Characteristics of Mei-Yu Season Mesoscale Convective Systems over Central-Eastern China

Meiyu rainband is characterized by successive development of the organized mesoscale convective systems (MCSs) along the frontal zone. These MCSs contribute more than half of the Meiyu total precipitation regionally and are responsible for many of the major flooding events along the Yangtze River basin. This study focuses on investigating the cloud and precipitation features of MCSs in central and eastern China using satellite observations and reanalysis data during the 2016-2018 Meiyu periods. The MCSs’ properties are found to have relatively large variability in terms of the occurrence number, rainfall amount and rainfall intensity during the study period, with the most occurrence frequency of MCS and the most intense precipitation in 2016, following by 2018 and 2017. The convective initiation time, duration and diurnal cycle of precipitation produced by MCSs have less discrepancies during the study period, as these characteristics are largely driven by the synoptic conditions. A peak of MCSs’ rainfall amount occurs in the early morning, which is associated with the MCSs’ genesis enhanced by the nocturnal low-level jet (LLJ) overnight and the large stratiform region to be generated before the sunrise. Although 2018 has the shortest Meiyu period, the contribution of MCSs’ precipitation to the total Meiyu’s precipitation is the highest, indicating that the MCS activity is the most active in 2018. By examining the low- and upper-level environmental variables, it is found the MCSs in 2018 are characterized by the highest moist availability and LLJ strength with strong updraft penetrating to mid-level, producing favorable thermodynamic condition for convective development.