Extended Abstract (96K)P1.11
Cloud-to-ground lightning downwind of the 2002 Hayman forest fire in Colorado
Timothy J. Lang, Colorado State Univ., Fort Collins, CO; and S. A. Rutledge
The devastating Hayman forest fire occurred southwest of Denver in 2002. It started the afternoon of 8 June (local time), and by the time it was 100% contained on 2 July approximately 138,000 acres had been burned. During the fire's lifetime it produced substantial quantities of aerosol, which filled the atmosphere over northeastern Colorado. This provided an opportunity to investigate the effects of forest fire smoke plumes and aerosol layers on cloud-to-ground (CG) lightning polarity; specifically, examining whether positive CG flashes are favored in smoky environments. Aerosol optical depth (AOD) over eastern Colorado during the Hayman fire was tracked with the MODIS instrument aboard the Terra satellite, and was compared to MODIS observations for the same time period in previous and subsequent years (2000-2004). In addition, CG lightning activity during the Hayman fire was tracked using the NLDN, and compared to the same time period in previous and subsequent years (1996-2004). In both datasets, 2002 showed large enhancements in AOD as well as the percentage of positive CG lightning over much of northeastern Colorado, relative to other years. However, the spatial patterns disagreed in fire's vicinity, with increases in AOD but little extra positive CG lightning. Moreover, 2002 featured overall less CG lightning, and the increase in positive CG percentage was mainly due to a major reduction in negative CG lightning (2002 was a drought year) than an increase in positive CG flash density. The 0000 UTC Denver soundings during the Hayman fire were compared to previous and subsequent years (1996-2004), and showed substantial environmental differences during 2002, particularly changes that are associated with enhanced positive CG lightning as found in other studies of environmental impacts on lightning. Thus, our findings provide only mixed support for the idea that smoke aerosols can impact CG polarity. Moreover, our results point to an intriguing possibility that the drought environments often associated with forest fires may themselves be conducive to enhanced positive CG production by thunderstorms.
Poster Session 1, Advances in Technology and Operational Utility of Lightning Data
Monday, 30 January 2006, 2:30 PM-4:00 PM, Exhibit Hall A2
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