Observed multiscale dynamical processes responsible for an extreme gust event in Beijing

Abstract

Extreme wind gusts pose substantial threats to human safety and infrastructure, yet inadequate pre-onset observational constraints result in large uncertainties and inaccuracies in nowcasting and forecast. To address this gap, we conduct an in-depth investigation of a record-breaking surface gust event (wind speed > 35 ms-1) that occurred in Beijing during the early afternoon of 30 May 2024. We analyze the event's dynamical characteristics utilizing a high-resolution meteorological mesonet, which includes seven radar wind profilers (RWPs), a meteorological tower, automated weather stations, radar and satellite data. Multi-source observational analyses reveal that multicellular storm developed ahead of a convergence line, where northeasterly cold outflows collided with environmental southerly winds during their downhill propagation. Evaporative cooling drove the generation of extreme winds, reinforced by downward momentum transport and pressure gradient forcing. After reaching the plain, two convective segments subsequently merged into a well-organized squall system embedded with a midlevel mesovortex with intense rear-inflow jet. Low-level frontogenesis and shearing deformation provided favorable conditions for sustaining mesoscale convection, which in turn fueled small-scale turbulent energy processes. Turbulent inverse energy cascades-energy transfer from small to large eddies-intensified markedly as wind speeds increased. This study offers valuable insights into the multiscale dynamical processes governing convective evolution-captured by the RWP mesonet-that would otherwise remain inaccessible via other ways. Importantly, these findings support the validation of numerical simulation outputs, refinement of boundary-layer parameterization schemes in numerical weather prediction (NWP) models, and ultimately the enhancement of forecast skill for convection-associated extreme gust events.