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

The Hayman forest fire occurred near Denver, burning ∼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.