Formation of the oxygen torus in the inner magnetosphere: Van Allen Probes observations
[1];
[7];
- Kyoto Univ. (Japan). Graduate School of Science, Data Analysis Center for Geomagnetism and Space Magnetism
- Kyoto Univ. (Japan). Graduate School of Science, Dept. of Geophysics
- Nagoya Univ. (Japan). Solar Terrestrial Environment Lab.
- Univ. of Iowa, Iowa City, IA (United States). Dept. of Physics and Astronomy
- Univ. of New Hampshire, Durham, NH (United States). Inst. for Earth, Oceans and Space
- NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States). Solar System Exploration Division
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Space Sciences and Applications Group
- The Inst. of Statistical Mathematics, Research Organization of Information and Systems, Tokyo (Japan)
Abstract We study the formation process of an oxygen torus during the 12–15 November 2012 magnetic storm, using the magnetic field and plasma wave data obtained by Van Allen Probes. We estimate the local plasma mass density ( ρ L ) and the local electron number density ( n e L ) from the resonant frequencies of standing Alfvén waves and the upper hybrid resonance band. The average ion mass ( M ) can be calculated by M ∼ ρ L / n e L under the assumption of quasi‐neutrality of plasma. During the storm recovery phase, both Probe A and Probe B observe the oxygen torus at L = 3.0–4.0 and L = 3.7–4.5, respectively, on the morning side. The oxygen torus has M = 4.5–8 amu and extends around the plasmapause that is identified at L ∼3.2–3.9. We find that during the initial phase, M is 4–7 amu throughout the plasma trough and remains at ∼1 amu in the plasmasphere, implying that ionospheric O + ions are supplied into the inner magnetosphere already in the initial phase of the magnetic storm. Numerical calculation under a decrease of the convection electric field reveals that some of thermal O + ions distributed throughout the plasma trough are trapped within the expanded plasmasphere, whereas some of them drift around the plasmapause on the dawnside. This creates the oxygen torus spreading near the plasmapause, which is consistent with the Van Allen Probes observations. We conclude that the oxygen torus identified in this study favors the formation scenario of supplying O + in the inner magnetosphere during the initial phase and subsequent drift during the recovery phase.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- National Aeronautics and Space Administration (NASA); Ministry of Education, Culture, Sports, Science and Technology (MEXT); USDOE
- Grant/Contract Number:
- AC52-06NA25396; 25287127; 921648; NAS5-01072; 967399
- OSTI ID:
- 1329553
- Alternate ID(s):
- OSTI ID: 1402177
- Report Number(s):
- LA-UR-15-20090
- Journal Information:
- Journal of Geophysical Research. Space Physics, Vol. 120, Issue 2; ISSN 2169-9380
- Publisher:
- American Geophysical UnionCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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