Observation of whistlers and associated ionospheric parameters during St. Patrick’s Day storm at low Latitude, Varanasi

Abstract

The paper presents the analysis of a large number of whistlers recorded during the St. Patrick's Day geomagnetic storm (17–23 March 2015) at Indian low latitude ground station Varanasi (geomag. lat. 140 55/ N, geomag. long. 1530 54/ E, L = 1.078). The increased occurrence of the recorded whistlers has been explained in terms of duct formations for the propagation of whistlers during the geomagnetic storm. The whistler’s activity extended up to the 19th March 2015 during the daytime. The ducted propagation of the recorded whistlers is supported by the analysis of the World-Wide Lightning Location Network (WWLLN) data. In this paper, the result showed that the occurrence time of causative sferics of more than 80 % was in good agreement with that of WWLLN lightning discharges within the propagation time. The origins of these lightning strikes are lying within a 500 km radius of the conjugate point of the Varanasi. By analyzing recorded whistlers, we have computed different ionospheric parameters of Earth. The dispersion for the nighttime whistlers lies between 11 and 15 sec½ whereas dispersion for the daytime whistlers lies between 12 and 25 sec½. The columnar ionospheric electron contents (TECs) computed for the recorded whistlers during nighttime lie between 25.47 TECU and 42.84 TECU whereas TECs of the daytime whistlers lie between 30.08 TECU and 125.48 TECU. These calculated columnar ionospheric electron contents are found to be of the same order of magnitude as the IRI-2012 modeled TEC over Varanasi and that of conjugate of Varanasi whereas GPS-TEC are found to be comparatively 8–15 TECU lower over Varanasi.