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

Abstract

Here 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 eL) 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 eL 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 expandedmore » 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:
ORCiD logo [1];  [2];  [3];  [4];  [4];  [4];  [5];  [6]; ORCiD logo [7];  [8];  [5];  [7]
  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:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
National Aeronautic 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

Citation Formats

Nose, Masahito, Oimatsu, S., Keika, K., Kletzing, C. A., Kurth, W. S., De Pascuale, S., Smith, C. W., MacDowall, R. J., Reeves, Geoffrey D., Nakano, S., Spence, H. E., and Larsen, Brian Arthur. Formation of the oxygen torus in the inner magnetosphere: Van Allen Probes observations. United States: N. p., 2015. Web. doi:10.1002/2014JA020593.
Nose, Masahito, Oimatsu, S., Keika, K., Kletzing, C. A., Kurth, W. S., De Pascuale, S., Smith, C. W., MacDowall, R. J., Reeves, Geoffrey D., Nakano, S., Spence, H. E., & Larsen, Brian Arthur. Formation of the oxygen torus in the inner magnetosphere: Van Allen Probes observations. United States. doi:10.1002/2014JA020593.
Nose, Masahito, Oimatsu, S., Keika, K., Kletzing, C. A., Kurth, W. S., De Pascuale, S., Smith, C. W., MacDowall, R. J., Reeves, Geoffrey D., Nakano, S., Spence, H. E., and Larsen, Brian Arthur. Thu . "Formation of the oxygen torus in the inner magnetosphere: Van Allen Probes observations". United States. doi:10.1002/2014JA020593. https://www.osti.gov/servlets/purl/1329553.
@article{osti_1329553,
title = {Formation of the oxygen torus in the inner magnetosphere: Van Allen Probes observations},
author = {Nose, Masahito and Oimatsu, S. and Keika, K. and Kletzing, C. A. and Kurth, W. S. and De Pascuale, S. and Smith, C. W. and MacDowall, R. J. and Reeves, Geoffrey D. and Nakano, S. and Spence, H. E. and Larsen, Brian Arthur},
abstractNote = {Here 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 (ρL) and the local electron number density (neL) from the resonant frequencies of standing Alfvén waves and the upper hybrid resonance band. The average ion mass (M) can be calculated by M ~ ρL/neL 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.},
doi = {10.1002/2014JA020593},
journal = {Journal of Geophysical Research. Space Physics},
number = 2,
volume = 120,
place = {United States},
year = {2015},
month = {2}
}

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