Bead lightning formation

Abstract

Formation of beaded structures in triggered lightning discharges is considered in the framework of both magnetohydrodynamic ͑MHD͒ and hydrodynamic instabilities. It is shown that the space periodicity of the structures can be explained in terms of the kink and sausage type instabilities in a cylindrical discharge with anomalous viscosity. In particular, the fast growth rate of the hydrodynamic Rayleigh-Taylor instability, which is driven by the backflow of air into the channel of the decaying return stroke, dominates the initial evolution of perturbations during the decay of the return current. This instability is responsible for a significant enhancement of the anomalous viscosity above the classical level. Eventually, the damping introduced at the current channel edge by the high level of anomalous viscous stresses defines the final length scale of bead lightning. Later, during the continuing current stage of the lightning flash, the MHD pinch instability persists, although with a much smaller growth rate that can be enhanced in a M-component event. The combined effect of these instabilities may explain various aspects of bead lightning.

Equivalent of bead lightning in pulse discharge generated by runaway electrons in atmospheric pressure air

“…×èñëî ñîîáùåíèé î íàáëþäåíèè ÷å-òî÷íîé ìîëíèè ìàëî è íàìíîãî ìåíüøå, ÷åì ñîîáùåíèé î íàáëþäåíèè øàðîâîé ìîëíèè. Îäíàêî â íàó÷íîé ëèòåðàòóðå [1][2][3][4][5][6][7][8][9] ñóùåñòâóåò îáùåïðèíÿòîå ìíåíèå, ÷òî ÷åòî÷íàÿ ìîëíèÿ ÿâëÿåòñÿ îäíîé èç ôîðì àòìîñôåðíîãî ýëåêòðè÷åñòâà. ×àùå âñåãî îíà ïðîÿâëÿåòñÿ êàê ïóíêòèðíàÿ ñâåòÿùàÿñÿ ëèíèÿ èëè öåïî÷êà ïÿòåí, ïîÿâëÿþùàÿñÿ ìåaeäó îáëàêàìè ïîñëå îáû÷íîé ëèíåéíîé ìîëíèè.…”

“…Ïîÿâëåíèå ÷åòî÷íîé ìîëíèè â [8] îáúÿñíÿåòñÿ âîçíèêíîâåíèåì íåñòàáèëüíîñòåé â öèëèíäðè÷åñêîì ðàçðÿäå èç-çà àíîìàëüíîé âÿçêîñòè. Ðàñ÷åòû, ïðîâåäåííûå À.Ì.…”