Cloud-to-ground lightning downwind of the 2002 Hayman forest fire in Colorado

The Hayman forest fire occurred near Denver, burning similar to 138,000 acres during 8 June - 2 July 2002. It produced aerosol that filled the troposphere over Colorado, allowing an investigation of the effects of increased aerosol concentration on cloud-to-ground (CG) lightning polarity. Compared to climatological values over eastern Colorado, the 2002 fire period showed enhancements in satellite-derived aerosol optical depth ( AOD; up to 0.4 units greater), and the percentage of + CG lightning more than doubled in the domain average. However, spatial patterns were different in the fire's vicinity, with increases in AOD but not in + CGs. Denver soundings during the fire were compared to climatology, and showed environmental differences that are associated with increased + CG percentage, in particular higher cloud base and reduced warm-cloud depth. Thus, our findings provide only mixed support for the idea that smoke aerosols impact CG polarity, and suggest a possible link between drought conditions and increased + CG percentage.