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Ann. Geophys., 26, 1545-1557, 2008
www.ann-geophys.net/26/1545/2008/
© European Geosciences Union 2008
Simultaneous tracking of reconnected flux tubes: Cluster and conjugate SuperDARN observations on 1 April 2004
Q.-H. Zhang1,2, R. Y. Liu2, M. W. Dunlop3, J. Y. Huang1, H. Q. Hu2, M. Lester4, Y. H. Liu2, Z. J. Hu2, Q. Q. Shi5, and M. G. G. T. Taylor6
1School of Science, Xidian University, Xi'an, China
2Polar Research Institute of China, Shanghai, China
3Rutherford-Appleton Laboratory, Chilton, Didcot, UK
4Department of physics and Astronomy, University of Leicester, Leicester, UK
5Center for Space Science and Applied Research (CSSAR), Chinese Academy of Sciences, Beijing, China
6Research and Scientific Support Department, ESA/ESTEC/SCI-SO Keplerlaan 1,2201AZ Noordwijk ZH, The Netherlands
Abstract. While the Cluster spacecraft were located near the high-latitude
magnetopause, between 11:30–13:00 UT on 1 April 2004, a series of medium to
large scale (40 nT, 0.6–1.2 Re) FTEs were observed. During this pass,
simultaneous and conjugated SuperDARN measurements are available that show a
global flow pattern which is consistent with the expected (mapped)
north-west motion of (predominantly sub-solar) reconnected, magnetic flux at
the magnetopause. We focus on analysing the local response of three FTEs,
tracking their magnetopause motion via the four-spacecraft measurements
together with their corresponding ground mapped motions. For two of these
FTEs, where the tracking is strongly coordinated with the ionospheric flow
at each footprint of the implied flux tubes in the Northern Hemisphere,
conditions corresponded to stable, increasing (>100°) clock angle,
while the third event, where the correspondence is less strong, coincided
with low (<100°) clock angle. Flux tube motion, both measured and
modeled from the inferred X-line, qualitatively matches the clear velocity
enhancements in ionospheric convections with northward and westward flow at
each location in the Northern Hemisphere, measured simultaneously by
SuperDARN, and also roughly matches the observed, south-eastward ionospheric
flow in the Southern Hemisphere at the time of these events. The time
periods of these velocity enhancements infer that the evolution time of the
FTEs is about 4–6 min from its origin on magnetopause to its addition
to the polar cap. However, the ionospheric response time in the Southern
Hemisphere might be 2 min longer for the 12:31 UT FTE (and 6 min
longer for the 12:51 UT FTE) than the response time in the Northern
Hemisphere.
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