Stratospheric Lightning over the 29-30 May 2012 Supercell Storm during DC3

Abstract:

On 29–30 May 2012, the Oklahoma Lightning Mapping Array, as part of DC3, observed the entire lifetime of a supercell storm that produced severe hail and a tornado in central Oklahoma until it rapidly dissipated after merging with a left-moving supercell storm near Oklahoma City. Previous conference presentations of data from 2320–0000 UTC have noted that flash rates increased to more than 100 min^-1 and updraft speeds in Doppler analyses increased to 55 m s^-1. Flash rates continued increasing to a peak of 400 min^-1 at 0045 UTC. This paper concerns data from 0101–0111 UTC, when flash rates had decreased to approximately 300 min^-1 and the lightning hole was dissipating, just before flash rates increased again as the storm drew near the left-moving supercell storm and merged with it. Between 0101 and 0111 UTC, an automated algorithm that grouped VHF sources into flashes (i.e., groups of VHF sources separated by > 200 ms or > 5 km from previous groups of VHF sources) identified several small flashes at approximately 19 km MSL, above the storm and a few tens of kilometers southeast of the overshooting storm top. A closer examination of these stratospheric “flashes” revealed that all were coincident in time with flashes at an altitude of 8–10 km MSL within the storm. In each of the two levels, most discharges had a horizontal extent of ≤5 km. Stratospheric discharges tended to overlap but extend east of the in-storm discharges and had substantially fewer VHF sources. However, all the VHF sources in the stratosphere clustered in time with bursts of VHF sources at 8–10 km MSL and avoided gaps between the bursts. Mapped VHF sources depicted no connecting channel between the two levels, so either a vertical connecting channel failed to be detected or the stratospheric discharges were triggered by flashes within the storm. Regardless, any chemical species (such as NO_x) produced by the upper discharges were injected directly into the lower stratosphere.