Turbulence analysis of the Jovian upstream ‘wave’ phenomenon

Authors:
  • CSCharles W. Smith
    Charles W. Smith
  • MGMelvyn L. Goldstein
    Melvyn L. Goldstein
  • WMWilliam H. Matthaeus
    William H. Matthaeus
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Abstract
As Voyager 2 approached Jupiter's bow shock, large‐amplitude fluctuations were seen in both the magnetic field and plasma fluid velocity. These fluctuations generally coincided with the occurrence of long‐lived energetic particle events similar to the upstream waves often observed near the earth's bow shock. In this paper we present an analysis of the magnetic field and plasma observations using spectral methods. The characteristic spectral features related to the upstream waves are generally seen near 1 mHz. The measured correlation lengths of these fluctuations suggest that they are coherent over only a few wavelengths. Our analysis is consistent with the hypothesis that these fluctuations are driven by streaming ions, possibly protons. No evidence for the existence of whistler waves is found. We argue that some of the observed spectral features suggest that dynamical turbulent processes are occurring in the upstream wave region, including a possible observation of an inverse cascade of magnetic helicity to large spatial scales.

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