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-seasonal nocturnal rainfall—remain unknown due to scarce high-resolution vertical wind observations. Here, we reveal the multiscale responses of LLJs within 2 hours 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 hours leading up to their onset. In monsoon regions, ~40 % of nocturnal HR (LLJ_HR) were LLJ-associated and had higher heavy rainfall probability than non-LLJ_HR. Critically, these LLJ_HR events depended on rapid, coupled minute-scale dynamical intensification, typically occurring 30 to 120 minutes before rainfall initiation. Specifically, coherent changes in LLJ wind profiles, frequency, vertical wind shear, and pronounced evolution in jet height were observed, operating in synergy with substantial thermodynamic instability. This behavior stood in sharp contrast to LLJ_non-HR events, which were characterized by relatively stable, weakening, or declining LLJ evolution and an inadequate thermodynamic response. These findings demonstrate that a minute-scale 'rapid reorganization' of dynamic and thermodynamic conditions driven by swift evolution of the LLJ is essential for nocturnal HR, providing observational constraints for regional model parameterizations and nowcasting.