Two‐dimensional interferometric positions of VHF lightning sources

Abstract

Using a new radio interferometric technique, we present observations of VHF lightning radiation source positions. The crossed base line interferometer provides the directions of arrival (azimuth and elevation) of VHF lightning radiation. Much flexibility exists in the choice of instrument parameters such as operating frequency and sampling interval. The present instrument operates at 34.3 MHz and provides an average position for every 2.5 μs of lightning radiation. Observations indicate that each 2.5 μs position should be attributed to a single discrete source in the sky. The positions of such sources define the temporal and spatial development of breakdown and rapid charge acceleration during the lightning flash. We have obtained VHF source positions correlated in time with electric field measurements. This allows us to identify the various processes occurring during a discharge and to compare the VHF phenomena with previously observed lightning phenomena. We have analyzed six flashes completely and portions of others. All six flashes contained ground strokes and two had intracloud discharges following the ground flash. We present data from three flashes that showed features common to the flashes we analyzed. The initial (preceding the first return stroke) and intracloud portions consisted of a large number of bursts of 20 μs average duration occurring on the average every 100 μs. The positions within each burst developed in a systematic, nearly linear, sequence with apparent speeds of ∼107 m/s. The relative positions from burst to burst drifted through the sky with speeds ∼105 m/s. In intracloud portions this drift was predominantly horizontal. In ground flashes the VHF sources drifted downward, in effect the leader for the first return stroke. They terminated at the return stroke.

Broad band radio interferometry for lightning observations

“…Narrow band radio interferometry has been implemented very successfully for lightning location studies [e.g., Hayenga, 1979Hayenga, , 1984Hayenga and Warwick, 1981;Richard and Auffray, 1985;Richard et al, 1986;Rhodes, 1989; Rhodes et al, 1994;Shao, 1993;Shao et al, 1995]. With this technique, phase differences between spatially separated antennas for an incident radiation wave are detected in a narrow band.…”

Broadband VHF sources locating system using arrival-time differences for mapping of lightning discharge process

“…The first one is the time of arrival (TOA) technique (Oetzel and Pierce, 1969;Proctor, 1971;Cianos et al, 1972;Murty and MacClement, 1973;MacClement and Murty, 1978;Proctor et al, 1988;Rison et al, 1999) that determines the location of radiations by taking differences between the times at which the radiation pulses are detected at each receiver. The other one is the narrowband interferometer system (Warwik et al, 1979;Hayenga and Warwik, 1981;Richard and Auffray, 1985;Laroche et al, 1994;Rhodes et al, 1994;Shao et al, 1995;Kawasaki and Yoshihashi, 2000) which uses frequency domain by taking differences of phases instead of times. Both methods are operated at a fixed frequency in VHF/ UHF range with a narrowband.…”

VHF broadband digital interferometer

“…When the phase difference goes through more than one cycle in a high-frequency component, there is the possibility of a fringe ambiguity [4][5][6]. We remove the ambiguity using the feature that the phase difference should be linearly dependent on frequency.…”