Life Cycle Characteristics of MCSs Tracked by Geostationary Satellite

Mesoscale convective sytems (MCSs), the largest of the convective storms, contribute a large proportion of heavy precipitation annually in tropics and mid-latitudes. The region between Yangtze River and Huaihe River in East China is frequently influenced by MCSs especially in warm season. This study used infrared images from MTSAT-1R geostationary satellite together with CMORPH precipitation estimates data to automatically identify and track MCSs in the region mentioned above between May and August, 2008 and 2009. The MCSs were classified into 3 categories – convective center, system and complex – by different brightness temperature thresholds. MCS formation time was first determined by both radiative and precipitation parameters, then start from MCS formation time, the system was tracked backward till the genesis of the cloud, and forward till the disappearance or outside the region of interest. The samples MCSs tracked were further confined by geological range and life duration. By this method, 280 MCS events of deep convection and strong precipitation were selected as samples for analyzing their features. 75% of convection events last over 5h, and spent over 1/5 of their life time from formation to the moment starting to decay. The maximum cloud area exceeds 10⁵ km² mostly, and precipitation covers the area about 10⁴ km². MCSs in this region form most frequently in the late afternoon and at dusk, similar pattern to MCSs in tropics. While the second most frequent period for MCS formation is early morning, which may be triggered by low jet streams. Based on our results, systems with relatively lighter precipitation (maximum precipitation rate throughout life time less than 15 mm/h) or longer life duration (over 24 h) or smaller cloud size (the maximum system area less than 50,000 km²) have higher possibility to form during this period. This research studied 4 variables as mature indexes to show the sign of MCS developing to its maturity – the minimum of brightness temperature, the maximum of precipitation rate, the maximum of convective system area, and the maximum of related precipitation area. The statistic result suggests that the MCSs tend to first reach the maximum of precipitation rate, then the minimum of brightness temperature, then the maximum of related precipitation area, and at last the maximum of system area. Places for the most frequent MCS formation occur at the border of 4 provinces – Shandong, Henan, Anhui and Jiangsu. The spots of highest cloud-tops and of the strongest precipitation rates do not match perfectly. For the time when MCSs start to dissipate, cloud-tops reach places over the sea, while the largest precipitation rates still stay on land. Based on the results of regression, MCSs with longer life duration tend to have higher cloud-tops, heavier precipitation, spend longer time in development, and their anvils and precipitations cover larger area. During life time, the times of mergers significantly overpass that of splits. According to the regressions between times of mergers or splits and MCS life duration, the increase of times of mergers extends life time, however, with longer life duration, the times of splits does not increase significantly. The results demonstrate the theory that splits tend to weaken convection while mergers strengthen convection.