oa A Ten-Year Lightning Climatology For The United States (1989-1998)

More than two hundred million cloud-to-ground lightning flashes have been recorded in the last ten years in the<br>continental United States. We have the first decadal climate of lightning that reveals year-to-year variations, but also<br>persistent features that repeat every year. Maximum flash densities occur in Florida, but also in the upper Midwest and<br>over the Gulf Stream east of the Carolinas. Relative minimums in flash density are observed over the mountains in the<br>west and over the Appalachian Mountains in the east. The dominant polarity of the charge brought to ground, termed<br>negative and positive lightning, varies with the season and latitude. The positive flash density appears to be a function of<br>geographic altitude, but the negative flash density is apparently not a function of geographic elevation. Explanations for<br>these observations will be proposed.