ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Numerical Simulation Study of Severe Convection Triggered by the Collision Between a Gust Front and a Sea-Breeze Front in Xiamen
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Abstract:
Using conventional observations, dense surface automatic station data, NCEP/FNL reanalysis, Doppler radar data, and WRF model simulations, this study investigates a severe convective event triggered by the collision between a gust front and a sea breeze front in Xiamen, China, and examines its underlying mechanisms. The results show that the 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 to form 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 convection. WRF simulations further indicate that following the collision, the shallow-layer specific humidity in the collision region 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?? s?1, suggesting significant enhancement of moisture supply, instability, and dynamic lifting. The convergence-induced ascent 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 and produced short-duration heavy rainfall in Xiamen. Thereafter, a surface convergence line and shallow shear system on the rear side of the collision region maintained a deeper convergence-ascent structure. In combination with sufficient moisture and instability, the model indicated a subsequent convective regeneration process. The findings suggest that the collision between a gust front and a sea breeze front can trigger and sustain severe convection through enhanced low-level convergence, moisture transport, and instability, providing useful implications for nowcasting and warning of local severe convection in Xiamen and other coastal areas.
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