ANISOTROPY OF INERTIAL RANGE TURBULENCE IN THE POLAR HELIOSPHERE

A variance analysis of high frequency, inertial range fluctuations in the polar magnetic field as recorded by the Ulysses spacecraft indicates that they are largely transverse to the ambient magnetic field direction and highly anisotropic. Despite large changes in the mean field direction caused by the presence of large amplitude Alfven waves, alignment of minimum variance vectors of 5 minute intervals of linearly detrended data with the mean field direction was good, with around 75% of minimum variance vectors lying within 26 degrees of the mean field direction during a typical 5 day interval. Such fluctuations transverse to the mean field have anisotropies - the ratio of power transverse to the field to that parallel - of around 30. We find a small tendency for the field-transverse fluctuations to become more isotropic with distance. Intervals whose minimum variance directions are not field-aligned appear to be indicative of a significantly different: type of fluctuations, with higher total variances and lower anisotropy.