Latitudinal Variation of the Underlying Heliospheric Magnetic Field Direction: Comparison of the Ulysses First and Second Orbits

Abstract

We discuss the underlying direction of the heliospheric magnetic field measured by Ulysses in the latitude range 6° S-65° S by examining distributions of the magnetic field azimuthal angle with respect to the simple Parker spiral model. During the first Ulysses traversal of this latitude range in 1992 1994, while solar activity was declining, the shape of the distributions obtained at high latitudes in the fast solar wind differed from that at lower latitudes. In the present data set, obtained during rising solar activity, both field polarities are present at all latitudes and the peaks of the distributions agree with the predicted spiral direction to first approximation. However, compared to the first orbit, a significantly greater percentage of the observed field vectors have large deviations from the spiral direction.