Effect of near lightning discharges on a magnetometer

Abstract

During two thunderstorms at the beginning of the present monsoon, the recorded curves of the Copenhagen declination magnetograph recently installed at Alibag showed some characteristic features which on examination appear to be due to the effect of the magnetic field of the lightning discharge currents on the magnetometer. The magnetograms are reproduced in Fig. 1. The variations occurred between 2 hr. and 4 hr. and between 18 hr. and 22 hr. I.S.T. The storm was most intense in the second of the two intervals at about 20 hr. The magnetometer needle experienced a number of sudden kicks, and the subsequent oscillations gradually died down in 2-3 minutes. The maximum first deflection was about 1.5 mm.