Lightning Flashes in Alabama Tornadic Supercells on 27 April 2011

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Wednesday, 7 January 2015
Jerome B. Blechman, SUNY, Oneonta, NY

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On 27 April 2011, a powerful storm system moved through the southeast region of the U.S. Northern Alabama and Mississippi experienced numerous tornadic supercell thunderstorms. Almost all supercells contained mesocyclones, some with very strong horizontal wind shear. All were prolific lightning producers. Since current theories of lightning generation depend on hydrometer collisions or near-collisions for charge exchange, an hypothesis was proposed that adding horizontal wind shear could have assisted in charge separation. Lightning flash data from the National Lightning Detection Network, supplied by Vaisala Inc., was superimposed on radar reflectivity and radial velocity maps from NCDC to test the hypothesis. It was assumed that increased charge separation would result in more flashes near the mesocyclone centers. The results showed that lightning flash densities were not biased closer to the mesocyclone centers. In fact, the patterns were very similar to those found in prior studies on weaker, often isolated supercells. Therefore, the hypothesis that the strength of horizontal wind shear in this organized cluster of tornadic supercells affected the patterns of lightning flashes was rejected.