Lightning ground flash measurements over the contiguous United States: 1995-97

Cloud-to-ground lightning data have been analyzed for the years 1995-97 for the contiguous United States for total flashes, positive hashes, the perce ntage of positive lightning, peak currents for negative and positive lightn ing, and for negative multiplicity. The authors examined a total of 75.8 mi llion flashes divided among the three years, 22.7 million (1995), 26.2 mill ion (1996), and 26.9 million (1997). The highest flash densities, uncorrect ed for detection efficiency, occur in Louisiana and Florida, typically exce eding 11 flashes km(-2) on a grid scale of 0.2 degrees. Positive flash dens ities exceed 1.1 flashes km(-2) in Florida, Louisiana, and an area overlapp ed by the states of Tennessee, Mississippi, and Kentucky. The monthly perce ntage positive lightning ranges from 6.5% (Jury 1995) to 24.5% (January 199 6). The annual percentage of positive lightning is 9.3% (1995), 10.2% (1996 ), and 10.1% (1997). Areas of positive lightning greater than 25% occur fro m the Canadian border as far south as Kansas, along the West Coast, as well as Maine. The median negative peak currents are approximately 20 kA from J anuary through November, jumping to 24 kA in December. The median positive peak currents are highest in February (25 kA) and decrease to a minimum in July (15 kA). Median negative peak currents are high along continental coas tal areas, particularly the West Coast. Mountainous regions appear to have lower median negative peak currents, on the order of 18 kA. Median positive peak currents exceed 40 kA in the upper Midwest, but are less than 10 kA i n Louisiana and Florida. The mean flash multiplicity appears to increase wi th decreasing latitude in the eastern half of the United States.