NWC REU 2001
May 28 - August 3



A Relationship Between Surface Equivalent Potential Temperature and Dominant Lightning Polarity

Nettie Lake and Don MacGorman



Several studies have indicated that the dominant polarity of a thunderstorm may predict the severity of the thunderstorm. This study examines the differences in the location of thunderstorms dominated by positive cloud-to-ground lightning (initially positive storms) and of thunderstorms dominated by negative cloud-to-ground flashes (negative storms) relative to a surface equivalent potential temperature (theta-e) ridge. Previous studies suggest that a surface theta-e maximum separates initially positive storms on the upstream side of the ridge from negative storms on the downstream side. This study found that most initially positive storms form on the side of increasing theta-e relative to storm motion. Initially positive storms will usually cross the ridge axis and become dominated by negative cloud-to ground flashes. Other initially positive storms move adjacent to the ridge axis and remain positive. Some initially positive storms do not form near a theta-e ridge. Negative storms were thought to form downstream of a theta-e maximum, but this study found otherwise, as only 17% of negative storms examined formed downstream of the maximum. Nearly equal amounts of negative storms cross the axis, move adjacent to it, or do neither. Very few negative storms reversed dominant polarity, and if they did, it was during the final stages of the storms' duration.

Paper available upon request.