Journal cover Journal topic
Annales Geophysicae An open-access journal of the European Geosciences Union
Ann. Geophys., 29, 701-716, 2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.
27 Apr 2011
Observations of an auroral streamer in a double oval configuration
O. Amm1, R. Nakamura2, T. Takada3, K. Kauristie1, H. U. Frey4, C. J. Owen5, A. Aikio6, and R. Kuula6 1Finnish Meteorological Institute, Arctic research unit, P.O. Box 503, 00101 Helsinki, Finland
2Space Research Institute, Austrian Academy of Sciences, Graz, Austria
3Kochi National College of Technology, Nankoku, Japan
4Space Sciences Laboratory, University of California, Berkeley, USA
5Mullard Space Science Laboratory, Dorking, UK
6University of Oulu, Oulu, Finland
Abstract. During the late evening and night of 14 September 2004, the nightside auroral oval shows a distinct double oval configuration for several hours after a substorm onset at ~18:45 UT. This structure is observed both by the IMAGE satellite optical instruments focusing on the Southern Hemisphere, and by the MIRACLE ground-based instrument network in Scandinavia. At ~21:17 UT during the recovery phase of the substorm, an auroral streamer is detected by these instruments and the EISCAT radar, while simultaneously the Cluster satellites observe a bursty bulk flow in the conjugate portion of the plasma sheet in the magnetotail. Our combined data analysis reveals significant differences between the ionospheric equivalent current signature of this streamer within a double oval configuration, as compared to previously studied streamer events without such a configuration. We attribute these differences to the presence of an additional poleward polarization electric field between the poleward and the equatorward portions of the double oval, and show with a simple model that such an assumption can conceptually explain the observations. Further, we estimate the total current transferred in meridional direction by this recovery phase streamer to ~80 kA, significantly less than for previously analysed expansion phase streamer events. Both results indicate that the development of auroral streamers is dependent on the ambient background conditions in the magnetosphere-ionosphere system. The auroral streamer event studied was simultaneously observed in the conjugate Northern and Southern Hemisphere ionosphere.

Citation: Amm, O., Nakamura, R., Takada, T., Kauristie, K., Frey, H. U., Owen, C. J., Aikio, A., and Kuula, R.: Observations of an auroral streamer in a double oval configuration, Ann. Geophys., 29, 701-716,, 2011.
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