Determining the Horizontal Distance Distribution of Cloud-to-Ground Lightning
AIR FORCE INST OF TECH WRIGHT-PATTERSONAFB OH SCHOOL OF ENGINEERING
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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.