Magnetosphere-Ionosphere Coupling Initiated at the Duskside Boundary Layer During Impulsive IMF Rotations

FARRUGIA, C. J.; GRATTON, F. T.; LUND, E. J.; SANDHOLT, P. E.; COWLEY, S. W. H.; MANN, I.; WATERMANN, J.; VILJANEN, A.; YUMOTO, K.

Beijing, China

Congreso; Western Pacific Geophysics Meeting; 2006

Observations from ACE, Wind, Cluster, FAST and ground magnetometers, complemented by theory, are presented to illustrate various aspects of Magnetosphere-Ionosphere (M-I) coupling during an event characterized by a sequence of interplanetary directional discontinuities (DDs) impinging on the magnetopshere. The Cluster spacecraft spent several hours on an outbound crossing of the duskside boundary layer at  ~30° MLAT, crossing in an almost radial direction.  This long duration came about  because the magnetopause (MP) was slowing expanding at the same time. The IMF rotated northward.  This rotation was, however, interjected by several abrupt and simultaneous east-west rotations of the field and flow. We focus on one such impulsive change, and show it to be simultaneously a TD and a vortex sheet with the field and flow executing a large rotation from west to east. Two wave types were seen at the magetopause, during and after the TD impinged on it. The attendant MP motions elicited large effects on the geomagnetic field, setting upstanding Alfven waves on resonating shells. Compressible calculations confirm the presence of MP surface waves of Kelvin-Helmholtz origin, in addition to the other undulatory motions of large amplitude. The continuous ground coverage from magnetometer arrays and radars allow us to document the ionospheric imprint of this activity. This work extends prior work by Kauristie et al., (2001) and Lund et al., (2004).