Articles | Volume 26, issue 12
Ann. Geophys., 26, 3967–3977, 2008
Ann. Geophys., 26, 3967–3977, 2008

  05 Dec 2008

05 Dec 2008

Ionospheric signatures during a magnetospheric flux rope event

L. Juusola1, O. Amm1, H. U. Frey2, K. Kauristie1, R. Nakamura3, C. J. Owen4, V. Sergeev5, J. A. Slavin6, and A. Walsh5 L. Juusola et al.
  • 1Finnish Meteorological Institute, P.O. Box 503, 00101, Finland
  • 2University of California, Space Sciences Laboratory, Berkeley, CA 947207450, USA
  • 3Space Research Institute, Schmiedlstrasse 6, Graz, 8042, Austria
  • 4Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK
  • 5St. Petersburg State University, Petrodvoretz, 198504 St. Petersburg, Russia
  • 6Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA

Abstract. On 13 August 2002, during a substorm, Cluster encountered two earthward moving flux ropes (FR) in the central magnetotail. The first FR was observed during the expansion phase of the substorm, and the second FR during the recovery phase. In the conjugate ionospheric region in Northern Fennoscandia, the ionospheric equivalent currents were observed by the MIRACLE network and the auroral evolution was monitored by the Wideband Imaging Camera (WIC) on-board the IMAGE satellite. Extending the study of Amm et al. (2006), we examine and compare the possible ionospheric signatures associated with the two FRs. Amm et al. studied the first event in detail and found that the ionospheric footprint of Cluster coincided with a region of downward field-aligned current. They suggested that this region of downward current, together with a trailing region of upward current further southwestward, might correspond to the ends of the FR. Unlike during the first FR, however, we do not see any clear ionospheric features associated with the second one. In the GSM xy-plane, the first flux rope axis was tilted with respect to the y-direction by 29°, while the second flux rope axis was almost aligned in the y-direction, with an angle of 4° only. It is possible that due to the length and orientation of the second FR, any ionospheric signatures were simply mapped outside the region covered by the ground-based instruments. We suggest that the ground signatures of a FR depend on the orientation and the length of the structure.