Self-Consistent Model of Low- and High-Frequency Electromagnetic Emission of Compact Intracloud Discharges

Electromagnetic emission at the preliminary and main stages of compact intracloud discharge (CID) is examined in the framework of recently developed fractal model [1]. CID is considered as a result of electric coupling of two bipolar streamer-type discharge structures previously developed in regions of strong inhomogeneous electric field. To estimate electromagnetic emission of the discharge, tree-like current systems at the preliminary and main stages were represented as a sum of linear mean component and numerous small-scale constituents corresponding to initial breakdowns between the neighboring cells of the discharge domain. Mean linear currents are considered as effective sources of VLF/LF emission. Electrostatic, induction, and radiation electric field components at different distances from CID are calculated taking into account specific features of mean currents at both stages of the discharge. It is shown that, at the preliminary stage, only electrostatic component of the mean current field can be detected, whereas at the main stage all the above components can be observed confidently. Radiation electric field of mean current at the main stage in far zone represents a typical narrow bipolar pulse (NBP). Dependence of NBP profile on the discharge length and current pulse velocity is analyzed. It is shown that due to bi-directional expansion of mean current the bipolar pulse remains narrow in wide range of the discharge parameters. The small-scale linear currents corresponding to formation of new conducting channels of the discharge are considered as effective sources of HF/VHF emission. Radiation electric field of whole discharge structure at any stage of CID is a sum of contributions of small-scale breakdown currents. It is shown that HF/VHF emission at the preliminary stage is negligible as compared to the emission at the main stage, when a powerful narrow burst of the high-frequency emission forms. It is shown that the burst of HF/VHF emission correlates well with initial peak of NBP, and spectrum of the burst corresponds well to power law with an exponent between -2 and -1. [1] Iudin, D.I., and S.S. Davydenko (2015) Fractal model of a compact intracloud discharge. I. Features of the structure and evolution. Radiophysics and Quantum Electronics, Vol.58, No.7, pp.477-496, doi:10.1007/s11141-015-9621-2