Exploring the spatiotemporal variations and key environmental conditions of convective initiations in the Western Jiangnan Region of China

This study investigated convective initiations (CIs) in the western Jiangnan region of China using radar data spanning April to September from 2018 to 2021. An integrated approach combining objective identification and subjective validation was applied to identify, track and validate CIs, resulting in a more accurate CIs dataset. Based on this dataset, this study delved into the spatiotemporal variations and key environmental conditions associated with CIs. The results indicated distinct seasonal and diurnal patterns in CIs events. Seasonally, the spatial variations of CIs were demarcated by the Nanling Mountains, exhibiting higher frequency to the south and lower to the north. Generally, the seasonal distribution of CIs followed a unimodal pattern, peaking during June to August and reaching minima in April and September. Notably, CIs exhibited a pronounced convection feature in the afternoon, particularly during June to August, when the majority of CIs occurred between 11:00 and 19:00. Furthermore, the spatial variations influenced by terrain were prominent. With the Nanling Mountains as the dividing line, CIs in the northern region were located near relatively higher mountains, while in the southern region, they were concentrated in smaller mountains and coastal areas. Utilizing the K-means clustering method, CIs that could develop into Mesoscale Convective Systems are classified into four circulation types: the Western Pacific Subtropical High (WPSH) Control type (Type I), the WPSH Edge type (Type II), the Southwest Airflow type (Type III), and the Low Trough Shear type (Type IV). CIs under Type I and II were primarily attributed to afternoon thermal convection occurring under conditions of strong moisture and thermal instability. The distribution of CIs triggers for these types tended to cluster in the vicinity of high-elevation terrain. In contrast, CIs belonging to Type III and IV were primarily driven by the synergy of abundant moisture conditions and systematic dynamic factors such as low-level jets, upper-level troughs, and shear lines. These exhibited a north-low and south-high frequency distribution, with high-frequency CIs trigger zones observed particularly in regions of strong moisture flux convergence and near complex terrain.