Oxygen ion dynamics in the Earth's ring current: Van Allen probes observations
Date
2019-09-01
Authors
Yue, Chao
Bortnik, Jacob
Li, Wen
Ma, Qianli
Wang, Chih-Ping
Thorne, Richard M.
Lyons, Larry
Reeves, Geoffrey D.
Spense, Harlan E.
Gerrard, Andrew J.
Version
Accepted manuscript
OA Version
Citation
Chao Yue, Jacob Bortnik, Wen Li, Qianli Ma, Chih-Ping Wang, Richard Thorne, Larry Lyons, Geoffrey Reeves, Harlan Spense, Andrew Gerrard, Matina Gkioulidou, Donald Mitchell. 2019. "Oxygen Ion Dynamics in the Earth's Ring Current: Van Allen Probes Observations." Journal of Geophysical Research: Space Physics, Volume 124, Issue 10, pp. 7786-7798 https://doi.org/10.1029/2019JA026801
Abstract
Oxygen (O+) enhancements in the inner magnetosphere are often observed during geomagnetically active times, such as geomagnetic storms. In this study, we quantitatively examine the difference in ring current dynamics with and without a substantial O+ ion population based on almost 6 years of Van Allen Probes observations. Our results have not only confirmed previous finding of the role of O+ ions to the ring current but also found that abundant O+ ions are always present during large storms when sym-H < -60 nT without exception, whilst having the pressure ratio (𝓡) between O+ and proton (H+) larger than 0.8 and occasionally even larger than 1 when L < 3. Simultaneously, the pressure anisotropy decreases with decreasing sym-H and increasing L shell. The pressure anisotropy decrease during the storm main phase is likely related to the pitch angle isotropization processes. In addition, we find that 𝓡 increases during the storm main phase and then decreases during the storm recovery phase, suggesting faster buildup and decay of O+ pressure compared to H+ ions, which are probably associated with some species dependent source and/or energization as well as loss processes in the inner magnetosphere.