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Abstract:
Convective initiations (CIs) in western Jiangnan, China, were examined using radar data spanning April–September 2018–2021. Our approach combined objective identification and subjective validation to identify, track, and validate the CIs, thereby producing a highly accurate CI dataset. Using this dataset, we investigated the spatiotemporal variations and environmental conditions associated with CIs and revealed distinct seasonal and diurnal patterns of CI events. Spatially, CIs occur more frequently south of the Nanling Mountains and less frequently in the north. Seasonally, they were most frequent from June to August, and least frequent in April and September, following a unimodal distribution. The CIs exhibited pronounced afternoon convection, particularly from June to August, when most occurred between 11:00 and 19:00 local time (UTC+8 h). Terrain significantly influenced the spatial variation in the CIs. North of the Nanling Mountains, CIs occurred near higher mountains, whereas south of the range, they were concentrated near smaller mountains and along the Guangdong coast. Using K-means clustering, CIs that could develop into Mesoscale Convective Systems were classified into four circulation types: Western Pacific subtropical high (WPSH) control (Type Ⅰ), WPSH edge (Type Ⅱ), southwest airflow (Type Ⅲ), and low trough shear (Type Ⅳ). The CIs of Types I and II were primarily attributed to afternoon thermal convection, which occurs under conditions of high moisture and thermal instability. Triggers for these CIs mostly occurred near high-elevation terrain. In contrast, Types III and IV were driven primarily by the synergy of abundant moisture conditions and synoptic dynamic factors, such as low-level jets, upper-level troughs, and shear lines. These types exhibited higher frequency in the south, with high-frequency CI trigger zones particularly observed in regions with strong moisture-flux convergence and near complex terrain.
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