The first observations of smoke-induced density currents originating from large wildfires are presented. Using a novel mobile Doppler lidar and additional in situ measurements, we document a deep (~ 2 km) smoke-filled density 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 these observations we show that the dynamics governing the spread of the smoke layer result from differential solar heating between the smoke-filled and smoke-free portions of the atmospheric boundary layer. A calculation of the theoretical density current speed agrees well with the observed propagation speed. Additional lidar and photographic documentation of other smoke-filled density currents demonstrate that these previously unknown phenomena are relatively common near large wildfires and can cause severe and unexpected smoke inundation of populated areas.
Neil Lareau and Craig Clements. "Cold Smoke: smoke-induced density currents cause unexpected smoke transport near large wildfires" Faculty Publications (2015). doi:10.5194/acp-15-11513-2015