资源环境科技发展态势分析平台

Radar and satellite observations document the evolution of a destructive fire-generated vortex during the Carr fire on 26 July 2018 near Redding, California. The National Weather Service estimated that surface wind speeds in the vortex were in excess of 64 m/s, equivalent to an EF-3 tornado. Radar data show that the vortex formed within an antecedent region of cyclonic wind shear along the fire perimeter and immediately following rapid vertical development of the convective plume, which grew from 6 to 12 kmaloft in just 15 min. The rapid plume development was linked to the release of moist instability in a pyrocumulonimbus (pyroCb). As the cloud grew, the vortex intensified and ascended, eventually reaching an altitude of 5,200 m. The role of the pyroCb in concentrating near-surface vorticity distinguishes this event from other fire-generated vortices and suggests dynamical similarities to nonmesocyclonic tornadoes.

Plain Language Summary A tornado-strength fire-generated vortex devastated portions of Redding, California, during the Carr fire on 26 July 2018. In this study, satellite and radar observations document the evolution of the vortex, revealing similarities to tornado dynamics. A key factor in the vortex formation was the development of a fire-generated ice-topped cloud (i.e., a pyrocumulonimbus), which reached as high as 12 km aloft. The development of the cloud helped stretch the underlying column of air, thereby concentrating the rotation near the surface and causing the tornado strength winds, estimated at similar to 64 m/s. These observations will help forecasters and scientists identify, and potentially warn for, future destructive fire-generated vortices.