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Ann. Geophys., 19, 1589-1612, 2001
www.ann-geophys.net/19/1589/2001/
© European Geosciences Union 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. Lockwood1,2, H. Opgenoorth3, A. P. van Eyken4, A. Fazakerley5, J.-M. Bosqued6, W. Denig7, J. A. Wild8, C. Cully3,9, 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
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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