Examining Coherency Scales, Substructure, and Propagation of Whistler Mode Chorus Elements With Magnetospheric Multiscale (MMS)

D. L Turner; A. N Jaynes; D. N Baker; D. P Hartley; J. H Lee; S. G Claudepierre; C. A Kletzing; J. F Fennell; O Santolik; J. B Blake; T Leonard; F. D Wilder; R. E Ergun; I. J Cohen; B. H Mauk; R. J Strangeway; H Breuillard; O Le Contel; Yu. V Khotyaintsev; R. B Torbert; R. C Allen; J. L Burch

doi:10.1002/2017JA024474

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Examining Coherency Scales, Substructure, and Propagation of Whistler Mode Chorus Elements With Magnetospheric Multiscale (MMS)

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Examining Coherency Scales, Substructure, and Propagation of Whistler Mode Chorus Elements With Magnetospheric Multiscale (MMS)

D. L Turner, A. N Jaynes, D. N Baker, D. P Hartley, J. H Lee, S. G Claudepierre, C. A Kletzing, J. F Fennell, O Santolik, J. B Blake, …

Journal of geophysical research. Space physics, Vol.122(11), pp.11,201-11,226

11/2017

DOI: 10.1002/2017JA024474

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Abstract

Whistler mode chorus waves are a naturally occurring electromagnetic emission observed in Earth's magnetosphere. Here, for the first time, data from NASA's Magnetospheric Multiscale (MMS) mission were used to analyze chorus waves in detail, including the calculation of chorus wave normal vectors, k. A case study was examined from a period of substorm activity around the time of a conjunction between the MMS constellation and NASA's Van Allen Probes mission on 07 April 2016. Chorus wave activity was simultaneously observed by all six spacecraft over a broad range of L shells (5.5 < L < 8.5), magnetic local time (06:00 < MLT < 09:00), and magnetic latitude (−32° < MLAT < −15°), implying a large chorus active region. Eight chorus elements and their substructure were analyzed in detail with MMS. These chorus elements were all lower band and rising tone emissions, right‐handed and nearly circularly polarized, and propagating away from the magnetic equator when they were observed at MMS (MLAT~−31°). Most of the elements had “hook”‐like signatures on their wave power spectra, characterized by enhanced wave power at flat or falling frequency following the peak, and all the elements exhibited complex and well‐organized substructure observed consistently at all four MMS spacecraft at separations up to 70 km (60 km perpendicular and 38 km parallel to the background magnetic field). The waveforms in field‐aligned coordinates also demonstrated that these waves were all phase coherent, allowing for the direct calculation of k. Error estimates on calculated k revealed that the plane wave approximation was valid for six of the eight elements and most of the subelements. The wave normal vectors were within 20–30° from the direction antiparallel to the background field for all elements and changed from subelement to subelement through at least two of the eight elements. The azimuthal angle of k in the perpendicular plane was oriented earthward and was oblique to that of the Poynting vector, which has implications for the validity of cold plasma theory. Key Points Cross‐correlation analysis was used to calculate the wave normal vector for eight rising tone lower band chorus elements and several subelements Substructure and wave phase were consistently coherent at all four MMS; plane wave approximation valid for six of eight elements up to 70 km scale Elements observed at L~8.2, MLT~06:53, MLAT~−31°; k was consistently oriented earthward and significantly oblique to B0 and S

chorus waves

inner magnetosphere

MMSMagnetospheric Multiscale

radiation belts

Van Allen Probes

Details

Title: Subtitle: Examining Coherency Scales, Substructure, and Propagation of Whistler Mode Chorus Elements With Magnetospheric Multiscale (MMS)
Creators: D. L Turner - The Aerospace Corporation
A. N Jaynes - University of Colorado Boulder
D. N Baker - University of Colorado Boulder
D. P Hartley - University of Iowa
J. H Lee - The Aerospace Corporation
S. G Claudepierre - The Aerospace Corporation
C. A Kletzing - University of Iowa
J. F Fennell - The Aerospace Corporation
O Santolik - Charles University
J. B Blake - The Aerospace Corporation
T Leonard - University of Colorado Boulder
F. D Wilder - University of Colorado Boulder
R. E Ergun - University of Colorado Boulder
I. J Cohen - Johns Hopkins University Applied Physics Laboratory
B. H Mauk - Johns Hopkins University Applied Physics Laboratory
R. J Strangeway - University of California, Los Angeles
H Breuillard - École Polytechnique
O Le Contel - École Polytechnique
Yu. V Khotyaintsev - Swedish Institute of Space Physics
R. B Torbert - University of New Hampshire
R. C Allen - Southwest Research Institute
J. L Burch - Southwest Research Institute
Resource Type: Journal article
Publication Details: Journal of geophysical research. Space physics, Vol.122(11), pp.11,201-11,226
DOI: 10.1002/2017JA024474
ISSN: 2169-9380
eISSN: 2169-9402
Number of pages: 26
Grant note: NASA (NNG04EB99C; NAS5‐01072)
Language: English
Date published: 11/2017
Academic Unit: Physics and Astronomy; University College Courses
Record Identifier: 9984199804602771

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