A joint cluster and ground-based instrument study of two magnetospheric substorm events on 1st september 2002

Draper, N. C. and Lester, M. and Wild, J. A. and Milan, S. E. and Provan, G. and Grocott, A. and Cowley, S. W. H. and Bogdanova, Y. V. and Dewhirst, J. P. and Fazakerley, A. N. and Davies, J. A. and Bosqued, J. M. (2004) A joint cluster and ground-based instrument study of two magnetospheric substorm events on 1st september 2002. Annales Geophysicae, 22 (12). pp. 4217-4228. ISSN 0992-7689

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We present a coordinated ground- and space- based multi-instrument study of two magnetospheric substorm events that occurred on 1 September 2002, during the interval from 18:00 UT to 24:00 UT. Data from the Cluster and Polar spacecraft are considered in combination with ground-based magnetometer and HF radar data. During the first substorm event the Cluster spacecraft, which were in the Northern Hemisphere lobe, are to the west of the main region affected by the expansion phase. Nevertheless, substorm signatures are seen by Cluster at 18:25 UT (just after the expansion phase onset as seen on the ground at 18:23 UT), despite the ∼5 RE distance of the spacecraft from the plasma sheet. The Cluster spacecraft then encounter an earthward-moving diamagnetic cavity at 19:10 UT, having just entered the plasma sheet boundary layer. The second substorm expansion phase is preceded by pseudobreakups at 22:40 and 22:56 UT, at which time thinning of the near-Earth, L=6.6, plasma sheet occurs. The expansion phase onset at 23:05 UT is seen simultaneously in the ground magnetic field, in the magnetotail and at Polar’s near-Earth position. The response in the ionospheric flows occurs one minute later. The second substorm better fits the near-Earth neutral line model for substorm onset than the cross-field current instability model.

Item Type:
Journal Article
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Annales Geophysicae
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© European Geosciences Union 2004
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21 Apr 2008 10:49
Last Modified:
01 May 2022 00:16