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

Journal Article · · Journal of Geophysical Research. Space Physics
DOI:https://doi.org/10.1002/2014JA020593· OSTI ID:1329553
 [1];  [2];  [3];  [4];  [4];  [4];  [5];  [6];  [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)
+ Show Author Affiliations
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.
Research Organization:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Organization:
Ministry of Education, Culture, Sports, Science and Technology (MEXT); NASA; USDOE
Grant/Contract Number:
AC52-06NA25396
OSTI ID:
1329553
Alternate ID(s):
OSTI ID: 1402177
Report Number(s):
LA-UR--15-20090
Journal Information:
Journal of Geophysical Research. Space Physics, Journal Name: Journal of Geophysical Research. Space Physics Journal Issue: 2 Vol. 120; ISSN 2169-9380
Publisher:
American Geophysical UnionCopyright Statement
Country of Publication:
United States
Language:
English

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Cited By (9)

Storm time occurrence and spatial distribution of Pc4 poloidal ULF waves in the inner magnetosphere: A Van Allen Probes statistical study journal June 2015
Global observations of magnetospheric high- m poloidal waves during the 22 June 2015 magnetic storm : Storm Time High- journal April 2017
Longitudinal Structure of Oxygen Torus in the Inner Magnetosphere: Simultaneous Observations by Arase and Van Allen Probe A journal October 2018
Roles of Flow Braking, Plasmaspheric Virtual Resonances, and Ionospheric Currents in Producing Ground Pi2 Pulsations journal November 2018
Low‐Energy (+ Ion Outflow Directly Into the Inner Magnetosphere: Van Allen Probes Observations journal January 2019
Simultaneous Trapping of Electromagnetic Ion Cyclotron and Magnetosonic Waves by Background Plasmas journal March 2019
MMS Measurements and Modeling of Peculiar Electromagnetic Ion Cyclotron Waves journal November 2019
L Versus Time Structures of Dayside Magnetic Pulsations Detected by the European Quasi‐Meridional Magnetometer Array journal August 2019
Propagation of EMIC Waves Inside the Plasmasphere: A Two‐Event Study journal November 2019

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Related Subjects

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