Observations of an auroral streamer in a double oval configuration

Amm, O.1, Nakamura, R.2, Takada, T.2, Kauristie, K.1, Frey, H. U.3, Owen, C.4, Aikio, A.5 and Kuula, R.5

1 Finnish Meteorological Institute, Helsinki, Finland
2 Space Research Institute, Austrian Academy of Sciences, Graz, Austria
3 University of California, Space Sciences Laboratory, Berkeley, USA
4 Mullard Space Science Laboratory, Dorking, UK
5 Department of Physical Sciences, University of Oulu, Oulu, Finland

During the late evening and night of September 14, 2004, the nightside auroral oval shows a distinct double oval configuration for several hours after a substorm onset at ~ 1845 UT. This is observed both by the IMAGE satellite optical instruments, and by the MIRACLE ground-based instrument network. While the two auroral regions are otherwise disconnected and slowly drifting equatorward with comparable speeds, at ~ 2117 UT an auroral streamer is detected by IMAGE over northern Fennoscandia, which connects the two regions for a few minutes. This streamer causes a distortion in the equivalent current patterns seen by the MIRACLE network which indictates that also current is transferred between the two regions. Further, the streamer moves over the EISCAT beams which allows us to deduce the electron density structures and conductances associated with it in detail. The magnetic footprints of the Cluster satellites are located at the streamer's eastern flank, where Cluster measures a bursty bulk flow in the magnetotail. We will compare in detail the electrodynamics and the ionosphere-magnetosphere coupling of this late recovery phase streamer with previously studied expansion phase and early recovery phase streamer cases.