Solar cycle modulation of the constituents of geomagnetic field at Alibag

Abstract

Amplitudes of solar cycle modulation (SCM) in Sq range and the symmetric part of the disturbance field (DR) in H at Alibag, a low latitude station, are found to be comparable in magnitude but are nearly in phase opposition. The asymmetric part of the disturbance (SD) is noticed to undergo smaller modulation than that of DR. The wave forms corresponding to solar cycle in SD and DR are in phase opposition during morning hours and in phase in the evening hours, leading to a marked forenoon/evening asymmetry in the amplitude of cyclic modulation of the disturbance field. It is inferred that the amplitude of SCM of the geomagnetic field (H) around noon is primarily controlled by Sq, while that in the evening hours could be of disturbance origin.