Anisotropic structure of the solar wind in its region of acceleration

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Abstract Radio remote-sensing techniques have shown that the spectrum of irregularities of both the electron density and magnetic field are spatially anisotropic. New experimental data on the electron density irregularities have been obtained from simultaneous recordings of spacecraft signals at several widely-spaced ground stations. A cross-correlation analysis using phase and/or frequency fluctuations yields the outward flow speed of the irregularities. In contrast to earlier amplitude fluctuation measurements, correlation time lags across an intercontinental baseline may reach several tens of seconds. Temporal spectra of the amplitude fluctuations, on the other hand, are sensitive to both the velocity of the irregularities and the anisotropy coefficient. This technique was applied to experimental data recorded during the solar occultations of the Venera spacecraft. Typical values of the anisotropy coefficient are determined to be less than 2 at solar distances outside 15 R ⊙ and greater than 2 inside this distance. It is suggested that the radial dependence of the anisotropy is governed primarily by the coronal magnetic field strength.