6:15 PM - 7:30 PM
[PEM08-P01] Van Allen Probes observations of dipolarization and ion acceleration in the inner magnetosphere
We study magnetic field dipolarization and associated ion acceleration in the deep inner magnetosphere, using magnetic field and ion flux data obtained by the Van Allen Probes. First, from the magnetic field data recorded on the nightside (1800-0600 MLT) we selected candidate events in which the magnetic field in the component antiparallel to the dipole axis (i.e., H component in VDH coordinates) increases by more than 20 nT in 5 minutes. Second, the candidate events were scanned visually to confirm if they are accompanied by magnetic fluctuations. Finally, the geomagnetic AL, ASY, and Wp indices were examined to ensure that substorm activity was registered around the candidates events. These procedures yield 96 dipolarization events from 1 October 2012 to 31 October 2013. We find that dipolarization mostly occurs at L=4.5-6.5 before midnight (2100-0000 MLT). Some events are accompanied by O+ flux enhancements in the energy range of 1-10 keV, which is consistent with the AMPTE/CCE CHEM observation reported by Nosé et al. . We will discuss possible mechanisms of the selective acceleration of O+ ions in the inner magnetosphere during dipolarization.