Effect of Pollution from Central American Fires on Cloud-to-Ground Lightning in the Spring of 1998

In the spring of 1998, numerous Central America fires produced aerosol particles that were advected into the central plains of the United States. The effects of the fires continued from approximately April 9 through June 11. The most intense smoke concentration was on May 8 as seen from a NASA shuttle mission. Characteristics of cloud-to-ground (CG) lightning for April through July 1998 were compared to lightning characteristics from 1995-1997 for the same months. Several significant differences are noted. The percentage of positive flashes increased by a factor of two. Median peak currents have been calculated for both positive and negative flashes. For negative flashes, the median peak current decreased during the fire period. For positive flashes, the median peak current increased for June only. Mean multiplicity values, or the number of strokes per flash, were calculated. Positive flash multiplicity did not change. Mean multiplicity for negative flashes, however, changed dramatically. For a region including Texas, Oklahoma, Kansas, and Louisiana multiplicity values for negative flashes decreased from 2.4 to 1.0 - 1.4 for April through June. Further studies should reveal the relation between the effect of pollution and aerosol size on the characteristics of CG lightning.