On the nationwide variability of low-level jets prior to warm-season nocturnal rainfall in China revealed by radar wind profilers

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 (LLJ_HR), producing heavier rainfall than non-LLJ_HR events. Critically, LLJ_HR 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, LLJ_non-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.