A Study of night time variations during magnetic storms at coastal Indian stations

Abstract

The sub-surface conductivity distribution of the Indian peninsula near Alibag, Annamalainagar and Trivandrum has been investigated by analysing storm time variations of the three components of the magnetic field. In this study only night time variations are considered in order to avoid the non-uniformity in the inducing field arising from the presence of electrojet in daytime. Spectral analysis is carried out to compute the auto and cross-spectra of the three components H,D and Z. for periods ranging from 32 to 210 minutes, These are then utilised to obtain the transfer functions and subsequently the induction vectors. From an earlier analysis of continuous data of 36 hours length or more, vectors were obtained that reflected the non-uniformity of the external inducing field in day time. A comparison of these with night time vectors showed significant differences for the stations, Annamalainagar and Trivandrum.