Radial dependence of intermittency in the fast polar solar wind magnetic field using Ulysses

Abstract

The Ulysses spacecraft, in a polar orbit of the Sun, spent almost 3 years sampling the pure polar coronal fast wind at solar minimum between 1994 and 1996. Turbulence in coronal fast wind, unaffected by stream shears with slow solar wind, evolves more slowly than fast wind turbulence in the ecliptic and is a more homogenous system. However, it is still a highly intermittent and turbulent medium. We use the Castaing probability distribution to study the intermittent properties of the fast wind magnetic field components at different time lags within the inertial range and for the first time present results on how intermittency in the magnetic field components depends on radial distance from the Sun. We find that for all distances, the transverse magnetic field components are significantly more non-Gaussian than the radial component. We also find that non-Gaussian behavior at a given time lag increases with distance but that this can be explained by the corresponding extension of the inertial range to lower frequencies so that the non-Gaussianity is constant at the integral scale, agreeing with theoretical predictions. We also find that the rate at which non-Gaussian deviations propagate through the cascade decreases slightly with distance. Copyright 2003 by the American Geophysical Union.