BLJ intensity and rainfall is non‐monotonic and highly sensitive to jet structure: north‐core southwesterly jets enhance coastal rainfall, whereas south‐core and north‐core southerly jets may suppress it by transporting more stable air. This study establishes a type‐dependent framework that advances understanding of BLJ diversity over SCS and provides new insights into how jet structure controls rainfall variability in South China.
Guo et al. (Tue,) studied this question.