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The association of cusp-aligned arcs with plasma in the magnetotail implies a closed magnetosphere
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  • Stephen E. Milan,
  • Michaela K Mooney,
  • Gemma E. Bower,
  • Matthew G. G. T. Taylor,
  • Larry J. Paxton,
  • Iannis S Dandouras,
  • Andrew Fazakerley,
  • Christopher M. Carr,
  • Brian J. Anderson,
  • Sarah Kimberly Vines
Stephen E. Milan
University of Leicester

Corresponding Author:[email protected]

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Michaela K Mooney
University of Leicester
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Gemma E. Bower
University of Leicester
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Matthew G. G. T. Taylor
European Space Agency
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Larry J. Paxton
Johns Hopkins University
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Iannis S Dandouras
Institut de Recherche en Astrophysique et Planétologie, UPS-CNRS Toulouse, France
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Andrew Fazakerley
University College London, UK
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Christopher M. Carr
Imperial College
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Brian J. Anderson
John Hopkins Univ.
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Sarah Kimberly Vines
Johns Hopkins University Applied Physics Laboratory
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Abstract

We investigate a fifteen-day period in October 2011. Auroral observations by the SSUSI instrument onboard the DMSP F16, F17, and F18 spacecraft indicate that the polar regions were covered by weak cusp-aligned arc emissions whenever the IMF clock angle was small, |θ|<45°, which amounted to 30% of the time. Simultaneous observations of ions and electrons in the tail by the Cluster C4 and Geotail spacecraft showed that during these intervals dense (1 cm-3) plasma was observed, even as far from the equatorial plane of the tail as |ZGSE| = 13 RE. The ions had a pitch angle distribution peaking parallel and antiparallel to the magnetic field and the electrons had pitch angles that peaked perpendicular to the field. We interpret the counter-streaming ions and double loss-cone electrons as evidence that the plasma was trapped on closed field lines, and acted as a source for the cusp-aligned arc emission across the polar regions. This suggests that the magnetosphere was almost entirely closed during these periods. We further argue that the closure occured as a consequence of dual-lobe reconnection at the dayside magnetopause. Our finding forces a significant re-evaluation of the magnetic topology of the magnetosphere during periods of northwards IMF.
18 Feb 2023Submitted to ESS Open Archive
20 Feb 2023Published in ESS Open Archive