WIND observations of coherent electrostatic waves in the solar wind

A. Mangeney, C. Salem, C. Lacombe, J. L. Bougeret, C. Perche, R. Manning, P. J. Kellogg, K. Goetz, S. J. Monson, J. M. Bosqued

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The time domain sampler (TDS) experiment on WIND measures electric and magnetic wave forms with a sampling rate which reaches 120 000 points per second. We analyse here observations made in the solar wind near the Lagrange point L1. In the range of frequencies above the proton plasma frequency fpi and smaller than or of the order of the electron plasma frequency fpe, TDS observed three kinds of electrostatic (e.s.) waves: coherent wave packets of Langmuir waves with frequencies f ≃ fpe, coherent wave packets with frequencies in the ion acoustic range fpi ≤ f ≤ fpe, and more or less isolated non-sinusoidal spikes lasting less than 1 ms. We confirm that the observed frequency of the low frequency (LF) ion acoustic wave packets is dominated by the Doppler effect: the wavelengths are short, 10 to 50 electron Debye lengths λD. The electric field in the isolated electrostatic structures (IES) and in the LF wave packets is more or less aligned with the solar wind magnetic field. Across the IES, which have a spatial width of the order of ≃25λD, there is a small but finite electric potential drop, implying an average electric field generally directed away from the Sun. The IES wave forms, which have not been previously reported in the solar wind, are similar, although with a smaller amplitude, to the weak double layers observed in the auroral regions, and to the electrostatic solitary waves observed in other regions in the magnetosphere. We have also studied the solar wind conditions which favour the occurrence of the three kinds of waves: all these e.s. waves are observed more or less continuously in the whole solar wind (except in the densest regions where a parasite prevents the TDS observations). The type (wave packet or IES) of the observed LF waves is mainly determined by the proton temperature and by the direction of the magnetic field, which themselves depend on the latitude of WIND with respect to the heliospheric current sheet.

Original languageEnglish (US)
Pages (from-to)307-320
Number of pages14
JournalAnnales Geophysicae
Issue number3
StatePublished - Mar 1999

Bibliographical note

Funding Information:
Acknowledgements. The WAVES instrument on WIND was built by teams at the University of Minnesota, the University of Iowa and the Observatoire de Paris, Meudon, with support of NASA/ GSFC. M. L. Kaiser is the Deputy PI. Use of the key parameter MFI data and 3D-plasma data is courtesy of the teams of the Magnetic Field Investigation experiment (PI R.P. Lepping) and the Three Dimensional Plasma experiment (PI R.P. Lin), and of the ISTP CDHF team at NASA/GSFC. The French contribution is supported by the Centre National d'Etudes Spatiales and the Centre National de la Recherche Scientifique.


  • Interplanetary physics (plasma waves and turbulence; solar wind plasma)
  • Space plasma physics (electrostatic structures)


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