O+ Ion Conics and Plasma Sheet Dynamics during the 1 June 2013 Magnetic Storm
Tuesday, September 29, 2015
Philip John Erickson1, William J Burke2, Jun Yang3, John C Foster1, John R Wygant4, Reeves Geoffrey5 and Craig Kletzing6, (1)MIT Haystack Observatory, Westford, MA, United States, (2)Boston College, Institute for Scientific Research, Chestnut Hill, MA, United States, (3)University of Massachusetts, Lowell Center for Space, Science, and Technology, Lowell, MA, United States, (4)University of Minnesota Twin Cities, Minneapolis, MN, United States, (5)Los Alamos National Laboratory, Space and Atmospheric Sciences, Los Alamos, NM, United States, (6)University of Iowa, Iowa City, IA, United States
Abstract:
The Van Allen Probes (VAP) satellites were near apogee in the late evening 1 June 2013 magnetic storm’s main phase. About an hour after crossing the ring current’s “nose structure” into the plasma sheet, VAP satellites began to encounter a quasi-periodic sequence of 0.08 - 3 keV O+ ions. Because pitch angle distributions are peaked anti-parallel to the local magnetic field, we interpret this population as arising from O+ conics from the northern ionosphere. We argue these observations reflect repeated formations and dissolutions of downward, magnetically aligned electric field layers trapping O+ conics between mirror points within heating layers below and electrostatic barriers above [e.g. Gorney et al., 1985]. Nearly identical variations were observed at the locations of both VAP satellites during 9 of these 13 conic cycles. Phase difference between cycles were also observed by both spacecraft during the remaining events. Although most “build-up” to “release” phase transitions coincided with minima in the AL index, in situ magnetometer measurements indicate weak dipolarizations of tail-like magnetic fields. The lack of field-aligned reflected O+ and tail-like magnetic fields in the Van Allen Probes observations suggest that both ionospheres may be active in producing O+ ions, but both cannot be observed in the near-equatorial plane because ion conic populations are isotropized and accelerated during neutral sheet crossings.
