Revealing Key Dynamical Mechanisms of a Severe Supercell within a QLCS Using Rapid Update 4DVar Assimilation of C‐band Phased Array Weather Radar Data

Supercells represent the most intense and vigorous type of convective storms, often associated with severe weather phenomena such as large hail, damaging winds, and tornadoes. This study investigates a supercell embedded within a quasi‑linear convective system (QLCS) that occurred over Beijing on 12 June 2022. This storm produced large hail with diameters of 3–5 cm in Miyun and Shunyi Districts, resulting in significant economic losses. By assimilating high spatiotemporal‑resolution observations from a C‑band phased array radar (PAR) into a four‑dimensional variational data assimilation system, we examine the dynamical processes responsible for the supercell’s development and its associated mesocyclone.   

Our findings reveal that prior to convective initiation, a pronounced convergence zone formed west of the terrain, generating several meso‑γ‑scale vortices near the surface. During the vertical merger of the convective cell with the QLCS, a strong QLCS-driven downdraft enhanced low‑level horizontal convergence, stretching the embedded vortices and markedly increasing vertical vorticity. In the mature stage, a mesocyclone developed with its rotational center reaching 4.5 km altitude and a maximum rotational velocity of 20 m s⁻¹.

The analysis demonstrates that the surface convergence lines and the meso‑γ‑vortices along them strengthen low‑level convergence and generate strong updrafts, triggering the initial storm. These intense updrafts effectively convert horizontal vorticity into vertical vorticity and transport it upward. Furthermore, the process of convective merging reinforces low‑level horizontal convergence, which forcibly stretches the mesovortex, enhancing vertical vorticity. These mechanisms enable the convective storm to develop in a strong, organized manner, ultimately leading to the formation of the supercell storm.

 Overall, this study highlights the critical role of terrain‑induced convergence, meso‑γ‑scale vortices, and convective merging in the initiation and intensification of supercell storms within QLCS environments. The high‑resolution PAR observations and assimilation techniques employed here provide valuable insights into the multiscale interactions that govern severe convective weather, with important implications for operational forecasting and early warning systems.