HR: 08:00h
AN: AE31A-01 INVITED     [PDF]
TI: Lightning Initiation by Runaway Air Breakdown
AU: * Roussel-Dupr‚, R A
EM: bobrd@lanl.gov
AF: Los Alamos National Laboratory, Group EES-2, Mail Stop F665, Los Alamos, NM 87545
AU: Symbalisty, E M
EM: emds@aftac.gov
AF: Los Alamos National Laboratory, Group EES-2, Mail Stop F665, Los Alamos, NM 87545
AU: Gurevich, A V
EM: alex@lpi.ru
AF: P.N. Lebedev Institute of Physics, Russian Academy of Sciences, Leninsky Prospect, 53, Moscow, 117924 Russian Federation
AU: Zybin, K
EM: zybin@lpi.ru
AF: P.N. Lebedev Institute of Physics, Russian Academy of Sciences, Leninsky Prospect, 53, Moscow, 117924 Russian Federation
AU: Babich, L
EM: kay@sar.ru
AF: Russian Federal Nuclear Center-VNIIEF, Mira street, 37, Sarov, 607190 Russian Federation
AU: Kutsyk, I
EM: kay@sar.ru
AF: Russian Federal Nuclear Center-VNIIEF, Mira street, 37, Sarov, 607190 Russian Federation
AB: The maximum macroscopic electric fields measured in thunderstorms are generally found to exceed the threshold for runaway breakdown and lie below the threshold for initiating conventional breakdown. In order for the conventional process that has been studied extensively in the laboratory to initiate lightning discharges it is necessary therefore to invoke the existence of field enhancements (e.g. around water droplets) in the thunderstorm electrical environment. On the other hand, the recent measurements of penetrating radiation in association with the leader activity that precedes a return stroke in natural lightning and triggered lightning have confirmed the importance of runaway breakdown in lightning discharge physics as a whole. In this talk we examine the potential role of runaway breakdown in initiating lightning. Several mechanisms are proposed including the initiation of an intra-cloud lightning discharge by an extensive energetic ($>$10$^{15}$ eV) cosmic ray shower (CRS). The results of first principles, fully electromagnetic, 2-D simulations of these various initiation mechanisms are presented. Conventional breakdown is found to develop in the field enhancement that occurs at the tip of a propagating positive streamer initiated by the combination of runaway breakdown and a CRS. The radio frequency emissions calculated for these discharges resemble the narrow bipolar pulses that have been associated with lightning initiation. The theory of runaway breakdown will be contrasted against conventional breakdown and the implications of our results for lightning initiation will be discussed.
DE: 0320 Cloud physics and chemistry
DE: 0342 Middle atmosphere--energy deposition
DE: 0619 Electromagnetic theory
DE: 2104 Cosmic rays
DE: 2116 Energetic particles, planetary
SC: Atmospheric and Space Electricity [AE]
MN: 2003 Fall Meeting