Determination of anisotropic magnetic energy spectra using Ulysses data

Observational results from a wavelet analysis of Ulysses magnetic field fluctuations are presented, indicating that the magnetic energy spectrum in the solar wind is anisotropic. The wavelet technique enables accurate scale-dependent determination of the local magnetic field direction, $ \bar{\bf{B}} $. The frequency power spectrum of magnetic field fluctuations is calculated, as a function of the angle $ \theta_{\bar{B}} $ between $ \bar{\bf{B}} $ and the radial (i.e., measurement) direction. Nine different 30-day intervals (of 1 second data) are analyzed, and in each case the spectral slope is $\approx 5/3$ for angles not ``close'' to the field-parallel direction (i.e., $0^\circ$), but transitions smoothly to $\approx 2$ as $\theta_{\bar{B}} \to 0^\circ$. Discussion of these results in terms of anisotropic models of MHD turbulence is also presented.