Angular distribution of discontinuity normals of the interplanetary magnetic field

High time resolved (6 s) magnetic field data from the Helios-1 and Ulysses spacecrafts were used to investigate MHD discontinuities in the heliosphere. The identification of discontinuities was based on the rotation of the field vectors relative to the distance to the plasma in which the vectors were supposed to be frozen. In order to obtain the real thickness of the discontinuity transition region, the surface normal of discontinuities were calculated by both the minimum variance and cross-product methods. We found an anisotropy in the angular distribution of the discontinuity surface normals in the heliosphere where the average interplanetary magnetic field is close to radial. It is an indirect evidence that most of the discontinuities are tangential rather than rotational ones. This result is also supported by the fact that the Minimum Variance and Cross-Product methods gave similar results for the determination of the surface normals. ((c) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)