The Intensity, Evolution, and Distribution of Cloud-to-Ground Lightning and Radar Reflectivity throughout the Life Cycle of Mesoscale Convective Systems over Southern China

Based on the brightness temperature observed by the Fengyun-4A satellite, eight hundred mesoscale convective systems (MCSs) are identified in the middle reaches of the Yangtze River Basin during the warm seasons of 2018–2021, and these MCSs are categorized into the quasistationary (QS) type and the outward-moving (OM) type. Afterward, the initiations of the MCSs are backward tracked using a hybrid method of areal overlapping and optical flow. Then, the intensity, evolution and distribution of cloud-to-ground (CG) lightning and radar composite reflectivity (CR) associated with MCSs are explored.

The QS-MCSs primarily occur in July and August and are mainly initiated in the afternoon. The OM-MCSs mostly occur in June and July with two initiation peaks at noon and late night, respectively. The QS-MCSs are mainly initiated in mountainous areas. In contrast, the OM-MCSs are mainly initiated in plain areas. Compared to the OM-MCSs, the QS-MCSs show notable diurnal variation in intensity and develop more rapidly. The geographical distribution of CG lightning associated with MCSs shows that the highest occurrence tends to appear over the transition zone of the Poyang Lake Plain and the surrounding mountains. The CG lightning associated with MCSs features a relative lower proportion of negative CG lightning occurrences. An overall negative correlation between brightness temperature and the peak current of CG lightning is documented with seasonal variations. The advection of ice particles associated from convective cores into nearby stratiform regions caused by relatively stronger mid-to-upper-level winds, may explain the positive correlations in May and September. A time lag of 0–2 h between the CG lightning occurrence peak and the MCS extent maximum is found. As the MCS develops, the proportion of convective clouds decreases, the proportion of nonprecipitating anvil increases, and the proportion of stratiform consistently maintains 50%–60% of the MCS extent, dominating throughout its life span. The main region for stratiform is primarily in the southern part of the MCS, while convective clouds are mainly in the northern part, possibly due to the influence of the Meiyu front.