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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 15, 11513-11520, 2015
https://doi.org/10.5194/acp-15-11513-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
20 Oct 2015
Cold Smoke: smoke-induced density currents cause unexpected smoke transport near large wildfires
N. P. Lareau and C. B. Clements Fire Weather Research Laboratory, San José State University, San José, CA, USA
Abstract. 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.

Citation: Lareau, N. P. and Clements, C. B.: Cold Smoke: smoke-induced density currents cause unexpected smoke transport near large wildfires, Atmos. Chem. Phys., 15, 11513-11520, https://doi.org/10.5194/acp-15-11513-2015, 2015.
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Short summary
This paper presents first observations of smoke-induced density currents, which are a boundary-layer flow phenomenon resulting from radiative shading by wild fire smoke. Our analysis uses a mobile Doppler lidar to reveal the anatomy and evolution of one such density current in northern California. The results show that these density currents can flow counter to the ambient wind and spread over long distances (e.g. 25km), causing unexpected smoke impacts.
This paper presents first observations of smoke-induced density currents, which are a...
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