- Conference date: 25-30 Jun 1995
- Location: Dana Point, California (USA)
Measurements can be made of Very Long Baseline Interferometer (VLBI) phase scintillations due to plasma turbulence in the solar corona and solar wind. These measurements provide information on the spectrum and intensity of density fluctuations with scale sizes of a few hundred to several thousand kilometers. If we model the spatial power spectrum of the density fluctuations as where is the spatial wavenumber, these observations yield both α and the path-integrated value of The recently completed Very Long Baseline Array (VLBA) is capable of making such measurements over the heliocentric distance range from a few solar radii to 60 solar radii and beyond. This permits the determination, with the same technique and instrument, of the radial evolution of turbulent characteristics, as well as their dependence on solar wind transients, sector structure, etc. In this paper we present measurements of 16 sources observed at a wide range of solar elongations and at different times. These observations show that the coefficient depends on heliocentric distance as approximately The radio derived power spectral characteristics are in agreement with in situ measurements by the Helios spacecraft for regions of slow solar wind, but fast solar wind does not have large enough density fluctuations to account for the magnitude of the observed scintillations. The observed radial dependence is consistent with a Wentzel-Kramers-Brillouin (WKB)-type evolution of the turbulence with heliocentric distance.
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