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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 23, issue 11
Ann. Geophys., 23, 3513–3532, 2005
https://doi.org/10.5194/angeo-23-3513-2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 23, 3513–3532, 2005
https://doi.org/10.5194/angeo-23-3513-2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.

  21 Dec 2005

21 Dec 2005

Motion of the dayside polar cap boundary during substorm cycles: II. Generation of poleward-moving events and polar cap patches by pulses in the magnetopause reconnection rate

M. Lockwood1,*, J. A. Davies1, J. Moen2,**, A. P. van Eyken3, K. Oksavik2,***, I. W. McCrea1, and M. Lester4 M. Lockwood et al.
  • 1Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK
  • 2Department of Physics, University of Oslo, P.O. Box 1048 Blindern, N-0316 Oslo, Norway
  • 3EISCAT Headquarters, Kiruna, Sweden
  • 4Department of Physics and Astronomy, University of Leicester, Leicester, UK
  • *also at: Department of Physics and Astronomy, Southampton University, Southampton, Hampshire, UK
  • **also at: Arctic Geophysics, University Centre on Svalbard, N-9170 Longyearbyen, Norway
  • ***also at: Johns Hopkins University, Applied Physics Laboratory, Laurel, MD, USA, Norway

Abstract. Using data from the EISCAT (European Incoherent Scatter) VHF and CUTLASS (Co-operative UK Twin-Located Auroral Sounding System) HF radars, we study the formation of ionospheric polar cap patches and their relationship to the magnetopause reconnection pulses identified in the companion paper by Lockwood et al. (2005). It is shown that the poleward-moving, high-concentration plasma patches observed in the ionosphere by EISCAT on 23 November 1999, as reported by Davies et al. (2002), were often associated with corresponding reconnection rate pulses. However, not all such pulses generated a patch and only within a limited MLT range (11:00-12:00 MLT) did a patch result from a reconnection pulse. Three proposed mechanisms for the production of patches, and of the concentration minima that separate them, are analysed and evaluated: (1) concentration enhancement within the patches by cusp/cleft precipitation; (2) plasma depletion in the minima between the patches by fast plasma flows; and (3) intermittent injection of photoionisation-enhanced plasma into the polar cap. We devise a test to distinguish between the effects of these mechanisms. Some of the events repeat too frequently to apply the test. Others have sufficiently long repeat periods and mechanism (3) is shown to be the only explanation of three of the longer-lived patches seen on this day. However, effect (2) also appears to contribute to some events. We conclude that plasma concentration gradients on the edges of the larger patches arise mainly from local time variations in the subauroral plasma, via the mechanism proposed by Lockwood et al. (2000).

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