A Diagnostic Case Study on the Comparison Between the Frontal and Non-Frontal Convective Systems

Two major mesoscale convective clusters of different characters occurred during the heavy rainfall event in Guangxi Region and Guangdong Province on 20 June 2005,and they are preliminarily identified as a frontal mesoscale convective system (MCS1;a frontal cloud cluster) and a non-frontal MCS (MCS2;a warm sector cloud cluster).Comparative analyses on their convective intensity,maintenance mechanism,and moist potential vorticity (MPV) structure were further performed.The convective intensity analysis suggests that the ascending motion in both the frontal MCS1 and the warm sector MCS2 was strong,so it is hard to conclude whether the intensity of the frontal convective cluster was stronger than that of the nonfrontal convective cluster,and their difference in precipitation might result from differences in their moisture conditions.The comparative analysis of the maintenance mechanisms of matured MCS1 and MCS2 show that in MCS1 there were strong northerly inflows at middle and upper levels,and the convection was mainly maintained through convective-symmetric instability;while in MCS2,the water vapor was abundant,and the convection was maintained by moist convective instability.The structural analysis of MPV indicates that (1) the two dusters were both potentially symmetric unstable at middle and low levels;(2) there were interactions between the cold/dry air and the warm/wet air in the frontal MCS1,and the interactions between the upper- and low-level jets in the warm sector MCS2;(3) the high- and low-level jets and moisture condition nearby the convective clusters exerted different impacts on the two types of convective systems,respectively.