Mountain-to-plain mesoscale convective systems in North China: propagation patterns and precipitation characteristics under varied synoptic-scale environments

Mesoscale convective systems (MCSs) frequently propagate from China’s second-step terrain to North China Plain (NCP), yet the regime dependence of their spatiotemporal characteristics and the controlling environments remains insufficiently understood. Using Himawari-8/9 brightness temperature data and an iterative tracking approach, this study identified warm-season mountain-to-plain MCSs (MP-MCSs) over North China during 2016–2023. K-means clustering separates these MP-MCSs into four major categories: short-distance northeastward/southeastward moving (Short-NE/Short-SE) and long-distance northeastward/southeastward moving (Long-NE/Long-SE) MP-MCSs. Short-distance MP-MCSs initiate mainly over the Taihang–Yanshan region and occur most frequently during the monsoon season, producing rainfall maxima along the slopes and adjacent plains. Long-distance MP-MCSs originate farther upstream and are more common during seasonal transition periods, with rainfall concentrated over western mountainous regions. All four categories exhibit enhanced frequencies of intense hourly precipitation over the plains. Short-SE systems are the most convectively intense but spatially compact and slow moving, whereas Long-NE systems are the least intense, have the broadest cloud shields, and move the fastest. The diurnal rainfall evolution also differs systematically by propagation direction and significantly terrain-dependent. NE-moving systems peak from late-afternoon to evening over the eastern Taihang slopes and adjacent foothills, whereas SE-moving systems, especially Short-SE, display a pronounced mountain-to-plain phase delay, with afternoon rainfall over high terrain and nocturnal rainfall over foothills and plains. Composite environments indicate that the four regimes are favored by baroclinic waves, local thermodynamic and topographic forcing, midlatitude troughs, and cold-vortex-related northwesterly flow, respectively. These results refine the regime-based understanding of MP-MCS propagation and heavy-rainfall risk over North China.