Outer scale of solar wind turbulence deduced from two-way coronal radio sounding experiments Original Research Article

Results of two-way mode coronal radio sounding experiments using the Helios-1,-2, Pioneer-10,-11, and Viking-1 spacecraft are presented. These observational data apply to the low-latitude solar wind during solar activity minimum. Enhancements of the Doppler scintillation variance were detected for spacecraft located closer to the effective scattering layer with respect to the variance measured for a more distant spacecraft at the same time and solar elongation. These enhancements can be explained by the assumption that the radio signal passes twice through the same solar wind density irregularities for close spacecraft but through uncorrelated irregularities when the heliocentric distance becomes too large. Estimates of the outer scale of solar wind turbulence at different heliocentric distances are found from a comparison of Doppler scintillations from near and distant spacecraft.