The relationship between the macroscopic state of electrons and the properties of chorus waves observed by the Van Allen Probes

Chao Yue; Xin An; Jacob Bortnik; Qianli Ma; Wen Li; Richard M Thorne; Geoffrey D Reeves; Matina Gkioulidou; Donald G Mitchell; Craig A Kletzing

doi:10.1002/2016GL070084

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The relationship between the macroscopic state of electrons and the properties of chorus waves observed by the Van Allen Probes

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The relationship between the macroscopic state of electrons and the properties of chorus waves observed by the Van Allen Probes

Chao Yue, Xin An, Jacob Bortnik, Qianli Ma, Wen Li, Richard M Thorne, Geoffrey D Reeves, Matina Gkioulidou, Donald G Mitchell and Craig A Kletzing

Geophysical research letters, Vol.43(15), pp.7804-7812

08/16/2016

DOI: 10.1002/2016GL070084

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Abstract

Plasma kinetic theory predicts that a sufficiently anisotropic electron distribution will excite whistler mode waves, which in turn relax the electron distribution in such a way as to create an upper bound on the relaxed electron anisotropy. Here using whistler mode chorus wave and plasma measurements by Van Allen Probes, we confirm that the electron distributions are well constrained by this instability to a marginally stable state in the whistler mode chorus waves generation region. Lower band chorus waves are organized by the electron β∥e into two distinct groups: (i) relatively large‐amplitude, quasi‐parallel waves with β∥e≳0.025 and (ii) relatively small‐amplitude, oblique waves with β∥e≲0.025. The upper band chorus waves also have enhanced amplitudes close to the instability threshold, with large‐amplitude waves being quasi‐parallel whereas small‐amplitude waves being oblique. These results provide important insight for studying the excitation of whistler mode chorus waves. Key Points The electron distributions are constrained to a marginally stable state by the whistler anisotropy instability Quasi‐parallel and oblique lower band chorus waves are separated by β∥e = 0.025 A correlation between the wave normal angle and wave amplitude is seen for both lower and upper band chorus waves

beta parallel

electron temperature anisotropy

marginally stable state

oblique waves

quasi‐parallel waves

whistler mode chorus waves

Details

Title: Subtitle: The relationship between the macroscopic state of electrons and the properties of chorus waves observed by the Van Allen Probes
Creators: Chao Yue - University Corporation for Atmospheric Research
Xin An - University of California, Los Angeles
Jacob Bortnik - University of California, Los Angeles
Qianli Ma - University of California, Los Angeles
Wen Li - University of California, Los Angeles
Richard M Thorne - University of California, Los Angeles
Geoffrey D Reeves - Los Alamos National Laboratory
Matina Gkioulidou - Johns Hopkins University Applied Physics Laboratory
Donald G Mitchell - Johns Hopkins University Applied Physics Laboratory
Craig A Kletzing - University of Iowa
Resource Type: Journal article
Publication Details: Geophysical research letters, Vol.43(15), pp.7804-7812
DOI: 10.1002/2016GL070084
ISSN: 0094-8276
eISSN: 1944-8007
Number of pages: 9
Grant note: NSF (AGS-1405054) NASA (NNX13AI61G; NNX15AF61G; NNX14AI18G; NAS5-01072) Department of Energy and the National Science Foundation (DE-SC0010578)
Language: English
Date published: 08/16/2016
Academic Unit: Physics and Astronomy
Record Identifier: 9984199932202771

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