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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 19, issue 5
Ann. Geophys., 19, 487–493, 2001
https://doi.org/10.5194/angeo-19-487-2001
© Author(s) 2001. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 19, 487–493, 2001
https://doi.org/10.5194/angeo-19-487-2001
© Author(s) 2001. This work is distributed under
the Creative Commons Attribution 3.0 License.

  31 May 2001

31 May 2001

Excitation of transient lobe cell convection and auroral arc at the cusp poleward boundary during a transition of the interplanetary magnetic field from south to north

P. E. Sandholt1, C. J. Farrugia2, S. W. H. Cowley3, M. Lester3, and J.-C. Cerisier4 P. E. Sandholt et al.
  • 1Department of Physics, University of Oslo, P. O. Box 1048, Blindern, N-0316, Norway
  • 2Space Science Center, University of New Hampshire, Durham, NH 03824, USA
  • 3Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
  • 4Centre d’Etude des Environnements Terrestre et Planetaires, 4 Avenue de Neptune, 94107 Saint-Maur Cedex, France

Abstract. We document the activation of transient polar arcs emanating from the cusp within a 15 min long intermediate phase during the transition from a standard two-cell convection pattern, representative of a strongly southward interplanetary magnetic field (IMF), to a "reverse" two-cell pattern, representative of strongly northward IMF conditions. During the 2–3 min lifetime of the arc, its base in the cusp, appearing as a bright spot, moved eastward toward noon by ~ 300 km. As the arc moved, it left in its "wake" enhanced cusp precipitation. The polar arc is a tracer of the activation of a lobe convection cell with clockwise vorticity, intruding into the previously established large-scale distorted two-cell pattern, due to an episode of localized lobe reconnection. The lobe cell gives rise to strong flow shear (converging electric field) and an associated sheet of outflowing field-aligned current, which is manifested by the polar arc. The enhanced cusp precipitation represents, in our view, the ionospheric footprint of the lobe reconnection process.

Key words. Magnetospheric physics (auroral phenomena; magnetopause, cusp, and boundary layers; plasma convection)

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