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- Title
Oxygen Ion Dynamics in the Earth's Ring Current: Van Allen Probes Observations.
- Authors
Yue, Chao; Bortnik, Jacob; Li, Wen; Ma, Qianli; Wang, Chih‐Ping; Thorne, Richard M.; Lyons, Larry; Reeves, Geoffrey D.; Spence, Harlan E.; Gerrard, Andrew J.; Gkioulidou, Matina; Mitchell, Donald G.
- 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, while 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. Plain Language Summary: The behavior of the ionospheric O+ ions in the Earth's ring current should be carefully examined in order to advance our understanding of the role of ion composition in ring current dynamics. This problem has been extensively studied using past spacecraft missions. In this study, we revisit this problem based on almost 6 years of high‐quality data from the Van Allen Probes and have confirmed previous finding about the role of O+ ions to the ring current. For example, more O+ ions contribute to the ring current as sym‐H decreases, and O+ and total plasma pressures dramatically build up during storm time. Besides, our statistical results also provide evidence that without exception, ionospheric O+ ions make a significant contribution to the ring current during active time and their relative contribution to the ring current increases during the storm main phase and then decreases during the storm recovery phase compared to those of H+ ions, suggesting a faster buildup and decay of O+ pressure. In addition, the decrease of pressure anisotropy during the storm main phase is related to the pitch angle isotropization, which is probably caused by current sheet scattering or wave‐particle interaction. Key Points: We quantitatively examine how the total plasma pressure and pressure anisotropy changes with and without a substantial O+ ion populationO+ ions always make a nonnegligible contribution to the ring current when sym‐H < ‐60 nT with ℛ > 0.8The decrease of pressure anisotropy during storm main phase is related to pitch angle isotropization
- Subjects
RING currents; EARTH (Planet); OXYGEN; IONS; MAGNETOSPHERE; GEOMAGNETISM
- Publication
Journal of Geophysical Research. Space Physics, 2019, Vol 124, Issue 10, p7786
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1029/2019JA026801