Observations of Closed Magnetic Flux Embedded in the Lobes During Periods of Northward IMF

• Published in: Journal of geophysical research. Space physics 2021-06, Vol.126 (6), p.e2021JA029281-n/a
• Main Authors: Fryer, L. J., Fear, R. C., Coxon, J. C., Gingell, I. L.
• Format: Article
• Language: English
• Subjects: Auroral Ionosphere; Auroral Phenomena; Cluster 20th anniversary: results from the first 3D mission; Energetic Particles: Trapped; Ionosphere; Magnetospheric Configuration and Dynamics; Magnetospheric Physics; Magnetotail; Polar CaP Phenomena
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2021JA029281

The high latitude, lobe regions of the magnetosphere are often assumed to contain cool, low energy plasma populations. However, during periods of northward Interplanetary Magnetic Field, energetic plasma populations have occasionally been observed. We present three cases when Cluster observed uncharacteristically “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 “wedge” of closed flux about the noon‐midnight meridian. Complementary images from Imager for Magnetopause to Aurora Global Exploration and DMSP/Special Sensor Ultraviolet Spectrographic Imager 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. Key Points Cluster observations of hot plasma in the lobe are directly comparable to simultaneous observations of the plasma sheet by Double Star Plasma observations suggest that tail reconnection is the cause for the presence of energetic plasma in the high latitude magnetosphere Imaging spacecraft support previous findings which show an association between transpolar arcs and energetic plasma observed in the lobe