Effect of Horizontal Gradients on the Propagation of Whistlers at Low Latitudes

Abstract

The possibilities of recordinl1. at ground stations, the unusual type of whistlers observed at low latitude ground stations, Gulmarg (geomag. lat., 24°10'N) and Nainital (geomaj lat., 19°1'N), India, are discussed. It is shown from the ray-tracing computations that a, small but suitable negative latitudinal I1radient of electron, density in the night-time, ionosphere at low latitudes is mainly responsible for non-ducted unusual type of whistlers to be observed on the ground. The propagation characteristics, including the upper and lower cut of frequencies of the low latitude whistlers observed on the ground, are also explained in terms of a P-L mode of propagation assuming a small negative latitudinal gradient of electron density in the ionosphere at low latitudes.