Cold Smoke: smoke-induced density currents cause unexpected smoke transport near large wildfires

摘要

The first observations of smoke-induced density currents originating from largewildfires are presented. Using a novel mobile Doppler lidar and additionalin situ measurements, we document a deep (~ 2 km) smoke-filleddensity current that propagates more than 25 km at speeds up to 4.5 m s?1 near a large forest fire in northern California. Based on theseobservations we show that the dynamics governing the spread of the smokelayer result from differential solar heating between the smoke-filled andsmoke-free portions of the atmospheric boundary layer. A calculation of thetheoretical density current speed agrees well with the observed propagationspeed. Additional lidar and photographic documentation of other smoke-filleddensity currents demonstrate that these previously unknown phenomena arerelatively common near large wildfires and can cause severe and unexpectedsmoke inundation of populated areas.