The Large-Scale Structure of the Heliospheric Magnetic Field

Abstract

The heliospheric magnetic field, embedded in the solar wind, originates in the highly non-uniform magnetic structures of the solar corona. Its source function is not easily discernible, but a brief description of the photospheric and coronal fields can give an indication of its temporal and spatial boundary conditions. Direct observations of the interplanetary magnetic field have only been made in and near the solar equatorial plane. These have confirmed Parker’s original model as a good first approximation. The most significant feature of the equatorial structure is the current sheet separating the two polarity regions on the sun and extending deep into interplanetary space. This feature has been successfully modelled and remains the major achievement among efforts to relate solar and coronal structures to interplanetary observations. On the other hand, the heliolatitude dependence of the structure of the field remains unknown. The paper concludes with a model list of questions which will only be answered by the in situ observations planned during the forthcoming Ulysses mission.