O+ ion conic and plasma sheet dynamics observed by Van Allen Probe satellites during the 1 June 2013 magnetic storm. Issue 5 (7th May 2016)

• Record Type: Journal Article
• Authors: Burke, W. J.; Erickson, P. J.; Yang, J.; Foster, J.; Wygant, J.; Reeves, G.; Kletzing, C.
• Is Part Of: Journal of geophysical research. Volume 121:Issue 5(2016:May)
• Page Start: 4072
• Page End: 4091
• Publication Date: 2016-05-07
• Subjects: oxygen ion conics -- plasma sheet dynamics; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2015JA021795
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: The Van Allen Probe satellites were near apogee in the late evening local time sector during the 1 June 2013 magnetic storm's main phase. About an hour after crossing the ring current's "nose structure" into the plasma sheet, the satellites encountered a quasiperiodic sequence of 0.08–3 keV O + ions. Pitch angle distributions of this population consistently peaked nearly antiparallel to the local magnetic field. We interpret this population as O + conics originating in the northern ionosphere. Sequences began as fairly steady state conic fluxes with energies in the ~ 80 to 100 eV range. Over about a half hour buildup phase, O + energies peaked near 1 keV. During subsequent release phases lasting ~ 20 min, O + energies returned to low‐energy starting points. We argue these observations reflect repeated formations and dissolutions of downward, magnetically aligned electric fields ( ε || ) layers trapping O + conics between mirror points within heating layers below and electrostatic barriers above. Nearly identical variations were observed at the locations of both satellites during 9 of these 13 conic cycles. Phase differences between cycles were observed at both spacecraft during the remaining events. Most "buildup" to "release" phase transitions coincided with AL index minima. However, in situ magnetometer measurements indicate only weak dipolarizations of tail‐like magnetic fields. The lack of field‐aligned reflected O + and tail‐like magnetic fields suggest that both ionospheres may be active. However, Southern Hemisphere origin conics cannot be observed since they would be isotropized and accelerated during neutral sheet crossings. Key Points: Inner magnetosphere storm time O + ions are observed in situ at 100 s to 1000 s of eV energy Energetic ions may be provided by O + conics trapped between heating and electrostatic layers Energetic O + ions are supplied by only one hemisphere, implying neutral sheet isotropization