Spatiotemporal Distribution and Variation Characteristics of Convective Activities in Different Climate Zones in Northern China Based on 25 Years of Satellite Observations

Northern China's complex climatic transitions between arid, monsoon and transitional zones create spatially divergent convective regimes with cascading impacts on extreme weather. Using 25 years (1996–2020) of multi-satellite observations, this study reveals that convective activities (CA) and deep convective activities (DCA) exhibit pronounced spatiotemporal heterogeneity governed by topography-circulation interactions. The eastern Tibetan Plateau slopes and Northeast China plains emerge as persistent hotspots, sustaining warm-season CA frequencies > 4.5% with amplified diurnal cycles (peak-trough differences > 3.4%), driven by plateau-induced thermal updrafts and nocturnal low-level jet convergence. In stark contrast, northwestern deserts show minimal activity (< 0.4%) but extreme interannual variability (coefficient of variation > 1.0), reflecting unstable moisture supply from fluctuating westerly troughs. Seasonally, May dominates convective intensity (8% CA frequency) as mid-latitude baroclinic systems collide with radiative heating, while September's minimum (0.6%) coincides with Western Pacific Subtropical High retreat. Unique to transitional zones, the Tibetan slopes host a secondary July DCA maximum (> 3%) fueled by South Asian High-enhanced moisture transport. Mechanistically, random forest (RF) attribution identifies the Western Pacific Subtropical High (26% influence) and Tibetan Plateau thermal forcing (22%) as primary regulators—the former modulating monsoonal moisture influx, the latter amplifying convective instability through plateau-scale ascending motions. Transitional zones further respond to Eurasian zonal circulation shifts, explaining their hybrid diurnal signatures blending monsoonal and arid-region characteristics. By bridging satellite climatology with dynamical diagnostics, this work establishes a hierarchical framework where regional topography orchestrates continental-scale circulation feedbacks. The identified thresholds (e.g., 3.4% diurnal amplitude, 1.0 the coefficient of variation interannual variability) provide actionable metrics for forecasting convective extremes across climate transition zones—a critical advance for disaster resilience in vulnerable northern China.