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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 20, issue 5
Ann. Geophys., 20, 629–637, 2002
https://doi.org/10.5194/angeo-20-629-2002
© Author(s) 2002. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 20, 629–637, 2002
https://doi.org/10.5194/angeo-20-629-2002
© Author(s) 2002. This work is distributed under
the Creative Commons Attribution 3.0 License.

  31 May 2002

31 May 2002

Monitoring magnetosheath-magnetosphere interconnection topology from the aurora

P. E. Sandholt1 and C. J. Farrugia2 P. E. Sandholt and C. J. Farrugia
  • 1Department of Physics, University of Oslo, Oslo, Norway
  • 2Space Science Center, University of New Hampshire, Durham, New Hampshire, USA
  • Correspondence to: P. E. Sandholt
  • (p.e.sandholt@fys.uio.no)

Abstract. A strong southward rotation of the IMF (BZ from 5 to -6 nT in ~ 20 s) on 4 January 1995 caused an abrupt reconfiguration of midday aurorae and plasma convection consisting of the following: (1) the red-line aurora associated with magnetosheath plasma transfer at the low-latitude magnetopause appeared at the same time that (2) the green-line aurora from precipitating energetic plasma sheet particles equatorward of the cusp (near the open-closed field line boundary) weakened visibly and shifted equatorward, (3) the high-latitude aurora during the previous northward IMF, which is associated with lobe reconnection, persisted briefly (3 min) and brightened, before it disappeared from the field-of-view, (4) the activation of a strong convection bay (DPY current) at cusp and sub-cusp latitudes when the field turned strongly south, (5) a distinct wave motion of the plasma sheet outer boundary, as inferred from the aurora, which correlates closely with Pc 5 magnetic pulsations. Our interpretation of the dramatic reconfiguration is that reconnection poleward of the cusp coexisted briefly with reconnection at sub-cusp latitudes. The latter provided a magnetic field connection which enabled, on the one hand, magnetosheath particles to enter and cause the red-line cusp aurora, and on the other hand, allowed for magnetospheric energetic particles to escape and weaken the outer plasma sheet source of the green-line emission. The coexistence of the two cusp auroras reflects the time required for one field line topology to replace another, which, under the prevailing high speed wind ( ~ 650 km/s), lasts ~ 3–4 min. The motion of open flux tubes propagating from equator to pole during this transition is traced in the aurora by a poleward moving form. The waves on the outer boundary of the plasma sheet are most likely due to the Kelvin-Helmholtz instability. The study illustrates the ability of local auroral observations to monitor even a global change in magnetospheric magnetic topology.

Key words. Magnetospheric Physics (auroral phenomena; magnetopause, cusp, and boundary layers; solar wind-magnethoshere interactions)

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