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. Specifically, we examine whether positive CG (+CG) flashes are favored in smoky environments. Aerosol optical depth (AOD) over eastern Colorado during the fire was tracked by satellite, and was compared to climatological observations. In addition, CG lightning during the fire was compared to climatology. The 2002 period showed enhancements in AOD and the percentage of +CG lightning. 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 enhanced +CG lightning. Thus, our findings provide only mixed support for the idea that smoke aerosols impact CG polarity.