title: Observations of discrete harmonics emerging from equatorial noise.
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.
authors.affiliation: Department of Automatic Control and Systems Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Balikhin
authors.affiliation: 1] Department of Earth Planetary and Space Sciences, UCLA, 595 Charles Young Drive East, Box 951567, Los Angeles, California 90095-1567, USA [2] Department of Earth Atmospheric and Planetary Sciences, MIT, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, USA.
authors.forename: Yuri Y
authors.initials: YY
authors.lastname: Shprits
authors.affiliation: Department of Automatic Control and Systems Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK.
authors.forename: Simon N
authors.initials: SN
authors.lastname: Walker
authors.affiliation: W.B. Hanson Center for Space Sciences, Department of Physics, The University of Texas at Dallas, 800 West Campbell Road, Richardson, Texas 75080-3021, USA.
authors.forename: Lunjin
authors.initials: L
authors.lastname: Chen
authors.affiliation: 1] LPP, CNRS, École Polytechnique, Palaiseau 91128, France [2] LESIA, Observatoire de Paris, Section de Meudon, 5, Place Jules Janssen, Meudon 92195, France.
authors.forename: Nicole
authors.initials: N
authors.lastname: Cornilleau-Wehrlin
authors.affiliation: 1] CNRS, IRAP, 9, Avenue du Colonel Roche, Toulouse BP 44346-31028, France [2] UPS-OMP, IRAP, 14, Avenue Edouard Belin, Toulouse 31400, France.
authors.forename: Iannis
authors.initials: I
authors.lastname: Dandouras
authors.affiliation: 1] Department of Space Physics, Institute of Atmospheric Physics ASCR, Bocni II/1401, 14131 Praha 4, Czech Republic [2] Faculty of Mathematics and Physics, Charles University in Prague, V Holesovickach 2, 18000 Praha 8, Czech Republic.
authors.forename: Ondrej
authors.initials: O
authors.lastname: Santolik
authors.affiliation: Blackett Laboratory, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.
authors.forename: Christopher
authors.initials: C
authors.lastname: Carr
authors.affiliation: Department of Automatic Control and Systems Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK.
authors.forename: Keith H
authors.initials: KH
authors.lastname: Yearby
authors.affiliation: Department of Earth Atmospheric and Planetary Sciences, MIT, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Weiss