Synoptic Circulation Forcing of Large-Scale Extreme Precipitation Events Over Southeastern China

Large-scale extreme precipitation (LSExP) events, characterized by widespread extent, persistence, and high intensity, can pose devastating threats to millions of people, infrastructure, and ecology in highly urbanized southeastern China. Here we explore the three-dimensional (spatial and temporal) characteristics and movements of LSExPs and their direct drivers (vertical velocity, water vapor and moisture advection) under six synoptic-scale circulation patterns in southeastern China. LSExPs are classified as low-pressure or non-low types based on circulation anomaly patterns. The low-pressure LSExPs are associated with anomalous cyclonic low-pressure systems in the mid- and lower-troposphere, occurring with main coastal precipitation, while the non-low LSExPs mainly result from cold-warm air convergence and primarily affect inland areas. Low-pressure LSExPs exhibit relatively high intensity compared to non-low types, particularly on days featuring a south-low and north-high dipole pattern, which tend to produce more localized and intense precipitation events. Non-low LSExPs show larger precipitation areas, longer durations, and greater movement distances, and thus impact wider regions, compared to low-pressure LSExPs. Single high-pressure or low-pressure systems are less likely to result in LSExPs, and LSExPs are less severe if occur, compared to other types. All LSExP types move in a direction similar to that of moisture transport, strongly influenced by extreme upward motion of moisture. Low-pressure LSExPs are more related to the upward motion of the atmosphere at 850 hPa, and they also involve extreme water vapor and moisture transport.