Storm time impulsive enhancements of energetic oxygen due to adiabatic acceleration of preexisting warm oxygen in the inner magnetosphere

Author
Keywords
Abstract
We examine enhancements of energetic (>50 keV) oxygen ions observed by the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) instrument on board the Van Allen Probes spacecraft in the inner magnetosphere (L ~ 6) at 22\textendash23 h magnetic local time (MLT) during an injection event of the 6 June 2013 storm. Simultaneous observations by two Van Allen Probes spacecraft located close together (~0.5 RE) indicate that particle injections occurred in the premidnight sector (< ~24 h MLT). We also examine the evolution of the proton and oxygen energy spectra at L ~ 6 during the injection event. The spectral slope did not significantly change during the storm. The oxygen phase space density (PSD) was shifted toward higher PSD in a wide range of the first adiabatic invariant. The spectral evolution manifests the characteristics of adiabatic acceleration and density increase of oxygen ions. Warm (0.1\textendash10 keV) oxygen measured by the Helium, Oxygen, Proton, and Electron (HOPE) instrument was enhanced prior to the storm mostly in magnetic field-aligned directions. The most reasonable scenario of this event is that warm oxygen ions that preexisted in the inner magnetosphere were picked up and adiabatically transported and accelerated by spatially localized, temporarily impulsive electric fields.
Year of Publication
2016
Journal
Journal of Geophysical Research: Space Physics
Volume
121
Number of Pages
7739-7752
Date Published
08/2016
URL
http://doi.wiley.com/10.1002/2016JA022384
DOI
10.1002/2016JA022384