Observations of discrete harmonics emerging from equatorial noise

Michael A. Balikhin, Yuri Y. Shprits (), Simon N. Walker, Lunjin Chen, Nicole Cornilleau-Wehrlin, Iannis Dandouras, Ondrej Santolik, Christopher Carr, Keith H. Yearby and Benjamin Weiss
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Michael A. Balikhin: University of Sheffield
Yuri Y. Shprits: UCLA
Simon N. Walker: University of Sheffield
Lunjin Chen: W.B. Hanson Center for Space Sciences, The University of Texas at Dallas
Nicole Cornilleau-Wehrlin: LPP, CNRS, École Polytechnique
Iannis Dandouras: CNRS, IRAP
Ondrej Santolik: Institute of Atmospheric Physics ASCR
Christopher Carr: Blackett Laboratory, Imperial College London, South Kensington Campus
Keith H. Yearby: University of Sheffield
Benjamin Weiss: MIT

Nature Communications, 2015, vol. 6, issue 1, 1-6

Abstract: 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.

Date: 2015
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DOI: 10.1038/ncomms8703

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