The possible physical mechanism of initiation and growth of lightning

Abstract

According to insight on the liquid drop instability as for the surface electric discharge it is shown that the initiation of lightning discharge can be related to instability of negatively charged water drops in an external electric field. In the total intracloud field (quasiconstant and chaotically varied in time) the large charged drops and the watered ice crystals (R > 30 μm) can be unstable and start to emit highly-dispersed (r ⩽ 0.01R) heavily charged drops, unstable by the Rayleigh criterium of stability. These drops break down in a period of time of the order of tens of intrinsic oscillation periods ~10−6 s, emitting ~100 more smaller drops. The field strength of intrinsic charges near the drop surface is sufficiently large for effective autoelectron emission (108–109 V/cm). Due to the total electric field near the surface of the droplets the emitted electrons initiate electron avalanches whose characteristic linear sizes are determined by the dimensions of the space region where the coefficient of electron multiplication exceeds unity. The lifetime of one avalanche is ~10−7 s. The same is the time interval between the consistent emission of two electrons by a drop. A transit of the series of consistent avalanches following the same track leads to the development of a plasma frame in the avalanche track. The overlap of the frames of adjacent avalanches in the vicinity of a group of closely located drops gives rise to formation of a plasma region (PR).The PR polarization in an intracloud quasiconstant electric field E0 and its growth along E0 (which is controlled by electric charges arriving into the PR from the surrounding space and originates from the charged drops instability as well as development of the ionization-avalanche processes near the PR tops) enables one to explain the phenomenon of discharge channel branching and propose a physically clear mechanism of collection of negative electric charges from separate drops carried out by lightning. A stepped leader is treated as a result of the ion-sound waves drive in the discharge channel plasma.