Spatial and frequency characteristics of equatorial enhancement of geomagnetic field variations

Abstract

The spatial and frequency characteristics of the equatorial enhancement for several period bands from minutes range to Sq harmonics are established using geomagnetic data from upgraded/new networks that were operational during the International Equatorial Electrojet Year along the Indian and Brazilian sectors. In addition to the regular Sq harmonics and well-developed train of Pc5 pulsations, the periodic components in the period range of 20-160 min are isolated using the data adaptive singular spectrum analysis technique. Equatorial enhancement factor ranges between 3 and 5, both for magnetic fields associated with ionospheric dynamo or the processes that have their primary origin in magnetosphere. Examination of the spatial behavior of variations from equatorial to polar region revealed that magnetic fluctuations in equatorial region have bi-modal origin; related to the ionospheric dynamo and magnetospheric process, the latter resulting from almost instantaneous transmission of polar electric field to equatorial region. When these two sources operate independently, the magnetic fluctuations in equatorial belt in relation to that at low latitudes are enhanced roughly by a factor of 4±1 due to enhanced Cowling conductivity. However, when the two mechanisms work in an interactive coupled manner, they may account for the variability of the equatorial enhancement seen in individual cases.