Articles | Volume 19, issue 10/12
Ann. Geophys., 19, 1589–1612, 2001

Special issue: CLUSTER

Ann. Geophys., 19, 1589–1612, 2001

  30 Sep 2001

30 Sep 2001

Coordinated Cluster, ground-based instrumentation and low-altitude satellite observations of transient poleward-moving events in the ionosphere and in the tail lobe

M. Lockwood2,1, H. Opgenoorth3, A. P. van Eyken4, A. Fazakerley5, J.-M. Bosqued6, W. Denig7, J. A. Wild8, C. Cully9,3, R. Greenwald10, G. Lu11, O. Amm12, H. Frey21, A. Strømme13, P. Prikryl14, M. A. Hapgood1, M. N. Wild1, R. Stamper1, M. Taylor5, I. McCrea1, K. Kauristie12, T. Pulkkinen12, F. Pitout3, A. Balogh15, M. Dunlop15, H. Rème6, R. Behlke3, T. Hansen13, G. Provan8, P. Eglitis3, S. K. Morley2, D. Alcaydé6, P.-L. Blelly6, J. Moen16,17, E. Donovan9, M. Engebretson18, M. Lester8, J. Watermann19, and M. F. Marcucci20 M. Lockwood et al.
  • 1Solar Terrestrial Physics Division, Space Science and Technology Department, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, UK
  • 2Department of Physics and Astronomy, Southampton University, Southampton, UK
  • 3IRF, Swedish Institute of Space Physics, Uppsala Division, Sweden
  • 4EISCAT Scientific Association, Longyearbyen, Svalbard, Norway
  • 5Mullard Space Science Laboratory, Holmbury St. Mary, Surrey, UK
  • 6CESR, Centre d’Etude Spatiale des Rayonnements, Toulouse, France
  • 7Space Vehicles Directorate, Air Force Research Laboratory, Hanscom AFB, Massachusetts, USA
  • 8Department of Physics and Astronomy, Leicester University, Leicester, UK
  • 9University of Calgary, Calgary, Canada
  • 10Remote Sensing Group, Applied Physics Laboratory, John Hopkins University, Laurel, MD, USA
  • 11High Altitude Observatory, National Center for Atmospheric Research, Boulder, Colorado, USA
  • 12Finnish Meteorological Institute, Helsinki, Finland
  • 13University of Tromsø, Tromsø, Norway
  • 14Communications Research Centre, Ottawa, Ontario, Canada
  • 15Blackett Laboratory, Imperial College, London, UK
  • 16Department of Physics, University of Oslo, Blindern, Oslo, Norway
  • 17Also at Arctic Geophysics, University Courses on Svalbard, Longyearbyen, Norway
  • 18Department of Physics, Augsburg College, Minneapolis, MN, USA
  • 19Danish Meteorological Institute, Copenhagen, Denmark
  • 20Istituto di Fisica dello Spazio Interplanetario - CNR, Rome, Italyer, UK
  • 21University of California, Berkeley, California, USA

Abstract. During the interval between 8:00–9:30 on 14 January 2001, the four Cluster spacecraft were moving from the central magnetospheric lobe, through the dusk sector mantle, on their way towards intersecting the magnetopause near 15:00 MLT and 15:00 UT. Throughout this interval, the EISCAT Svalbard Radar (ESR) at Longyearbyen observed a series of poleward-moving transient events of enhanced F-region plasma concentration ("polar cap patches"), with a repetition period of the order of 10 min. Allowing for the estimated solar wind propagation delay of 75 ( ± 5) min, the interplanetary magnetic field (IMF) had a southward component during most of the interval. The magnetic footprint of the Cluster spacecraft, mapped to the ionosphere using the Tsyganenko T96 model (with input conditions prevailing during this event), was to the east of the ESR beams. Around 09:05 UT, the DMSP-F12 satellite flew over the ESR and showed a sawtooth cusp ion dispersion signature that also extended into the electrons on the equatorward edge of the cusp, revealing a pulsed magnetopause reconnection. The consequent enhanced ionospheric flow events were imaged by the SuperDARN HF backscatter radars. The average convection patterns (derived using the AMIE technique on data from the magnetometers, the EISCAT and SuperDARN radars, and the DMSP satellites) show that the associated poleward-moving events also convected over the predicted footprint of the Cluster spacecraft. Cluster observed enhancements in the fluxes of both electrons and ions. These events were found to be essentially identical at all four spacecraft, indicating that they had a much larger spatial scale than the satellite separation of the order of 600 km. Some of the events show a correspondence between the lowest energy magnetosheath electrons detected by the PEACE instrument on Cluster (10–20 eV) and the topside ionospheric enhancements seen by the ESR (at 400–700 km). We suggest that a potential barrier at the magnetopause, which prevents the lowest energy electrons from entering the magnetosphere, is reduced when and where the boundary-normal magnetic field is enhanced and that the observed polar cap patches are produced by the consequent enhanced precipitation of the lowest energy electrons, making them and the low energy electron precipitation fossil remnants of the magnetopause reconnection rate pulses.

Key words. Magnetospheric physics (polar cap phenomena; solar wind – magnetosphere interactions; magnetosphere – ionosphere interactions)

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