VHF Broadband Interferometer Observations in Oklahoma
Abstract
The New Mexico Tech VHF Broadband Interferometer was operational at the El Reno Regional Airport in Oklahoma between April 27 and June 30 of 2018. This location coincided with the northwest side of the central Oklahoma 3D Lightning Mapping Array. The interferometer utilized three 13-inch flat plate VHF antennas (15-87 MHz bandwidth) arranged in an equilateral triangle with 80 meter baselines. A fast antenna was simultaneously sampled with the VHF at 180 MHz and 16-bit depth. A total of 36 TB of interferometer data was collected from over 24,000 lightning flashes. The parent storms varied widely from high flash-rate supercells and mesoscale convective systems to lower flash-rate isolated cells.
Of particular interest are fast breakdown events which are known to produce narrow bipolar events (NBEs) at the onset of some flashes. A significant number of NBEs associated with a supercell storm on May 2nd had precursor activity 10's to 100's of microseconds prior to the NBEs. Such NBE precursor activity was not seen in the prior 2016 and 2017 research campaigns conducted in Florida where NBEs are ubiquitous. Many of these supercell NBEs were isolated and composed of fast negative breakdown and this was also frequently observed in Florida. An interesting manifestation of fast positive breakdown (FPB) was observed in a hybrid IC-CG flash on June 7th. The flash began as a relatively ordinary bilevel IC which spawned a negative leader to ground about 450 milliseconds into the flash. The return stroke (RS) was followed a millisecond later by a FPB event which propagated horizontally and then up into the upper levels of the flash. While FPB had been previously documented to follow some negative CG RSs [Shao et al., J. Geophys. Res., 100, 1995], this FPB had an unprecedented long duration of over half a millisecond. There also was a slow field change associated with the FPB with superimposed large pulses which rivaled the amplitude of the preceding RS. The FPB followed a channel which was illuminated by a K-change of negative breakdown polarity about a tenth of a second earlier, though it was much brighter at VHF than that earlier K-change. It also had the unusual characteristic of appearing to pause and restart, though this may be due to a varying velocity and a VHF brightness which is a strong function of that velocity.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMAE11A..02R
- Keywords:
-
- 3304 Atmospheric electricity;
- ATMOSPHERIC PROCESSESDE: 3314 Convective processes;
- ATMOSPHERIC PROCESSESDE: 3324 Lightning;
- ATMOSPHERIC PROCESSESDE: 3329 Mesoscale meteorology;
- ATMOSPHERIC PROCESSES