Bibliography
Notice:
|
Found 2 entries in the Bibliography.
Showing entries from 1 through 2
2016 |
We investigate magnetic field dipolarization in the inner magnetosphere and its associated ion flux variations, using the magnetic field and energetic ion flux data acquired by the Van Allen Probes. From a study of 74 events that appeared at L = 4.5\textendash6.6 between 1 October 2012 and 31 October 2013, we reveal the following characteristics of the dipolarization in the inner magnetosphere: (1) its timescale is approximately 5 min, (2) it is accompanied by strong magnetic fluctuations that have a dominant frequency close to the O+ gyrofrequency, (3) ion fluxes at 20\textendash50 keV are simultaneously enhanced with larger magnitudes for O+ than for H+, (4) after a few minutes of the dipolarization, the flux enhancement at 0.1\textendash5 keV appears with a clear energy-dispersion signature only for O+, and (5) the energy-dispersed O+ flux enhancement appears in directions parallel or anti-parallel to the magnetic field. From these characteristics, we discuss possible mechanisms that can provide selective acceleration to O+ ions at >20 keV. We conclude that O+ ions at L = 5.4\textendash6.6 undergo nonadiabatic local acceleration caused by oscillating electric field associated with the magnetic fluctuations and/or adiabatic convective transport from the plasma sheet to the inner magnetosphere by the impulsive electric field. At L = 4.5\textendash5.4, however, only the former acceleration is plausible. We also conclude that the field-aligned energy-dispersed O+ ions at 0.1\textendash5 keV originate from the ionosphere and are extracted nearly simultaneously to the onset of the dipolarization. e, M.; Keika, K.; Kletzing, C.; Spence, H.; Smith, C.; MacDowall, R.; Reeves, G.; Larsen, B.; Mitchell, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2016 YEAR: 2016   DOI: 10.1002/2016JA022549 Dipolarization; inner magnetosphere; ionospheric outflow; Magnetic Fluctuation; O+ Acceleration; substorm; Van Allen Probes |
Driving ionospheric outflows and magnetospheric O + energy density with Alfv\ en waves We show how dispersive Alfv\ en waves observed in the inner magnetosphere during geomagnetic storms can extract O+ ions from the topside ionosphere and accelerate these ions to energies exceeding 50 keV in the equatorial plane. This occurs through wave trapping, a variant of \textquotedblleftshock\textquotedblright surfing, and stochastic ion acceleration. These processes in combination with the mirror force drive field-aligned beams of outflowing ionospheric ions into the equatorial plane that evolve to provide energetic O+ distributions trapped near the equator. These waves also accelerate preexisting/injected ion populations on the same field lines. We show that the action of dispersive Alfv\ en waves over several minutes may drive order of magnitude increases in O+ ion pressure to make substantial contributions to magnetospheric ion energy density. These wave accelerated ions will enhance the ring current and play a role in the storm time evolution of the magnetosphere. Chaston, C.; Bonnell, J.; Reeves, G.; Skoug, R.; Published by: Geophysical Research Letters Published on: 05/2016 YEAR: 2016   DOI: 10.1002/2016GL069008 Alfven waves; ion acceleration; Ionosphere; ionospheric outflow; ring current |
1