A Dual Regime of Mesoscale Convective Systems in the East Asian Monsoon Annual Cycle

Eastern China is perennially hit by mesoscale convective systems (MCSs), yet it remains an open question as to whether and how their general properties change throughout the annual cycle. By leveraging high-resolution satellite observations a hybrid tracking algorithm, we present 20-year (2001–2020) climatology of MCSs over eastern during eight subseasonal-to-seasonal (S2S) monsoon stages. contribute up 50% stage-total precipitation 60% rainband-zone Pre-Meiyu Meiyu episodes, contributions remain non-trivial transition seasons. We discover two contrasting regimes that alternate immediately upon Fall onsets. The wintertime regime features fast-propagating shallow initiated at night in strongly sheared dry environment. summertime regime, instead, outbreak south, where often initiate afternoon propagate 2–3 times slower than cold-season ones. Based on multivariate clustering analysis, nighttime dictate winter stages deep nocturnal boundary layer with moist rear inflows upgliding above it. In contrast, afternoon-initiated under feature pronounced available potential energy (CAPE) "tongue" upslope flows southeast quadrant. southwesterly ascending are likely inhibition tip CAPE tongue facilitate intense updrafts MCSs. Findings here may offer insights into S2S weather prediction agricultural water management year.