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Ann. Geophys., 23, 553-566, 2005
www.ann-geophys.net/23/553/2005/
© European Geosciences Union 2005
Localized fast flow disturbance observed in the plasma sheet and in the ionosphere
R. Nakamura1, O. Amm2, H. Laakso3, N. C. Draper4, M. Lester4, A. Grocott4, B. Klecker5, I. W. McCrea6, A. Balogh7, H. Rème8, and M. André9
1Inst. für Weltraumforschung der Österreichischen Akademie der Wissenschaften, A-8042, Graz, Austria
2Finnish Meteorological Institute, Space Research, FIN-00101 Helsinki, Finland
3Solar and Solar Terrestrial Missions Div., ESTEC, 2200 AG Noordwijk, The Netherlands
4Radio and Space Plasma Physics Group, Dept. of Phys. and Astron., Leicester LE17RH, UK
5Max-Planck Inst. für Extraterrestrische Physik, D-85748 Garching, Germany
6Space Science and Technology Dept., Rutherford Appleton Lab., Chilton, Didcot, Oxon OX11QX, UK
7Space and Atmospheric Phys. Group, Blackett Lab., Imperial College, London SW72BZ, UK
8Centre d’Etude Spatiale des Rayonnements, F-31028 Toulouse Cedex 4, France
9Swedish Institute of Space Physics, SE-75121 Uppsala, Sweden
Abstract. An isolated plasma sheet flow burst took place at 22:02 UT,
1 September 2002, when the Cluster footpoint was located within
the area covered by the Magnetometers-Ionospheric Radars-All-sky
Cameras Large Experiment (MIRACLE). The event was associated with
a clear but weak ionospheric disturbance and took place during a
steady southward IMF interval, about 1h preceding a major
substorm onset. Multipoint observations, both in space and from the
ground, allow us to discuss the temporal and spatial scale of the
disturbance both in the magnetosphere and ionosphere. Based on
measurements from four Cluster spacecraft it is inferred that
Cluster observed the dusk side part of a localized flow channel in
the plasma sheet with a flow shear at the front, suggesting a
field-aligned current out from the ionosphere. In the ionosphere
the equivalent current pattern and possible field-aligned current
location show a pattern similar to the auroral streamers
previously obtained during an active period, except for its spatial
scale and amplitude. It is inferred that the footpoint of Cluster
was located in the region of an upward field-aligned current,
consistent with the magnetospheric observations. The entire
disturbance in the ionosphere lasted about 10min, consistent with
the time scale of the current sheet disturbance in the
magnetosphere. The plasma sheet bulk flow, on the other hand, had
a time scale of about 2min, corresponding to the time scale of an
equatorward excursion of the enhanced electrojet. These
observations confirm that localized enhanced convection in the
magnetosphere and associated changes in the current sheet
structure produce a signature with consistent temporal and spatial
scale at the conjugate ionosphere.
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