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

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

Peiyu Wang and Zhiyong Meng

Laboratory for Climate and Ocean–Atmosphere Studies, Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing, China

ABSTRACT

Mesoscale convective systems (MCSs) often cause disastrous weather conditions, such as heavy rainfall, hail, thunderstorms, and tornadoes. Severe weather associated with MCSs is closely related to their organizational modes. Previous study proposed a new organization of MCSs that contains multiple parallel rain bands (MPRBs), which tends to produce extremely heavy rainfall. There are two types of train effects in an MCS containing MPRBs. One is that the convective cells move along individual rain bands which is referred to as echo training, and the other is that the parallel rain bands move along the direction of movement of MCS, which is denoted as band training. Therefore, the presence of MPRBs is often accompanied by heavy precipitation. This study is aimed to document the general features of MCSs with MPRBs in China from 2016 to 2020, including temporal and spatial distributions, morphologies, their associated precipitation patterns and environmental features.

A total of 177 cases of MCSs with MPRB features were identified based on the basic radar reflectivity at a 0.5° elevation angle from 2016 to 2020 in China. MPRBs were classified into the initiation type (~40%), which rain bands initiate and develop individually, and differentiation type (~60%), which rain bands form through the splitting or merging. The results showed that the formation time of these MCSs peaked in July with a bimodal diurnal variation including a major peak at midnight and a minor peak in the morning. The highest occurrence frequency of these MPRBs was observed in the northern Beibu Gulf and its coastal areas, with some minor high frequencies in Guangdong, Jiangxi, and southern Shandong provinces. MPRBs mainly contained 3-4 rain bands with an orientation generally consistent with the direction of 0-1 km wind shear. The movement of MPRBs generally proceeded slower than that of squall lines in East China, with the movement speed of MPRBs mainly ranging from 4 to 8 m s^-1, and rain bands mainly ranging from 8 to 12 m s^-1. There were 76.8% of cases accompanied by train effects and 62.7% existed in areas that overlap with cold pools. Likely resulting from the slower movement and train effects, 71% of these MPRBs was associated with an enhanced hourly maximum precipitation. The severity of rainfall accumulation may be alleviated to a certain extent by the generally short duration of MPRBs, with two-thirds of the total cases exhibiting a duration shorter than 1.5 h.