Results of spatial and temporal characterization of the VHF‐UHF radiation of lightning

Abstract

A 300‐MHz interferometric imaging system has been used for the characterization of the VHF‐UHF electromagnetic radiation from lightning flashes. Results are presented, with emphasis on typical phenomenology, in particular through correlations with the electrical activity description from an E field sensor network. At the microsecond time scale the VHF‐UHF radiation appears impulsive, either as low rate pulsed emissions or as bursts of pulses. The low‐rate emissions (below 20 pulses/ms) are usually present during important intracloud charge transfers and correspond to spread out sources over distances of the order of 1 km. The bursts last from several hundred microseconds to a few milliseconds, and they are associated with highly organized propagations of sources in the 10 7 ‐m/s velocity range extending over distances of several kilometers. They appear in all phases of the lightning flash and are not associated with large charge transfers. Their spatial evolution and chronology with respect to the electrical phenomenology, in particular during precursor phenomena, indicate a decorrelation between electromagnetic phenomenology and the typical electrical phenomenology.