title: Runaway breakdown and hydrometeors in lightning initiation.
abstract: The particular electric pulse discharges are observed in thunderclouds during the initiation stage of negative cloud-to-ground lightning. The discharges are quite different from conventional streamers or leaders. A detailed analysis reveals that the shape of the pulses is determined by the runaway breakdown of air in the thundercloud electric field initiated by extensive atmospheric showers (RB-EAS). The high amplitude of the pulse electric current is due to the multiple microdischarges at hydrometeors stimulated and synchronized by the low-energy electrons generated in the RB-EAS process. The series of specific pulse discharges leads to charge reset from hydrometeors to the free ions and creates numerous stretched ion clusters, both positive and negative. As a result, a wide region in the thundercloud with a sufficiently high fractal ion conductivity is formed. The charge transport by ions plays a decisive role in the lightning leader preconditioning.
authors.affiliation: PN Lebedev Physical Institute, Russian Academy of Sciences, Moscow 119991, Russia. alex@lpi.ru
authors.forename: A V
authors.initials: AV
authors.lastname: Gurevich
authors.forename: A N
authors.initials: AN
authors.lastname: Karashtin