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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 21, issue 2
Ann. Geophys., 21, 539–558, 2003
https://doi.org/10.5194/angeo-21-539-2003
© Author(s) 2003. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 21, 539–558, 2003
https://doi.org/10.5194/angeo-21-539-2003
© Author(s) 2003. This work is distributed under
the Creative Commons Attribution 3.0 License.

  28 Feb 2003

28 Feb 2003

Multi-site observations of the association between aurora and plasma convection in the cusp/polar cap during a southeastward(By ~ |Bz|) IMF orientation

P. E. Sandholt1, J. Moen1, C. J. Farrugia2, S. W. H. Cowley3, M. Lester3, S. E. Milan3, C. Valladares4, W. F. Denig5, and S. Eriksson6 P. E. Sandholt et al.
  • 1Department of Physics, University of Oslo, Oslo, Norway
  • 2Space Science Center, University of New Hampshire, Durham, UK
  • 3Department of Physics and Astronomy, University of Leicester, UK
  • 4Institute for Scientific Research, Boston College, Newton Center, Mass., USA
  • 5Space Vehicles Directorate, Air Force Research Laboratory, Hanscom AFB, Mass., USA
  • 6Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, USA

Abstract. In a case study we demonstrate the spatiotemporal structure of aurora and plasma convection in the cusp/polar cap when the interplanetary magnetic field (IMF) Bz < 0 and By ~ | Bz | (clock angle in GSM Y - Z plane: ~ 135°). This IMF orientation elicited a response different from that corresponding to strongly northward and southward IMF. Our study of this "intermediate state" is based on a combination of ground observations of optical auroral emissions and ionospheric plasma convection. Utilizing all-sky cameras at NyAlesund, Svalbard and Heiss Island (Russian arctic), we are able to monitor the high-latitude auroral activity within the ~10:00–15:00 MLT sector. Information on plasma convection is obtained from the SuperDARN radars, with emphasis placed on line of sight observations from the radar situated in Hankasalmi, Finland (Cutlass). A central feature of the auroral observations in the cusp/polar cap region is a ~ 30-min long sequence of four brightening events, some of which consists of latitudinally and longitudinally separated forms, which are found to be associated with pulsed ionospheric flows in merging and lobe convection cells. The auroral/convection events may be separated into different forms/cells and phases, reflecting a spatiotem-poral evolution of the reconnection process on the dayside magnetopause. The initial phase consists of a brightening in the postnoon sector (~ 12:00–14:00 MLT) at ~ 73° MLAT, accompanied by a pulse of enhanced westward convection in the postnoon merging cell. Thereafter, the event evolution comprises two phenomena which occur almost simultaneously: (1) westward expansion of the auroral brightening (equatorward boundary intensification) across noon, into the ~ 10:00–12:00 MLT sector, where the plasma convection subsequently turns almost due north, in the convection throat, and where classical poleward moving auroral forms (PMAFs) are observed; and (2) auroral brightening at slightly higher latitudes (~ 75° MLAT) in the postnoon lobe cell, with expansion towards noon, giving rise to a clear cusp bifurcation. The fading phase of PMAFs is accompanied by a "patch" of enhanced (~ 1 km/s) poleward-directed merging cell convection at high latitudes (75–82° MLAT), e.g. more than 500 km poleward of the cusp equatorward boundary. The major aurora/convection events are recurring at ~ 5–10 min intervals.

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

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