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Ann. Geophys., 22, 2181-2199, 2004
www.ann-geophys.net/22/2181/2004/
© European Geosciences Union 2004
Simultaneous observations of magnetopause flux transfer events and of their associated signatures at ionospheric altitudes
K. A. McWilliams1, G. J. Sofko1, T. K. Yeoman2, S. E. Milan2, D. G. Sibeck3,7, T. Nagai4, T. Mukai5, I. J. Coleman6, T. Hori7, and F. J. Rich8
1Institute of Space and Atmospheric Studies, University of Saskatchewan, Saskatoon, Canada
2Department of Physics and Astronomy, University of Leicester, Leicester, UK
3NASA/GSFC, Greenbelt, Maryland, USA
4Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo, Japan
5Institute of Space and Astronautical Science, Kanagawa, Japan
6British Antarctic Survey, Cambridge, UK
7Johns Hopkins University, Applied Physics Laboratory, Laurel, Maryland, USA
8AFRL/VSBXP, Hanscom AFB, Massachusetts, USA
Abstract. An extensive variety of instruments, including Geotail, DMSP F11, SuperDARN,
and IMP-8, were monitoring the dayside magnetosphere and ionosphere between
14:00 and 18:00 UT on 18 January 1999. The location of the instruments
provided an excellent opportunity to study in detail the direct coupling
between the solar wind, the magnetosphere, and the ionosphere. Flux transfer
events were observed by Geotail near the magnetopause in the dawn side
magnetosheath at about 4 magnetic local time during exclusively northward
interplanetary magnetic field conditions. Excellent coverage of the
entire dayside high-latitude ionosphere was achieved by the
Northern Hemisphere SuperDARN radars. On the large scale, temporally and spatially,
the dayside magnetosphere convection remained directly driven by the
interplanetary magnetic field, despite the highly variable interplanetary
magnetic field conditions, including long periods of northward field. The
SuperDARN radars in the dawn sector also measured small-scale temporally
varying convection velocities, which are indicative of flux transfer event activity, in the
vicinity of the magnetic footprint of Geotail. DMSP F11 in the
Southern Hemisphere measured typical cusp precipitation simultaneously with and
magnetically conjugate to a single flux transfer event signature detected by
Geotail. A study of the characteristics of the DMSP ion spectrogram revealed
that the source plasma from the reconnection site originated downstream of
the subsolar point. Detailed analyses of locally optimised coordinate systems
for individual flux transfer events at Geotail are consistent with a series
of flux tubes protruding from the magnetopause, and originating from a
high-latitude reconnection site in the Southern Hemisphere. This
high-latitude reconnection site agrees with plasma injected
away from the subsolar point. This is the first simultaneous and independent
determination from ionospheric and space-based data of the location of
magnetic reconnection.
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