O <sup>+</sup> Ion Conic and Plasma Sheet Dynamics Observed by Van Allen Probe Satellites during the 1 June 2013 Magnetic Storm

The Van Allen Probe satellites were near apogee in the late evening local time sector during the 1 June 2013 magnetic storm\textquoterights main phase. About an hour after crossing the ring current\textquoterights \textquotedblleftnose structure\textquotedblright into the plasma sheet, the satellites encountered a quasi-periodic sequence of 0.08 - 3 keV O+ ions. Pitch angle distributions of this population consistently peaked nearly anti-parallel 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 build-up phase, O+ energies peaked near 1 keV. During subsequent release phases lasting ~ 20 minutes, 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 [Gorney et al., 1985]. 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 \textquotedblleftbuild-up\textquotedblright to \textquotedblleftrelease\textquotedblright 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.
Year of Publication
Journal of Geophysical Research: Space Physics
Date Published