The Ørsted Satellite Project

Yamashita, S., T. Iyemori, S. Nakano, T. Araki, and T. Kamei

1. IPGP, Graduate School of Science, Kyoto University, Institute of Geophysics, Solat-Planetary Electromagnetism Laboratory, Kyoto 606-8502, Japan. Fax: +81 75 722 7884. E-mail: yamasita@step1ku.kugi.kyoto-u.ac.jp

Abstract. The Oersted satellite was launched on February 23, 1999, and made precise magnetic measurement at low-altitudes near noon-midnight meridian for the period between April 1999 - January 2000. Adding to the expected signatures of the ring current, the Sq current and the equatorial electorjet in radial component (positive outward) and southward component, eastward component (eastward positive) shows distinct variations at mid- and low- latitudes. It has a negative trend in northward direction on the dayside, and a positive trend on the nightside. The slope has a high correlation with geomagnetic activity such as the ap index. This indicates the existence of the net Birkeland currents flowing into the ionosphere on the dayside, and flowing out on the nightside. The net currents seem to extend in wide LT range, and the center of the current on the dayside seems to be in the pre-noon sector.