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Ann. Geophys., 25, 1617-1627, 2007
www.ann-geophys.net/25/1617/2007/
© European Geosciences Union 2007
Observations of significant flux closure by dual lobe reconnection
S. M. Imber1, S. E. Milan1, and B. Hubert2
1Department of Physics and Astronomy, University of Leicester, Leicester, UK
2Institut d'Atmospherique et de Geophysique, Université de Liège, Liège, Belgium
Abstract. We present an interval of dual lobe reconnection during which interplanetary
magnetic field lines are captured by the magnetosphere by reconnecting at
high latitudes in both the Northern and the Southern Hemispheres. This event
was identified using measurements of the ionospheric convection flow and
observations of the aurora using the SuperDARN radars and the IMAGE
spacecraft. A cusp spot, characteristic of northward IMF, is clearly visible
for a 30 min period enabling the ionospheric footprint of the Northern
Hemisphere merging gap to be accurately determined. During the interval a
strong burst of sunward flow across the dayside open/closed field line
boundary (OCB) is observed, which we interpret as the reconfiguration of the
magnetosphere following a burst of reconnection. Noon-midnight and dawn-dusk
keograms of the aurora show that the polar cap shrinks during the interval
indicating that a large amount of flux was closed by the reconnection. Using
the SuperDARN potential maps it is possible to calculate that the amount of
flux closed during the interval is 0.13 GWb which represents approximately
10% of the pre-existing polar cap. The number of ions captured by the
burst of dual lobe reconnection was calculated to be ~2.2×1031,
more than sufficient to populate a cold, dense plasma sheet. That a dense
plasma sheet was not subsequently observed is discussed in terms of
subsequent changes in the IMF.
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