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 107‐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.

General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal Abstract. During a lightning strike to an aircraft in flight, the lightning channel becomes deformed in the airflow and displaced along the aircraft, a so-called swept stroke. The deformation and the displacement are caused by the interaction between the aerodynamic flow and the plasma properties of the channel together with the properties of the surface. The main part of the lightning current is a continuous current with a magnitude of hundreds of amperes and a duration of hundreds of milliseconds. The objective of this article is to analyse the properties of the lightning channel during this continuous current phase in order to parametrize them; this parametrization is used in a companion paper (Larsson et al J. Phys. D: Appl. Phys. 33 1876-83) for complete swept-stroke simulations. A model of the thermodynamic evolution of a lightning channel during its continuous current phase is developed and numerically solved. In this model, the channel is assumed to have axial symmetry. A quantitative analysis of the influence of failing axial symmetry is also included. The main conclusions are that the steady-state conditions are rapidly reached and that the channel can be considered to be a free-burning arc subjected to increased thermal losses due to transverse aerodynamic flow.

The tropical convection experiment COPT 81 (Convection Profonde Tropicale) was carried out near Korhogo (Northern Ivory Coast) during May and June 1981. The June 22 squall line was observed using meteorological and electrical equipment. The frontal part was characterized by a heavy precipitation core associated with strong convection. It was followed by a region of weak precipitation and a wide area of stratiform rain. The characteristic of this squall line resides in the two‐dimensional structure of the observed three‐dimensional wind fields, with intense convection ahead of the heavy precipitation core. Electrical measurements indicate that electrostatic field changes, at ground level, occurred in the weak precipitation zone and in the stratiform precipitation region. No particular electrical activity was observed in the most convective but shallow part of the squall line. A classical dipole structure appeared within the stratiform area. The stationary electrical structure was coherent with the stationary dynamics and precipitation pattern of the squall line.

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The main purpose of the experiments described here is the analysis of the mechanisms of radome protection with lightning diverters of various types and sizes. A high voltage arrangement and associated diagnostics have been implemented to perform a quantitative study of the inception and propagation mechanisms of the corona and leader discharges that precede the final breakdown. It is shown that ambient humidity plays a significant role on the discharge process and that the nature of the discharge initiated from the strip is very different depending on the strip type. Segmented strips are more likely to allow energetic discharges to propagate from an internal antenna leading to radome puncture.