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Intense plasma waves at and near the solar wind termination shock


Plasma waves are a characteristic feature of shocks in plasmas, and are produced by non-thermal particle distributions that develop in the shock transition layer. The electric fields of these waves have a key role in dissipating energy in the shock and driving the particle distributions back towards thermal equilibrium1. Here we report the detection of intense plasma-wave electric fields at the solar wind termination shock. The observations were obtained from the plasma-wave instrument on the Voyager 2 spacecraft2. The first evidence of the approach to the shock was the detection of upstream electron plasma oscillations on 1 August 2007 at a heliocentric radial distance of 83.4 au (1 au is the Earth–Sun distance). These narrowband oscillations continued intermittently for about a month until, starting on 31 August 2007 and ending on 1 September 2007, a series of intense bursts of broadband electrostatic waves signalled a series of crossings of the termination shock at a heliocentric radial distance of 83.7 au. The spectrum of these waves is quantitatively similar to those observed at bow shocks upstream of Jupiter, Saturn, Uranus and Neptune.

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Figure 1: The first detection of electron plasma oscillations by Voyager 2 upstream of the termination shock.
Figure 2: Three bursts of broadband electrostatic noise of the type expected to occur at the termination shock.
Figure 3: A series of expanded timescale plots of the electric field intensities in the 10 to 311 Hz channels for event B.
Figure 4: Comparisons of the spectrum of the termination shock with spectra of planetary bow shocks.

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We wish to thank L. Burlaga and J. Richardson for discussions regarding the magnetometer and plasma data in advance of publication. The research at the University of Iowa was supported by NASA through the Jet Propulsion Laboratory.

Author Contributions D.A.G. is the principal investigator for the Voyager plasma-wave instruments and led the analysis. W.S.K. is the co-investigator and identified the wave signatures.

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Correspondence to D. A. Gurnett.

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Gurnett, D., Kurth, W. Intense plasma waves at and near the solar wind termination shock. Nature 454, 78–80 (2008).

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