Outer scale of coronal turbulence near the sun

Abstract

Radio frequency fluctuations have been recorded using the Galileo carrier signal during the spacecraft's solar conjunctions. On these occasions the solar proximate point along the radio ray path to Earth ranged from 7 to 80 R ⊙. Regions of low-speed solar wind (equatorial streamer belt) were investigated in 1995/96. Temporal power spectra and variances of the frequency scintillations, and in some cases estimates of the speeds of large-scale density irregularities, have been computed. Owing to the exceptionally high stability of the radio signals, the range of the Doppler scintillation power spectra could be extended down to unprecedentedly low frequencies (∼0.01 mHz). Some of the Galileo spectra display a low-frequency turnover at frequencies ∼0.1 mHz that might be evidence of the density turbulence outer scale in the inner slow solar wind.