ACTUAL PROBLEMS OF THUNDERCLOUD ELECTRODYNAMICS

摘要

The electrodynamics of a thunderstorm cloud (TC) is considered with recircula-tion and multi-flow motion of charged cloud particles taken into account. In this consideration, the TC large-scale electric field is generated due to the charge separation during the convection of air and goes through oscillation phases during the initial and decaying stages of the TC. These oscillations explain qualitatively the observed behavior of TC electric fields. The multiflow character of convection introduces new important features of electric field generation in a TC. Multiflow convection is unstable and leads to the generation of slowly varying small-scale electrostatic fields with wavelength from ～ 1 / 100 m. The amplitude of these electrostatic fields can reach the conventional breakdown value. Such instability can initiate intracloud micro-discharges at the preliminary stage of a lightning discharge and between separate lightning strokes. The development of instability scales with micro-discharges in a multiplicative way and can reach the percolation threshold for the electrical conductivity inside a TC. In this way, a drainage system for cloud space charges is formed, which initiates the leader channel of the lightning discharge. Another important process associated with the development of short-scale electric fields is the acceleration of relativistic electrons due to runaway breakdown. Unlike large-scale electric fields, slowly varying short-scale electric fields can support the acceleration of electrons in a large volume of a TC.