Danyal Petersen

Simulating electrodeless discharge from a hydrometeor array

The objective of this research was to test, by means of an experiment in a high-voltage laboratory, the effect of an array of hydrometeors on the processes involved in the streamer-leader formation of lightning. Because the common types of hydrometeors present whenever lightning initiation in thunderstorms occurs are ice particles (graupel, hail, or ice crystals), we used, in this experiment, conductive particles similar to hail in size, with various spacing between them, but all under normal atmospheric pressure and room temperature. The laboratory array was suspended on dielectric threads in a uniform electric field of 1 MV m−1 in the middle of the gap between the high-voltage and ground electrodes. During the first phase of the experiment, we studied the formation of a bidirectional arc discharge from the array and the effects of the arrays size on the electrical characteristics and on the speed of development of the discharge. We continued with the same objectives in the second phase of the experiment, adding high-speed video observations with a recording speed of 10 Mfps, to observe all stages of the streamer-leader formation.

Large charge moment change lightning on 31 May to 1 June 2013, including the El Reno tornadic storm

On 31 May 2013, a line of severe tornadic thunderstorms (the El Reno event) developed during the local afternoon in central Oklahoma, USA. Within range of the Oklahoma Lightning Mapping Array, the evolution of the event can be separated into three distinct periods: an Early period (before 02:00 UTC on 1 June) when the storm consisted of discrete supercells, a Middle period (02:00–05:00 UTC) when the convection began merging into a linear feature and stratiform precipitation developed, and a Late period (after 05:00 UTC) featuring a mature mesoscale convective system (MCS). Each of these periods demonstrated distinct patterns in the large (>100 C km) charge moment change (CMC) lightning that was produced. During the Early period, large-CMC positive cloud-to-ground (+CG) lightning was produced in the convective cores of supercells. These flashes were small in area (typically 500 km2, >300 C km) in the developing stratiform, similar to typical sprite-parent lightning in MCSs. During the Late period, convective large CMC +CGs ceased and instead large-CMC negative CGs were produced in and near the MCS convection. These flashes neutralized charge both in convection as well as in adjacent stratiform and anvil precipitation. The results suggest that the CMC metric has potential applications for studying tropospheric weather.