Physical and Meteorological Characteristics Associated with Lightning Ground Flashes: The National Lightning Detection Network and the Canadian Lightning Detection Network

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This grant supports a continuation of the analysis of lightning flash and stroke characteristics across the United States using data from the National Lightning Detection Network (NLDN). These data extend back to 1983. To the American data will be added data from the Canadian Lightning Detection Network (CLDN), which was established in 1997. The two networks combined comprise 187 sensors and provide data extending from 25 degrees to 60 degrees N latitude and from 50 degrees to 135 degrees W longitude. The number of recorded flashes on these networks exceeds 300 million. The data are used for characterizing different properties of cloud-to-ground lightning, including flash polarity, the number of flashes per unit area, the peak current, and stroke multiplicity. Studies are under way on the variation of these quantities with season and geographical location, and their dependence on local features such as mountains and cities. There is already evidence of increased flash rates over urban areas, explained perhaps by increased convection over heated cities or by microphysical effects of pollution aerosols. Other findings to now are that the highest peak currents are in the upper Midwest and the highest percentage of positive flashes to ground are along the West Coast of the United States. Physical explanations for these findings will be sought as part of the project.