Accession Number:

ADA370315

Title:

First Stroke Peak Current Characteristics for the United States

Descriptive Note:

Dissertation

Corporate Author:

TEXAS A AND M UNIV COLLEGE STATION

Personal Author(s):

Report Date:

1999-10-06

Pagination or Media Count:

290.0

Abstract:

The first stroke peak currents of over 105 million cloud to ground lightning flashes from 1995-1998 were analyzed over the continental Unites States U.S. landmass. The peak currents exhibit a variation based on season and geography, but positive flashes have different features than negative flashes. Several factors are considered when examining the peak current variations including latitudinal dependence, sensor separation in the National Lightning Detection Network, flash density variations, the percentage of positive flashes, and surface elevation. Two possible explanations for the peak current variations are changes in the return stroke velocity based on the atmospheric pressure and that the peak currents are dependent on the length of the lightning channel. Negative lightning demonstrated an inverse relationship between peak currents and the surface elevation. Positive peak currents and the percentage of positive flashes were strongly correlated. Further examinations of individual storm cases indicated fluctuations in the peak currents within larger storm systems. In the cases studied, the peak currents of the more intense flashes, or those with higher peak currents, demonstrated a periodicity on the order of one hour which is comparable to the lifetime of individual thunderstorm cells in the larger systems. This variation within storm systems seems to negate the possibility that the variations in the return stroke velocity make up the only contribution to peak current differences. The length of the lightning channel appears to have some influence on the strength of the peak currents.

Subject Categories:

  • Meteorology

Distribution Statement:

APPROVED FOR PUBLIC RELEASE