Spatiotemporal Characteristics and Associated Synoptic Patterns of Extremely Persistent Heavy Rainfall in Southern China

Abstract

AbstractPersistent heavy rainfall has a longer duration than short‐duration heavy rainfall (SHR), with few studies on its extreme duration. Hourly gridded precipitation data from April to September during 2008–2019 were used to define and study extremely persistent heavy rainfall (EPHR) in southern China. It was found that the EPHR process was asymmetric, with growing time about 1 h shorter than fading time on average. On average, EPHR accounts for less than 40% of duration but nearly 3/4 of precipitation in events. There was a tendency for EPHR to occur near land‐sea boundaries and mountainous areas. It was more frequent in the early morning, differing from the “afternoon peak” observed for SHR. There were five EPHR high‐incidence areas (HIAs). EPHR with longest duration occurred in coastal areas, and the largest precipitation was recorded near the Yunkai Mountains. Influenced by local characteristics, the peaking time of monthly and diurnal variations differed in HIAs. The low in Beibu Gulf was closely related to the occurrence of EPHR, but the relative positions of the low and HIAs varied in different synoptic pattern types. The trough at 500 hPa and the low vortex or shear line at 850 hPa interacted with the surface convergence mechanism to produce strong upward motion. There was also a warm and wet tongue at 850 hPa above the HIAs, combined with the vertically integrated moisture flux convergence. Additionally, the marine boundary‐layer jet and isentropic ascent in lower troposphere possibly supported the coastal EPHR.