Asymmetric ring current at twilight local time

Ogo 2 rubidium vapor magnetometer measurements were compared with surface magnetic observatory data collected during three magnetic storms, March 13–15, 22–25, and 28–29, 1966. These comparisons were made at local times near the dawn-dusk meridian for dip latitudes less than 45°. The sources of low-latitude and midlatitude field depressions (Dst and Ds) are not in the ionosphere, but are located beyond the altitude of the satellite (413–1510 km). The resulting disturbance is longitudinally nonsymmetric; the disturbance at dusk is greater than the disturbance at dawn.