Abstract:
From 1300 to 1600 BJT on May 30, 2024, downslope-enhanced convective storms in the Beijing urban area triggered destructive winds that reached 12 on the Beaufort scale, causing severe damage, including the toppling of utility poles and large trees with a diameter at breast height exceeding 1 m. This study combines damage surveys with polarimetric Doppler weather radar observations to investigate the characteristics of the disaster and the physical processes associated with the severe winds. The results show that the destructive winds exhibited westward divergent patterns, with extreme winds generated by microbursts and downbursts on the sub-100-meter scale, reaching at least EF1 intensity and, locally, reaching EF2 intensity. Observational analyses reveal that enhanced low-level southwesterly winds and sustained convergence zones along the mountainous areas facilitated moisture accumulation in Beijing’s western foothills 1–2 h before the storms moved downslope, with the Global Positioning System observing increased precipitable water vapor. The downslope movement of the storms essentially resulted from gust fronts interacting with mountain-foot convergence zones, triggering new convective storms that rapidly developed into a squall line with reflectivity levels exceeding 55 dB
Z within 18 min. Physical process analysis indicates that damaging winds in areas such as Bei’anhe were caused by downbursts embedded within cold pool-driven gust fronts. Extreme winds near Yuanmingyuan additionally involved a low-level γ-mesoscale vortex, whose path closely matched the severely damaged areas, demonstrating the direct impact of the vortex on localized wind intensification. At 1430 BJT, radar detected radial velocities reaching 53 m s
−1 (at an altitude of 0.38 km) following velocity de-aliasing, together with features resembling tornadic debris, albeit with a relatively weak echo intensity. Quantitative estimation of different physical processes suggests that cold pool outflow contributed approximately 20 m s
−1, whereas the low-level γ-mesoscale vortex and downbursts each enhanced near-surface winds by 15–18 m s
−1.