Statistical Characteristics and Synoptic Situations of Long-Duration Heavy Rainfall Events Over North China

The spatiotemporal characteristics of long-duration heavy rainfall (LDHR) events are statistically analyzed using hourly surface observations over central-southern North China during the warm seasons of 2011-2018, revealing pronounced variabilities in the frequency and amount of LDHR. Two accumulated rainfall peaks are found in the western (WHRR) and eastern (EHRR) regions of central-southern North China. The LDHR occurrence frequency decreases westward, and the peaks of the LDHR amount, frequency and intensity in the WHRR and EHRR are observed at nighttime (2100-0200 Beijing Standard Time) or in the early morning (0300-0700 Beijing Standard Time). The rainfall amount exhibits a bimodal diurnal variation in the WHRR (determined mainly by the rainfall intensity), whereas a single rainfall frequency-related peak is found in the EHRR. Four types of LDHR events corresponding to different flow patterns, synoptic systems, and moisture transport mechanisms are classified according to their locations. The first is heavy rainfall in the WHRR with an upper-level jet favorable for an ascending motion near Taihang Mountain; topographic blocking of southerly flow is crucial for heavy rainfall formation. The second describes heavy rainfall in the EHRR attributable to the favorable configurations of upper- and lower-level systems. Heavy rainfall occurs over both the WHRR and the EHRR in the third type, including topographic blocking and convergence associated with low-pressure systems or shear lines and a mesoscale low vortex or shear line related to topographic effects and positive vorticity advection in front of a westerly trough. The fourth shows a scattered distribution of LDHR stations and is generally not comparable to the first three types.