Unusual sferics observed at Agra

Abstract

Employing the experimental setup intended for whistler observations, a large number of unusual sferics have been recorded at the low latitude ground station Agra (geomagnetic latitude 18.09°N, longitude 152.21°E) during six months of observations between 01 November 2009 and 30 April 2010. The data include banded and narrow band sferics whose occurrences are found to be enhanced occasionally. The results have been examined as possible effects of lightning, solar flare, magnetic storms, and earthquake. The unusual enhancement of all types and those of banded structures have been found to correlate positively with X-ray events and magnetic storms, respectively. The banded and unusual structures of sferics have been interpreted in terms of specular reflection from a slab of enhanced ionization existing at the base of the ionosphere.