Determining the Horizontal Distance Distribution of Cloud-to-Ground Lightning

This research effort attempted to quantify what constitutes a safe distance when lightning is present. The method used in this research project groups lightning flashes into clusters using spatial and temporal constraints. However, not all flashes meet the time and distance criteria for clustering and remained outside of tile grouped flashes and as such are identified as isolated flashes. These isolated flashes are outliers in the data set, but are precisely the flashes that prove most dangerous. For this reason not only were the distances between each flash and cluster center studied, but also the distances between each isolated flash and its nearest neighboring flash. Distributions for both distances were studied for the continental U.S. by season. A common safety radius is 5 nautical miles, just less than 9.5 km. For all regions, anywhere from 16% to 35% clustered flashes occurred beyond 9.5 km from the cluster center and 71% to 81% of the isolated flashes occurred at distances beyond 9.5 km from the nearest flash. Cumulative frequency distributions of historical lightning data can be used to find the probability of having lightning at a particular distance. In this way an acceptable level of risk can be determined and then a "safe" distance found.Air Force Inst of Tech Wright-Patterson AFB Oh School of Engineering is the author of 'Determining the Horizontal Distance Distribution of Cloud-to-Ground Lightning', published 2000 under ISBN 9781423534112 and ISBN 1423534115.