Lightning Activity in a Hail-Producing Storm Observed with Phased-Array Radar

Abstract

This study examined lightning activity relative to the rapidly evolving kinematics of a hail-producing storm on 15 August 2006. Data were provided by the National Weather Radar Testbed Phased-Array Radar, the Oklahoma Lightning Mapping Array, and the National Lightning Detection Network.This analysis is the first to compare the electrical characteristics of a hail-producing storm with the reflectivity and radial velocity structure at temporal resolutions of less than 1 min. Total flash rates increased to approximately 220 min 21 as the storm's updraft first intensified, leveled off during its first mature stage, and then decreased for 2-3 min despite the simultaneous development of another updraft surge. This reduction in flash rate occurred as wet hail formed in the new updraft and was likely related to the wet growth; wet growth is not conducive to hydrometeor charging and probably contributed to the formation of a ''lightning hole'' without a mesocyclone. Total flash rates subsequently increased to approximately 450 min 21 as storm volume and inferred graupel volume increased, and then decreased as the storm dissipated.The vertical charge structure in the storm initially formed a positive tripole (midlevel negative charge between upper and lower positive charges). The charge structure in the second updraft surge consisted of a negative charge above a deep midlevel positive charge, a reversal consistent with the effects of large liquid water contents on hydrometeor charge polarity in laboratory experiments.Prior to the second updraft surge, the storm produced two cloud-to-ground flashes, both lowering the usual negative charge to ground. Shortly before hail likely reached ground, the storm produced four cloud-toground flashes, all lowering the positive charge. Episodes of high singlet VHF sources were observed at approximately 13-15 km during the initial formation and later intensification of the storm's updraft.

Kinematic and Microphysical Significance of Lightning Jumps versus Nonjump Increases in Total Flash Rate

“…Ice crystals and graupel/small hail contribute to electrification of thunderstorms and their typical fall speeds have been found to be ≤10 m s −1 (e.g., Dye et al 1983, Dye et al 1986, Musil et al 1986, Musil and Smith 1989. The literature also shows that lightning propagation typically avoids regions of peak updraft speed and intense updraft volume due to lower concentrations of precipitation size ice and a lack of available charge (e.g., Wiens et al 2005, Payne et al 2010, Emersic et al 2011, Calhoun et al 2013, Kozlowski and Carey 2014. These regions are referred to as "lightning holes."…”

Colorado Plowable Hailstorms: Synoptic Weather, Radar, and Lightning Characteristics

“…This is despite the fact that thunderstorm charging can be locally reduced in regions of wet hail growth (Saunders and Brooks 1992;Pereyra et al 2000;Emersic et al 2011), likely because of the reduced number of rebounding collisions between water-coated graupel and ice crystals. Lightning flash rate also has been found to be correlated with updraft strength, updraft volume, and graupel mass (e.g., Carey and Rutledge 1996;Wiens et al 2005;Tessendorf et al 2007;Deierling and Petersen 2008;Deierling et al 2008).…”

The role of dynamic transport in the formation of the inverted charge structure in a simulated hailstorm

“…Severe storms present a normal charge structure in the initial stages, and then the inverted charge structure appears as the storm evolves . Zheng et al (2009) and Emersic et al (2011) found that, during the stage of hail-fall, the charge structure of a storm is inverted and then returns to normal after the hail-fall has ended. The vertical charge structure initially displays a normal tripole structure; however, as the hail begins to fall, a negative charge region is found above a deep central positive charge region.…”