Title: Test of Ion Cyclotron Resonance Instability Using Proton Distributions Obtained From Van Allen Probe-A Observations

Abstract

Anisotropic velocity distributions of protons have long been considered as free energy sources for exciting electromagnetic ion cyclotron (EMIC) waves in the Earth's magnetosphere. Here we rigorously calculated the proton anisotropy parameter using proton data obtained from Van Allen Probe–A observations. The calculations are performed for times during EMIC wave events (distinguishing the times immediately after and before EMIC wave onsets) and for times exhibiting no EMIC waves. We find that the anisotropy values are often larger immediately after EMIC wave onsets than the times just before EMIC wave onsets and the non–EMIC wave times. The increase in anisotropy immediately after the EMIC wave onsets is rather small but discernible, such that the average increase is by ~15% relative to the anisotropy values during the non–EMIC wave times and ~8% compared to those just before the EMIC wave onsets. Based on the calculated anisotropy values, we test the criterion for ion cyclotron instability suggested by Kennel and Petschek by applying it to the EMIC wave events. We find that despite the weak increase in anisotropy, the majority of the EMIC wave events satisfy the instability criterion. We suggest that the proton distributions often remain close to the marginal state tomore » ion cyclotron instability, and consequently, the proton anisotropy values should often be observed near threshold values for ion cyclotron instability. In conclusion, we demonstrate the usefulness and limitation of the instability criteria expressed in the form of an inverse relation between the anisotropy and plasma beta.« less

Authors:

Noh, Sung -Jun  ^[1];

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Lee, Dae -Young  ^[1];

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Choi, Cheong -Rim ^[1]; Kim, Hyomin  ^[2];

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Skoug, Ruth M.  ^[3]

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+ Show Author Affiliations

1. Chungbuk National Univ., Cheongju (South Korea)
2. New Jersey Institute of Technology, Newark, NJ (United States)
3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Publication Date:

2018-08-06

Research Org.:

Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Sponsoring Org.:

National Aeronautic and Space Administration (NASA); USDOE

OSTI Identifier:

1467214

Report Number(s):

[LA-UR-18-21529]
[Journal ID: ISSN 2169-9380]

Grant/Contract Number:  

[AC52-06NA25396]

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Geophysical Research. Space Physics

Additional Journal Information:

[ Journal Volume: 123; Journal Issue: 8]; Journal ID: ISSN 2169-9380

Publisher:

American Geophysical Union

Country of Publication:

United States

Language:

English

Subject:

79 ASTRONOMY AND ASTROPHYSICS; Heliospheric and Magnetospheric Physics