Abstract:Using conventional observations, surface automatic meteorological station data, NCEP/FNL reanalysis, Doppler radar data, and WRF model simulations, this paper studies a severe convective event triggered by the collision between a gust front and a sea-breeze front in the Xiamen Region, and also analyzes its underlying mechanisms. The results show that this event occurred at the edge of the subtropical high, where upper-level divergence overlapped with low-level convergence. An unstable thermodynamic stratification characterized by dry upper levels and moist lower levels, together with strong thermal instability, provided a favorable environment for convective development. The cold outflow generated by earlier convective cells expanded outward forming a gust front, while the sea-breeze front developed continuously along the Xiamen coast. After the two boundaries collided near the urban area of Xiamen, low-level convergence and local lifting were markedly enhanced, thereby initiating the severe convection. WRF simulations further indicate that following the collision, the shallow-layer specific humidity in the collision zone increased by about 2.5 g·kg-1, the maximum convective available potential energy increased by more than 1000 J·kg-1, and the vorticity intensified to 25×10-4 s-1, which indicate significant enhancement of moisture supply, instability, and dynamic lifting. The convergence-induced ascending motion allowed air parcels to overcome the level of free convection, thereby initiating and sustaining convection. Subsequently, convective cells near the collision zone merged and triggered a cloud-bridge cell, which further developed into a multicellular merging process. Thereafter, a surface convergence line and shallow shear system on the rear side of the collision area maintained a deeper convergence-ascending structure, and with sufficient moisture and instability, a subsequent convective regeneration process occurred. The findings could provide a useful implication for nowcasting and warning of local severe convection in Xiamen and other coastal regions.