Abstract
<title>Abstract</title> <p>Using data from automatic weather stations, Doppler radar, and ERA5 reanalysis, this study examined the differences in triggering and maintenance mechanisms, as well as the origins of extreme gales, between two squall lines that impacted the region spanning southern North China to the Huanghuai area on June 13, 2022. This event unfolded against the backdrop of a Northeast China Cold Vortex. Presence of strongly unstable stratification, marked by cold and dry mid-level air juxtaposed with warm and moist low-level air, created conducive conditions for convective outbreaks. The triggering mechanisms of the two squall lines diverged. Squall Line I was clearly triggered by a combination of factors: a synoptic-scale shear line, a mesoscale surface vortex, and its associated convergence line. Subsequently, it was organized through convective merger processes. In contrast, Squall Line II emerged without significant synoptic-scale forcing. Its initial convection was triggered by the thermal effects of the Taihang Mountains’ topography and was later organized by the convergence line formed through the interaction between low-level easterly winds and the terrain, coupled with frontogenetic dynamic forcing. Significant differences were also observed in their maintenance mechanisms. Squall Line I exhibited a long lifespan and wide impact range, maintained by a sustained equilibrium between the propagation speed of the cold pool and low-level vertical wind shear. In contrast, Squall Line II had a short lifespan and small scale, primarily due to a rapid disruption of the balance between these two factors. Furthermore, the physical mechanisms underlying the extreme gales varied. For Squall Line I, the gales were predominantly driven by outflow generated by the strong pressure gradient associated with a large-scale, high-intensity cold pool. For Squall Line II, localized extreme gusts were more closely linked to the small- to medium-scale bow echo structure, the strong rear-inflow jet that developed within it, and the dynamic processes associated with the mesoscale vortex.</p>