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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. A11, 1372, doi:10.1029/2002JA009414, 2002

Seasonal and local time dependences of the interhemispheric field-aligned currents deduced from the Ørsted satellite and the ground geomagnetic observations

S. Yamashita

Department of Geophysics, Graduate School of Science, Kyoto University, Kyoto, Japan


T. Iyemori

Data Analysis Center for Geomagnetism and Space Magnetism, Graduate School of Science, Kyoto University, Kyoto, Japan


Abstract

The precise magnetic field measurements by the Ørsted satellite revealed a distinct spatial variation of the eastward component residual (ΔBφ) at mid and low latitudes on the dayside. This magnetic field variation was attributed to the interhemispheric field-aligned currents (IHFACs) at mid and low latitudes based on its comparison with ground geomagnetic field variations. These IHFACs were found to flow from the summer hemisphere to the winter hemisphere in the dawn sector, and from the winter hemisphere to the summer hemisphere in the noon and the dusk sectors. These IHFACs flip their direction not at equinoxes but in May and November. The current intensity of the IHFACs is largest not at solstices but in February and August. The ground-based geomagnetic field observations at 17 low latitude stations also support the seasonal dependence and local time distribution of the IHFACs.

Published 16 November 2002.

Index Terms: 2409 Ionosphere: Current systems (2708); 2431 Ionosphere: Ionosphere/magnetosphere interactions (2736); 2736 Magnetospheric Physics: Magnetosphere/ionosphere interactions; 2437 Ionosphere: Ionospheric dynamics; 2443 Ionosphere: Midlatitude ionosphere.

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Citation: Yamashita, S., and T. Iyemori (2002), Seasonal and local time dependences of the interhemispheric field-aligned currents deduced from the Ørsted satellite and the ground geomagnetic observations, J. Geophys. Res., 107(A11), 1372, doi:10.1029/2002JA009414.