Small-Scale Anisotropy and Intermittence in High- and Low-Latitude Solar Wind

We study low- and high-latitude fast solar wind data from the Ulysses spacecraft from 1992 to 1994 using for the first time a systematic method to analyze the anisotropic content of the magnetic field fluctuations beyond second-order correlation functions. We investigate all available frequencies, 1-10^-6 Hz, for both high- and low-latitude data sets in which mean magnetic field points parallel and perpendicular to the mean flow, respectively, and we are able to quantify the relative importance of the anisotropic versus the isotropic fluctuations. We analyze, up to sixth order, longitudinal, transverse, and mixed magnetic field correlations. Our results show that strongly intermittent and anisotropic events persist even at high frequencies/small scales, indicating the absence of a complete recovery of isotropy. Our study shows for the first time the existence of intermittent anisotropic contributions at all scales in solar wind. Analyses of anomalous scaling of quantities that mix isotropic and anisotropic fluctuations, like longitudinal structure functions, may therefore be flawed by systematic uncontrolled errors. Anisotropic scaling properties are compatible for high- and low-latitude data, suggesting a universal behavior in spite of the different rate of evolution of the fast solar wind streams in the two environments.