Initiations of Mesoscale Convective Systems in the Middle Reaches of the Yangtze River Basin Based on FY‐4A Satellite Data: Statistical Characteristics and Environmental Conditions

Abstract

AbstractBased 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 (April–September) of 2018–2021, and these MCSs are categorized into the quasistationary (QS) type and the outward‐moving (OM; i.e., moving beyond the source region) type. Afterward, the initiations of the MCSs are backward tracked using a hybrid method of areal overlapping and optical flow. Then, the main features of QS‐MCSs and OM‐MCSs and their respective synoptic circulations and environmental parameters are analyzed. 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. Circulations of a total of 285 days (without direct influences from tropical cyclones) are objectively classified into three patterns by using the k‐means algorithm. Pattern‐I, which is closely related to low‐level jets, shows the most similar features to those of typical Mei‐yu fronts, and it acts as the most favorable circulation type for MCS initiations. Pattern‐II is dominated by northwesterlies, with a relatively stable layer in the low‐level troposphere. Pattern‐III features a dry‐adiabatic or even a superadiabatic layer that contributes to decreasing the layer stability.