Night‐Time Earth Currents Associated with the Daily Magnetic Variations

Abstract

The daily magnetic variations Sq are generally believed to arise from a system of electric currents flowing mainly in the sunlit part of the ionosphere. The motion of this system around the Earth following the Sun produces a system of induced Earth currents, which also contributes to the magnetic variations. Theory shows that, even if there are no appreciable ionospheric currents in the night hemisphere, there will nevertheless be induced Earth currents in this hemisphere. These currents will flow mainly along semicircles of latitude, their circuits being completed by meridianal flow near the boundary between the day and night hemispheres. The magnitude and distribution of these Earth currents in the night hemisphere are of importance in determining the correct base line from which to measure the magnetic variations at each station in any detailed study of the Sq field. Copyright © 1965, Wiley Blackwell. All rights reserved