The symmetry of the heliospheric current sheet as observed by Ulysses during the Fast Latitude Scan

Abstract

The position of the heliospheric current sheet is investigated, based on Ulysses observations during the fast latitude scan from the South pole (in September, 1994) to the North pole (in July, 1995). The location of the current sheet on the source surface was calculated by mapping back the magnetic field vectors measured by Ulysses along the solar wind flowline. The areas on the source surface occupied by the positive and negative sectors have been determined from the observations and no significant difference in the areas has been found. Thus, during the Ulysses fast latitude scan, the heliospheric current sheet had no significant latitudinal offset; the assumption of such an offset had been used on the interpretation of galactic cosmic ray fluxes measured aboard Ulysses. We use the previously published findings concerning the heliolatitude‐independence of the radial component of the heliospheric magnetic field and its approximately constant magnitude in the two solar hemispheres to argue that any north‐south asymmetry in the sector structure is unlikely, as there must be a flux balance between the different polarity sectors. The results are compared to the predictions of the Standford University models, based on photospheric observations, concluding that coronal models should be revised to account for Ulysses observations.