Large Peak Current Cloud-to-Ground Lightning Flashes during the Summer Months in the Contiguous United States

Abstract

A clear association between large peak current cloud-to-ground lightning flashes of positive polarity and sprites and elves in the stratosphere and mesosphere has been previously demonstrated. This paper reports on the first climatology of large peak current cloud-to-ground (LPCCG) lightning flashes compiled from the U.S. National Lightning Detection Network. Analysis of almost 60 million CG flashes from 14 summer months (1991?95) reveals distinct geographic differences in the distribution of positive and negative polarity LPCCGs, arbitrarily defined as flashes with peak currents ≥75 kA. Large peak current positive CGs (LPC+CGs) are concentrated in the High Plains and upper Midwest, the region in which a large majority of optical sprite and elves observations have been obtained. By contrast, large peak current negative CGs (LPC?CGs) preferentially occur over the coastal waters of the Gulf of Mexico and the southeastern United States. A total of 1.46 million LPCCGs were found, of which only 13.7% were +CGs. Almost 70% of the LPC+CGs, however, occurred in the central United States (30°?50°N, 88°?110°W). The percentage of all LPCCGs that were positive approached 30% in the central United States compared to 4.5% for the remainder of the country. A +CG is 3.1 times more likely to exceed 75 kA than is a ?CG flash on a national basis. Yet in terms of absolute numbers for all ranges of peak current ≥75 kA, negative CGs are clearly dominant. For peak currents ≥75 and 200 kA, negative CGs outnumbered positive CGs by ratios of 6.4 and 4.1, respectively. In the central United States, however, during evening hours the number of LPC+CGs almost reaches parity with LPC?CGs. Average stroke multiplicity also exhibited regional differences. Over a half million negative CGs and over 1000 positive CGs were found with multiplicity ≥10.