First observations of geomagnetic field variations within equatorial electrojet belt in Sri Lanka

Abstract

The daily variations of the geomagnetic horizontal (<i>H</i>),<i> </i>eastward (<i>Y</i>)<i> </i>and vertical (Z) fields at any equatorial electrojet station south of India have been described, for the first time, using the data from Peredinia, Sri Lanka (geogr. lat. 7.3°N, long. 80.6°E, dip lat. 1.3°S). An abnormal positive peak in the daily variation of the Z field at Peredinia (PRD) in the

forenoon hours, stronger in magnitude to corresponding abnormality in Z at Trivandrum (TRD), India has been detected. There is a remarkable correspondence between ΔZ at Trivandrum and Peredinia on day-today-basis, the variations being stronger at Peredinia than at Trivandrum. During a magnetic storm a sharp decrease of ΔZ is observed few hours before the maximum decrease of <i>H</i> at both PRD and TRD. These observations show, for the first time, that the induction anomalies in the equatorial electrojet region in Indo-Sri Lanka longitudes extend well beyond the southern tip of Indian Peninsula. The phenomenon of subsurface induction in Indian longitudes needs to be seriously reconsidered.