Temporal Monitoring of VHF and LF Atmospherics and Their Relation to Lightning
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH
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Atmospheric discharges of various types emit electromagnetic radiation over a wide range of frequencies. VHF transients are associated with the discharges that occur during the preliminary charge separation and breakdown processes of lightning. Correlated VHF-LF activity emitted at relatively high magnitudes are normally attributed to lightnings powerful return stroke and recoil streamer discharges. This research hypothesized that VHF atmospherics precursors exist at least 1 minute or more before correlated VHF-LF transient activity return strokes or recoil streamers is detected during known lightning and thunderstorm periods. For 56 days, high-sampling-rate digitizers continuously monitored atmospheric conditions in VHF and LF bandwidths and measured the peak magnitude of transients as they occurred. The data was recorded in a computer file and used to characterize transient activity during various weather periods. The experimental results collected throughout confirmed lightning and thunderstorm intervals showed a significant increase in transient activity and that VHF atmospherics were detected on the average at least 3 minutes before any correlated VHF-LF transient activity was measured. In a few cases, the lead time was even greater when the initial VHF existed an average of at least 11 minutes before the onset of correlated VHF-LF.
- Atmospheric Physics
- Radiofrequency Wave Propagation