Abstract. Nocturnal rainfall initiation is closely linked to low-level jets (LLJs), but national-scale LLJ features over China – especially their evolution preceding warm-season nocturnal rainfall – remain unknown due to scarce high-resolution vertical observations. Here, we reveal the fine vertical structure of LLJs and their rapid evolution within 2 h preceding the onset of nocturnal heavy rain (HR) and non-HR across four phases of rainy seasons in China during the warm season (April–October) of 2023–2024, utilizing data from a nationwide network of radar wind profilers (RWPs) in combination with surface observations and reanalysis data. Results show that nocturnal rainfall accounted for over 50 % of warm-season rainfall, with 56 % preceded by LLJs within 2 h of its onset. In monsoon regions, ∼45 % of nocturnal HR were LLJ-associated (LLJHR), producing heavier rainfall than non-LLJHR events. Critically, LLJHR events underwent a minute-scale “rapid reorganization” of the LLJ structure, characterized by oscillatory evolution in jet height, frequency and strength. This creates a favorable environment for the “final-stage intensification” of dynamic field during the last ∼30 min, where widespread intensification of jet – coupled with significant thermodynamic instability – acts as a primary dynamical forcing mechanism and a key precursor signal for HR initiation. In stark contrast, LLJₙon-HR events exhibited quasi-steady or weakening dynamical trends, accompanied by an inadequate thermodynamic response that lacks such synergistic coupling. These findings demonstrate that minute-scale dynamic adjustments driven by swift evolution of the LLJ are essential for nocturnal HR, offering critical observational constraints for regional model parameterizations and nowcasting accuracy.
Li et al. (Wed,) studied this question.
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