Title: Formation of the oxygen torus in the inner magnetosphere: Van Allen Probes observations

Abstract

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 somemore » 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.« less

Authors:

Nose, Masahito  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-2789-3588"

Oimatsu, S. ^[2]; Keika, K. ^[3]; Kletzing, C. A. ^[4]; Kurth, W. S. ^[4]; De Pascuale, S. ^[4]; Smith, C. W. ^[5]; MacDowall, R. J. ^[6]; Reeves, Geoffrey D.  ^[7];

• Search DOE PAGES for author "Reeves, Geoffrey D."
• Search DOE PAGES for ORCID "0000-0002-7985-8098"

Nakano, S. ^[8]; Spence, H. E. ^[5]; Larsen, Brian Arthur ^[7]

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+ Show Author Affiliations

1. Kyoto Univ. (Japan). Graduate School of Science, Data Analysis Center for Geomagnetism and Space Magnetism
2. Kyoto Univ. (Japan). Graduate School of Science, Dept. of Geophysics
3. Nagoya Univ. (Japan). Solar Terrestrial Environment Lab.
4. Univ. of Iowa, Iowa City, IA (United States). Dept. of Physics and Astronomy
5. Univ. of New Hampshire, Durham, NH (United States). Inst. for Earth, Oceans and Space
6. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States). Solar System Exploration Division
7. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Space Sciences and Applications Group
8. The Inst. of Statistical Mathematics, Research Organization of Information and Systems, Tokyo (Japan)

Publication Date:

Thu Feb 19 00:00:00 EST 2015

Research Org.:

Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)

Sponsoring Org.:

National Aeronautics and Space Administration (NASA); Ministry of Education, Culture, Sports, Science and Technology (MEXT); USDOE

OSTI Identifier:

1329553

Alternate Identifier(s):

OSTI ID: 1402177

Report Number(s):

LA-UR-15-20090
Journal ID: ISSN 2169-9380

Grant/Contract Number:  

AC52-06NA25396; 25287127; 921648; NAS5-01072; 967399

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Geophysical Research. Space Physics

Additional Journal Information:

Journal Volume: 120; Journal Issue: 2; Journal ID: ISSN 2169-9380

Publisher:

American Geophysical Union

Country of Publication:

United States

Language:

English

Subject:

58 GEOSCIENCES; inner magnetosphere; oxygen torus; magnetic storm; plasmasphere; ring current; ULF waves