Unusual Multiflash Whistlers at Low Latitudes

Abstract

Employing Haselgrove equations and a diffusive equilibrium model of the ionosphere, ray-tracing computations are carried out to explain the propagation characteristics of unusual type of multiflash whistlers recorded in the course of routine observations at low latitude whistler ground station, Nainital. The origin of these whistlers is explained in the following manner. They are caused by electromagnetic waves which are radiated from three successive return strokes of a lightning discharge or from the return strokes of three different lightning discharges occurring within 70 msec at slightly different places. These waves then penetrate the ionosphere at three different entry points and propagate towards opposite hemisphere in the whistler mode. Ultimately, they are received at the ground; giving rise to three peculiar whistler traces with different lower and upper cutoff frequencies which are explained in terms of the deviation of their ray paths from their respective whistler bunches.