General Features of MCSs with the Organization of Multiple Parallel Rain Bands in China

Abstract

Multiple parallel rain bands (MPRBs) involve the organization of mesoscale convective systems characterized by multiple parallel convective rain bands, which may produce high rainfall accumulation. A total of 178 MPRBs were identified from 2016–2020 in China, which were classified into the initiation type (~40%), where rain bands initiate individually, and differentiation type (~60%) where rain bands form through the splitting of larger rain band or merging of smaller cells. Results showed that the occurrence frequency of MPRBs peaks in July with a midnight major peak and a morning minor peak. The highest occurrence frequency is observed in the northern Beibu Gulf and its coastal areas, with minor high frequencies in Guangdong, northern Jiangxi, and southern Shandong provinces, typically in a southwesterly low-level jet to the west of the subtropical high. MPRBs mainly contain 3–4 rain bands with a spacing distance of 30–50 km and an orientation generally consistent with the direction of 850 hPa winds and 0–1 km vertical wind shear. MPRBs generally move slower than that of squall lines in East China ranging from 4 to 8 m s−1 with 16% being quasi-stationary, which is mainly due to the occurrence of band back building mainly associated with cold pool. Most MPRBs have training effects with band training as the dominant mode. Because of the band training effect and slower movement of MPRBs mainly due to band back building, 71% of MPRBs are associated with enhanced maximum hourly precipitation. Rainfall severity may be alleviated somewhat by the generally short duration of MPRBs with 78% being shorter than 2 h.