Year-end Sale % OFF 
Abstract
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.
Highlights
The coupling between the Interplanetary Magnetic Field (IMF) and the magnetosphere has been extensively studied over the last few decades, but there are still many unanswered questions with regard to how the magnetosphere responds to different IMF conditions, when the IMF is northward
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
In this study we look at two specific, contrasting theories, which describe mechanisms which could lead to the presence of “hot” plasma embedded in the lobes (Milan et al, 2005; Shi et al, 2013)
Summary
The coupling between the Interplanetary Magnetic Field (IMF) and the magnetosphere has been extensively studied over the last few decades, but there are still many unanswered questions with regard to how the magnetosphere responds to different IMF conditions, when the IMF is northward. Following on from this, Fear et al (2014) studied electron pitch angle distributions, which showed evidence of a double loss cone This finding, in conjunction with the similarity of the temperature and density to that of the plasma sheet, supported the theory that the origin of the plasma observed in the lobe was not likely to be from direct solar wind entry (which require an open topology), but can be explained well by tail reconnection and form due to the closure of magnetic field lines in the lobe. This study supports both the proposed model of TPA formation, and that the presence of energetic plasma in the lobe is a result of nightside tail reconnection The latter process forms a wedge of trapped closed field lines surrounded by the typical open lobe field lines (Fear et al, 2015; Milan et al, 2005)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
