Observations of discrete harmonics emerging from equatorial noise
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Weiss_Observations of discrete.pdf
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Author(s)
Balikhin, Michael A.
Walker, Simon N.
Chen, Lunjin
Cornilleau-Wehrlin, Nicole
Dandouras, Iannis
Santolik, Ondrej
Carr, Christopher E.
Yearby, Keith H.
Shprits, Yuri
Weiss, Benjamin P.
Date Issued
July 2015
Journal
Nature Communications
Publisher
Nature Publishing Group
Citation
Balikhin, Michael A., Yuri Y. Shprits, Simon N. Walker, Lunjin Chen, Nicole Cornilleau-Wehrlin, Iannis Dandouras, Ondrej Santolik, Christopher Carr, Keith H. Yearby, and Benjamin Weiss. “Observations of Discrete Harmonics Emerging from Equatorial Noise.” Nature Communications 6 (July 14, 2015): 7703. © 2015 Macmillan Publishers Limited
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Final published version
Abstract
A number of modes of oscillations of particles and fields can exist in space plasmas. Since the early 1970s, space missions have observed noise-like plasma waves near the geomagnetic equator known as ‘equatorial noise’. Several theories were suggested, but clear observational evidence supported by realistic modelling has not been provided. Here we report on observations by the Cluster mission that clearly show the highly structured and periodic pattern of these waves. Very narrow-banded emissions at frequencies corresponding to exact multiples of the proton gyrofrequency (frequency of gyration around the field line) from the 17th up to the 30th harmonic are observed, indicating that these waves are generated by the proton distributions. Simultaneously with these coherent periodic structures in waves, the Cluster spacecraft observes ‘ring’ distributions of protons in velocity space that provide the free energy for the waves. Calculated wave growth based on ion distributions shows a very similar pattern to the observations.
MIT Department
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
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DOI of Published Version
http://dx.doi.org/10.1038/ncomms8703
