Journal
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES
Volume 119, Issue 6, Pages 3134-3165Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/2013JD020217
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Funding
- Defense Advanced Research Projects Agency [HR0011-10-1-0059]
- National Science Foundation [AGS-1205727, ATM-0536950]
- U.S. Missile Defense Agency [HQ0147-08-C-0025]
- Div Atmospheric & Geospace Sciences
- Directorate For Geosciences [1205727] Funding Source: National Science Foundation
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The VHF Broadband Digital Interferometer developed by Osaka University has been improved to allow continuous sampling over the entire duration of a lightning flash and to utilize a generalized cross-correlation technique for determining the lightning source directions. Time series waveforms of 20-80 MHz signals received at three orthogonally located antennas are continuously digitized over multisecond intervals, as opposed to sequences of short-duration triggers. Because of the coherent nature of the measurements, radiation sources are located down into the ambient receiver and environmental noise levels, providing a quantum leap in the ability to study lightning discharge processes. When postprocessed using cross correlation, the measurements provide angular uncertainties less than 1 degrees and time resolution better than 1 mu s. Special techniques have been developed to distinguish between actual lightning sources and noise events, with the result being that on the order of 50,000-80,000 radiation sources are located for a typical lightning flash. In this study, two-dimensional interferometer observations of a classic bilevel intracloud flash are presented and combined with three-dimensional Lightning Mapping Array observations to produce a quasi 3-D map of lightning activity with the time resolution of the interferometer. As an example of the scientific utility of the observations, results are presented for the 3-D progression speed of negative leaders associated with intracloud K-leaders.
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