Variation with interplanetary sector of the total magnetic field measured at the OGO 2, 4 and 6 satellites

Abstract

Variations in the scalar magnetic field ( ΔB) from the polar orbiting OGO 2, 4 and 6 spacecraft are examined as a function of altitude for times when the interplanetary magnetic field is toward the Sun and for times when the interplanetary magnetic field is away from the Sun. In both cases, at all altitudes, the total field variations form a region of positive ΔB between about 22 hr and 10 hr MLT and a region of negative ΔB between about 10 hr and 22 hr MLT. This morphology is basically the same as that found when all data, irrespective of inter-planetary magnetic sector, are averaged together (Langel, 1974a, b). Differences in ΔB occur, both between sectors and between seasons, which are similar in nature to variations in the surface ΔZ found by Langel (1973). The altitude variation of ΔB at sunlit local times, together with variations in the vertical component ΔZ at the Earth's surface, demonstrates that the ΔZ and ΔB which varies with sector has an ionospheric source. Langel (1974b) showed that the positive ΔB region in the dark portion of the hemisphere is due to at least two sources, the westward electrojet and an unidentified non-ionospheric source (s). Comparison of magnetic variations between season/sector at the surface and at the satellite, in the dark portion of the hemisphere, indicates that these variations are caused by variations in the latitudinally narrow electrojet currents and not by variations in the non-ionospheric source of ΔB.