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Ann. Geophys., 22, 141-158, 2004
www.ann-geophys.net/22/141/2004/
© European Geosciences Union 2004
Transient plasma injections in the dayside magnetosphere: one-to-one correlated observations by Cluster and SuperDARN
A. Marchaudon1, J.-C. Cerisier1, J.-M. Bosqued2, M. W. Dunlop3,*, J. A. Wild4, P. M. E. Décréau5, M. Förster6, D. Fontaine7, and H. Laakso8
1Centre d’Etude des Environnements Terrestre et Planétaires, 4 avenue de Neptune, 94107 Saint-Maur-des-Fossés Cedex, France
2Centre d’Etude Spatiale des Rayonnements, CESR/CNRS, B.P. 4346, 31028 Toulouse Cedex 4, France
3Space and Atmospheric Physics, Blackett Laboratory, Imperial College, London SW7 2BZ, UK
4Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK
5LPCE and Université d’Orléans, 45071 Orléans, France
6Max Planck-Institute für Extraterrestrische Physik, 85741 Garching, Germany
7Centre d’Etude des Environnements Terrestre et Planétaires, 10-12 avenue de l’Europe, 78140 Vélizy, France
8Space Science Division, ESTEC, Noordwijk, The Netherlands
*now at: RAL, Rutherford-Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, UK
Abstract. Conjunctions in the cusp between the four Cluster spacecraft and SuperDARN
ground-based radars offer unique opportunities to compare the signatures of transient plasma
injections simultaneously in the high-altitude dayside magnetosphere and in the ionosphere.
We report here on such observations on 17 March 2001, when the IMF initially northward
and duskward, turns southward and dawnward for a short period. The changes in the
convection direction at Cluster are well correlated with the interplanetary magnetic field
(IMF) By variations. Moreover, the changes in the ionosphere follow those in the
magnetosphere, with a 2–3min delay. When mapped into the ionosphere, the convection
velocity at Cluster is about 1.5 times larger than measured by SuperDARN.
In the high-altitude cusp, field and particle observations by Cluster display the
characteristic signatures of plasma injections into the magnetosphere suggestive of Flux
Transfer Events (FTEs). Simultaneous impulsive and localized convection plasma flows are
observed in the ionospheric cusp by the HF radars. A clear one-to-one correlation is observed
for three successive injections, with a 2–3min delay between the magnetospheric and
ionospheric observations. For each event, the drift velocity of reconnected flux tubes (phase
velocity) has been compared in the magnetosphere and in the ionosphere. The drift velocity
measured at Cluster is of the order of 400–600ms–1 when mapped into the ionosphere, in
qualitative agreement with SuperDARN observations. Finally, the reconnected flux tubes
are elongated in the north-south direction, with an east-west
dimension of 30–60km in the ionosphere from mapped Cluster observations, which is
consistent with SuperDARN observations, although slightly smaller.
Key words. Ionosphere (plasma convection) – Magnetospheric
physics (magnetopause, cusp, and boundary layers;
magnetosphere-ionosphere interactions)
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