11A.1
Lightning relative to precipitation and tornadoes in a supercell storm during MEaPRS
Don MacGorman, NOAA/NSSL, Norman, OK; and D. Rust, O. van der Velde, M. Askelson, P. Krehbiel, R. Thomas, W. Rison, T. Hamlin, and J. Harlin
The MCS Electrification and Polarimetric Radar Studies (MEaPRS) field program was based in central Oklahoma in 1998. Data acquired by MEaPRS included data from a 10-cm polarimetric radar operated by the National Severe Storms Laboratory and from the lightning mapping array operated by New Mexico Institute of Mining and Technology. One of the storms observed by MEaPRS was a supercell storm that produced weak to strong tornadoes in the Oklahoma City area on June 13. This storm was positioned well for data collection by both the lightning mapping array and the polarimetric radar for roughly one hour, during which it produced tornadoes and large hail. The majority of cloud-to-ground flashes that occurred during this period were the anomalous flashes that lower positive charge to ground. Also, many of the cloud flashes that occurred in the upper part of the storm during this period appeared to discharge negative charge above positive charge, a polarity inverted from what is normally observed. Shortly after the storm moved beyond the range of three-dimensional lightning mapping data, it weakened and dissipated. The data show that trends in the number of VHF radiation sources near and within the mixed phase region of the storm were similar to trends for the mass and volume of graupel in this region. Graupel mass at still higher altitudes appeared unrelated to lightning. Trends were consistent with the hypothesis that increases in lightning lead severe weather occurrence, but increases in flash rates were neither as prominent nor as clearly associated with severe weather as those reported for Florida severe storms by other investigators, possibly because flash rates were very large throughout most of the period in the Oklahoma City storm. The rate of VHF emissions tended to increase at middle levels of the storm prior to tornadoes. Furthermore, the maximum height of VHF sources tended to increase shortly before or coincident with severe weather, in a pattern suggestive of updrafts and cloud turrets penetrating above the equilibrium level.
Session 11A, Lightning Studies
Wednesday, 14 August 2002, 4:30 PM-6:00 PM
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