Heliospheric sector boundaries: Single or multiple?

Abstract

Solar wind data were examined for a period when the Ulysses spacecraft moved roughly parallel to the boundary between inward and outward interplanetary fields at a solar distance of 1.4 AU. Multiple crossings of the magnetic sector boundary were observed. Three tests were used to evaluate whether or not the crossings were due to multiple crossings of a single surface or single crossings of separate surfaces: (1) a correlation between the latitude and longitude directions of the normals to the surface, (2) the radius of curvature of the surface calculated from consecutive crossings, and (3) the variation of plasma parameters across the surfaces. Both multiple crossings of a single rippled surface and single crossings of multiple boundary surfaces were observed.