Morphological Characteristics of Mesoscale Convective Systems Formed in the Middle Reaches of the Yangtze River Basin and Their Evolution Patterns

Based on the extent and eccentricity characteristics, mesoscale convective systems (MCSs) formed in the middle reaches of the Yangtze River Basin were classified into six subtypes: large circular (LC), large elongated (LE), medium circular (MC), medium elongated (ME), small circular (SC), and small elongated (SE). The lifespans of all L-scale and most M-scale MCSs exceed 6 h, whereas the majority of S-scale MCSs last less than 6 h. The cold cloud coverage frequency for E-type MCSs exhibits relative uniformity, with high-frequency regions located south of the Yangtze River. In contrast, C-type MCSs display a more scattered high-frequency distribution with higher maxima. E-type MCSs predominantly retain an elongated shape throughout their life cycles. Additionally, as the area of LE and ME MCSs expands, their eccentricity progressively decreases, leading to a greater inclination towards the east–west direction. For C-type MCSs, they maintain a circular shape for less than half of their duration but tend to adopt an elongated shape during the development or dissipation stages. These findings provide a foundation for further investigation into the formation mechanisms and associated mesoscale systems of MCSs, which could enhance the prediction accuracy of the location and intensity of severe weather events linked to different types of MCSs.