Journal cover Journal topic
Annales Geophysicae An interactive open-access journal of the European Geosciences Union
Journal topic

Journal metrics

Journal metrics

  • IF value: 1.490 IF 1.490
  • IF 5-year value: 1.445 IF 5-year
    1.445
  • CiteScore value: 2.9 CiteScore
    2.9
  • SNIP value: 0.789 SNIP 0.789
  • IPP value: 1.48 IPP 1.48
  • SJR value: 0.74 SJR 0.74
  • Scimago H <br class='hide-on-tablet hide-on-mobile'>index value: 88 Scimago H
    index 88
  • h5-index value: 21 h5-index 21
Volume 23, issue 11
Ann. Geophys., 23, 3495–3511, 2005
https://doi.org/10.5194/angeo-23-3495-2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 23, 3495–3511, 2005
https://doi.org/10.5194/angeo-23-3495-2005
© 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: I. Observations of pulses in the magnetopause reconnection rate

M. Lockwood1,*, J. Moen2,**, A. P. van Eyken3, J. A. Davies1, K. Oksavik2,***, and I. W. McCrea1 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
  • *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

Abstract. Using data from the EISCAT (European Incoherent Scatter) VHF radar and DMSP (Defense Meteorological Satellite Program) spacecraft passes, we study the motion of the dayside open-closed field line boundary during two substorm cycles. The satellite data show that the motions of ion and electron temperature boundaries in EISCAT data, as reported by Moen et al. (2004), are not localised around the radar; rather, they reflect motions of the open-closed field line boundary at all MLT throughout the dayside auroral ionosphere. The boundary is shown to erode equatorward when the IMF points southward, consistent with the effect of magnetopause reconnection. During the substorm expansion and recovery phases, the dayside boundary returns poleward, whether the IMF points northward or southward. However, the poleward retreat was much faster during the substorm for which the IMF had returned to northward than for the substorm for which the IMF remained southward - even though the former substorm is much the weaker of the two. These poleward retreats are consistent with the destruction of open flux at the tail current sheet. Application of a new analysis of the peak ion energies at the equatorward edge of the cleft/cusp/mantle dispersion seen by the DMSP satellites identifies the dayside reconnection merging gap to extend in MLT from about 9.5 to 15.5 h for most of the interval. Analysis of the boundary motion, and of the convection velocities seen near the boundary by EISCAT, allows calculation of the reconnection rate (mapped down to the ionosphere) from the flow component normal to the boundary in its own rest frame. This reconnection rate is not, in general, significantly different from zero before 06:45 UT (MLT<9.5 h) - indicating that the X line footprint expands over the EISCAT field-of-view to earlier MLT only occasionally and briefly. Between 06:45 UT and 12:45 UT (9.5<MLT<15.5 h) reconnection is continuously observed by EISCAT, confirming the (large) MLT extent of the reconnection footprint deduced from the DMSP passes. As well as direct control by the IMF on longer timescales, the derived reconnection rate variation shows considerable pulsing on timescales of 2-20 min during periods of steady southward IMF.

Publications Copernicus
Download
Citation