VHF discharges in storm cells producing microbursts

An experiment was carried out in which 3-D mapping of VHF sources was compared to a 3-D description of the reflectivity and dynamics of associated cloud cells observed by a radar network. Data from 61 microbursts were analyzed and it was found that, in 93 pct. of the cases, electrical activity precedes outflow development. The results confirm that the peak in intracloud activity precedes the maximum value of the outflow

Propagation and Structure of Planar Streamer Fronts

Streamers often constitute the first stage of dielectric breakdown in strong electric fields: a nonlinear ionization wave transforms a non-ionized medium into a weakly ionized nonequilibrium plasma. New understanding of this old phenomenon can be gained through modern concepts of (interfacial) pattern formation. As a first step towards an effective interface description, we determine the front width, solve the selection problem for planar fronts and calculate their properties. Our results are in good agreement with many features of recent three-dimensional numerical simulations. In the present long paper, you find the physics of the model and the interfacial approach further explained. As a first ingredient of this approach, we here analyze planar fronts, their profile and velocity. We encounter a selection problem, recall some knowledge about such problems and apply it to planar streamer fronts. We make analytical predictions on the selected front profile and velocity and confirm them numerically. (abbreviated abstract)Comment: 23 pages, revtex, 14 ps file

Analyse spatio-temporelle du rayonnement VHF-UHF associé à l'éclair

The general features of the VHF-UHF radiation of lightning are studied both at the storm time scale and at the lightning discharge time scale. The evolution of the electromagnetic activity during the storm development is compared with the reflectivity and dynamics of the cloud given by a system of two radars. Some applications of this kind of study will be discussed in light of recent work devoted to the occurrence of thunderstorm microbursts related to the evolution of the electrical activity. In the second part of this paper, the detailed analysis of the electromagnetic radiation associated with an intracloud discharge is compared to laboratory experiments which enable to study the discharge mechanisms.Les caractéristiques générales de rayonnement électromagnétique VHF-UHF de l'éclair seront examinées tant au niveau global du développement de l'orage qu'à l'échelle d'une décharge isolée. L'étude de l'évolution de l'activité électromagnétique au cours de l'orage sera confrontée à une analyse radar des paramètres de la cellule orageuse (réflectivité, dynamique). Les perspectives ouvertes par ce type d'étude seront discutées à la lumière de travaux récents décrivant les phénomènes électriques précurseurs de l'apparition de forts cisaillements de vent au voisinage du sol. Par ailleurs, l'analyse détaillée du rayonnement associé à l'éclair intranuage sera approfondie grâce à la comparaison à des expériences de laboratoire permettant de préciser les différents mécanismes mis en jeu

Theorical modelling of the development of the positive spark in long gaps

Published in J Physics D : Applied Physics 27 (1994) 1252-1266SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.1994 n.143 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Simulation en laboratoire de l'attachement d'un leader à une structure flottante

The connection between an atmospheric lightning and an aircraft is studied by the way of inflight experiments. Unfortunately, these ones are not matched to the study of electrical discharges in the surroundings of the aircraft. For this reason laboratory experiments have been carried out to study the connection between long sparks and electrically floating structures. Two laboratory experiments give results concerning the physical process involved in the connection and show that data recorded during inflight experiments are representative of an ignition of the discharge on the aircraft itself.La connexion entre un éclair atmosphérique et un avion est étudiée grâce à des expériences en vol. Malheureusement, celles-ci sont mal adaptées à l'étude de la formation des décharges électriques à l'extérieur de l'appareil c'est pourquoi des expériences de laboratoire ont été entreprises pour étudier la formation et le développement des canaux de décharge lors de leur connexion avec des structures électriquement flottantes. Deux expériences de laboratoire présentées ici permettent de préciser la phénoménologie de la connexion et montrent en particulier que les signaux enregistrés sur avion sont caractéristiques d'un amorçage de la décharge à partir de la structure