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Observations of closed magnetic flux embedded in the lobe during periods of northward IMF
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  • Laura Jane Fryer,
  • Robert C Fear,
  • John C Coxon,
  • Imogen Gingell
Laura Jane Fryer
University of Southampton

Corresponding Author:[email protected]

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Robert C Fear
University of Southampton
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John C Coxon
University of Southampton
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Imogen Gingell
Imperial College London
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Abstract

The high latitude, lobe regions of the magnetosphere are often assumed to contain cool, low energy plasma populations. However, during periods of northward IMF, energetic plasma populations have occasionally been observed. We present three cases when Cluster observed uncharacteristically \say{hot} plasma populations in the lobe. For two of the three events, we present simultaneous observations of the plasma sheet observed by Double Star. The similarity between the plasma in the lobe and the plasma sheet suggests that the mechanism that produces plasma at high latitudes is likely to be tail reconnection, resulting in a trapped \say{wedge} of closed flux about the noon-midnight meridian. Complementary images from IMAGE and DMSP/SSUSI show that transpolar arcs, which form in each event in at least one hemisphere, directly intersect the footprint of the Cluster spacecraft in all three events. The intersection of the Cluster footprint with the transpolar arcs is synchronous with the observation of the energetic plasma populations in the lobe. This further supports the conclusion that it is likely this energetic plasma observed in the high latitude lobe regions of magnetosphere is on closed field lines.
Jun 2021Published in Journal of Geophysical Research: Space Physics volume 126 issue 6. 10.1029/2021JA029281