The Ørsted Satellite Project

GEOMAGNETIC DISTURBANCES AT HIGH LATITUDES DURING VERY LOW SOLAR WIND DENSITY EVENT

Papitashvili, V.O. (1,2), C.R. Clauer (1), F. Christiansen (2), V.A. Pilipenko (2,3), V.A. Popov (4), O. Rasmussen (2), V.P. Suchdeo (1), and J.F. Watermann (2)

1. Space Physics Research Laboratory, University of Michigan, Ann Arbor, MI 48109, USA. E-mail: papita@umich.edu
2. Solar-Terrestrial Physics Division, Danish Meteorological Institute, Lyngbyvej 100, DK-2100 Copenhagen, Denmark.
3. Institute of Physics of the Earth, Moscow, Russia.
4. Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation, Moscow, Russia.

Abstract. In this letter we report geomagnetic observations over Greenland and Antarctica during May 11, 1999, when the solar wind almost disappeared. Greenland magnetometers show no magnetic activity in the nominal auroral zone but at higher latitudes magnetic disturbances reach ~200 nT; at the same time, ground conjugate magnetic observations in the southern polar region show much weaker disturbances, ~30-50 nT. These observations provide additional evidence that the cusp current system could be extended far to the dusk (dawn) sector in the northern (southern) polar region. This is consistent with observations made by the Ørsted satellite, which detected field-aligned currents near noon (cusp), over the northern geomagnetic pole, and in the nightside polar cap; however, almost no field-aligned currents are detected over the southern polar cap. We conclude that the low-density solar wind quieted phenomena at auroral latitudes (i.e., ”loading-unloading” processes); but the “directly-driven” convection processes observed over both the northern and southern polar caps were mainly unaffected by the significant inflation of the magnetosphere.