Effect of coronal magnetic fields on the formation of the solar wind from radio polarization occultation data

An analysis of radio occultation of the near-solar plasma using linearly po larized S-band (2.3 GHz) signals from the HELIOS-1 and HELIOS-2 spacecraft is presented. Fluctuations in the Faraday rotation of the plane of polariza tion were measured simultaneously at three widely spaced ground stations of the NASA Deep Space Network at Canberra, Madrid, and Goldstone. The tempor al energy spectra of the Faraday-rotation fluctuations (FRF) were obtained using measurements in 1981 and 1983 for heliocentric distances R = (3-12)R- S (R-S is the solar radius). We have studied the dependences of the shape a nd variance of the FRF spectra on heliocentric distance. The power-law inde x for the two-dimensional FRF spatial spectrum is close to beta = 2 for hel iocentric distances R = (3-6)R-S, and decreases with distance from the Sun, reaching the value beta = 1.2 at R = 10R(S). Comparison with earlier measu rements of the power-law index beta' for radio-occultation phase-fluctuatio n spectra shows that beta congruent to beta' when R=(3-6)R-S and beta < bet a' congruent to 2 at larger distances, The time lag between the FRF for dif ferent receiving stations was measured using a cross-correlation analysis, enabling determination of the velocities of the irregularities, which are i n good agreement with the expected Alfven speed. The correlation between te mporal variations of the fluctuation intensity and the time lag is studied. The FRFs are primarily determined by Alfven waves. The solar wind regime i n the acceleration region is governed by coronal magnetic fields.