The Ørsted Satellite Project

Christiansen, F. (1), V.O. Papitashvili (2), and T. Neubert (1)

1. Solar-Terrestrial Physics Division, Danish Meteorological Institute, Lyngbyvej 100, DK-2100 Copenhagen, Denmark. Fax.: +45 39 15 74 60 E-mail: fch@dmi.dk.


2. Space Physics Research Laboratory, University of Michigan, Ann Arbor, MI 48109, USA.

Abstract. In this paper, we report on high-precision observations of high latitude field-aligned currents (FAC) detected by the Danish satellite Ørsted, now more than one year in operation. Because of a slow drift in local time of the satellite orbit through the "noon-midnight" sector, we were able to study the seasonal dependence of the dynamic properties of the dayside and nightside field-aligned current systems over the northern and southern polar caps. We find an average over-the-pole distance between dayside and nightside currents of 36°-37° during equinox, 37°-38° during winter, and 32° during summer. The decrease in the summer polar cap is caused by a shift of both daytime and nighttime current systems to higher magnetic latitudes. For comparison, the dawn-dusk cross-polar distance of the Region 1/Region 2 field-aligned currents has been determined from high-precision data observed by MAGSAT, a satellite flown in 1979-1980 in a "dawn-dusk" orbit. The latter results show that the dawn-dusk distance between R1/R2 currents exhibits little seasonal dependence and amounts to ~34° for all seasons in both polar caps.