부산대학교 도서관

Coronal radio sounding experiments with the Ulysses spacecraft at superior conjunction provided numerous opportunities for simultaneous observations of the downlink signals at two widely-spaced ground stations. In some instances the duration of these observations extended for up to four hours, thereby allowing studies of solar wind turbulence dynamics at spatial scales comparable with the corona-projected distance between ground stations (a few thousand km). The frequency and phase fluctuations produced by electron density inhomogeneities are normally quite well correlated on these scales. The spectral index of the temporal frequency fluctuation spectra varied over a wide range during the observations. The cross-correlation coefficient reached maximal values (≈ 0.5) when the spectral index was high (≈ 1), but no correlation could be detected when the spectral index became small (< 0.4). Similar behavior in many of the data sets implies that this is a common, if not permanent, feature of the solar wind. Possible reasons for the fluctuation decorrelation are analysed. The decorrelation at heliocentric distances ≈ 10 R⊙ most likely results from continual deformation of the solar wind density irregularities during their motion across the radio ray paths. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]