Properties of solar wind turbulence deduced by radio astronomical measurements
Abstract
A simple ray analysis is used to derive expressions for the angular spread and spectral broadening of coherent radio signals on traversing the turbulent interplanetary medium, when the anisotropy and radial gradient of the turbulence and the large-scale motions of the medium (solar wind) are important. The resulting expressions are used to interpret observations, reported in the literature, of the angular broadening of natural radio sources and of the spectral broadening of Mariner 4 during superior conjunction. In the region 10-100 solar radii our results are consistent with a coronal electron concentration behaving as r-2 and a statistical correlation length which during solar minimum does not vary with r but which tends to increase linearly with r near solar maximum, indicating that the interplanetary plasma tends to develop a radial filamentary structure during solar maximum; we find no necessity to invoke nonradial outflow to explain the observations. In the region 3-6 solar radii the data imply a²/b ∼ r³, where a is the correlation length in the radial direction and b is the correlation length in the transverse direction. We point out that this behavior can result if both the transverse correlation length and the anisotropy ratio, a/b, increase linearly with r in that region.
- Publication:
-
Journal of Geophysical Research
- Pub Date:
- 1968
- DOI:
- 10.1029/JA073i023p07221
- Bibcode:
- 1968JGR....73.7221H