Global scale electrodynamic coupling of the auroral and equatorial dynamo regions

Abstract

The VHP backscatter radar observations on the equatorial electrojet at Thumba near Trivandrum (dip ~1°S) show that most of the bay-type disturbances in the surface geomagnetic field, with typical durations of 20–50 min, result from corresponding fluctuations of the overhead currents in the ionospheric dynamo region. The analyses of such events, using the VHF radar observations at Thumba and the magnetograms at different locations, have shown that the bay-type disturbances in the equatorial electrojet have their origin in corresponding disturbances in the auroral or polar dynamo region. Even some minor disturbances in the dynamo region electric fields at the auroral and polar latitudes are found to result in observable perturbations in the equatorial electrojet. The results of the detailed analyses of two disturbance events are presented in this paper. The simultaneity and the relative strengths of the estimated electric field perturbations during the disturbances at the auroral and equatorial electrojet latitudes indicate that the auroral and equatorial dynamo regions are coupled much more strongly than what has been suspected hitherto. Moreover, it is shown that the global scale current system associated with a bay-type disturbance undergoes large changes even within the duration of the disturbance. The implications of the above results in relation to the prevailing notions about the substorm-associated current systems are discussed.