Influence of non-potential coronal magnetic topology on solar wind models

Abstract

By comparing a magneto-frictional model of the low coronal magnetic field to a potential field source surface model, we investigate the possible impact of non-potential magnetic structure on empirical solar wind models. These empirical models (such as Wang-Sheeley-Arge) estimate the distribution of solar wind speed solely from the magnetic field structure in the low corona. Our models are computed in a domain between the solar surface and 2.5 solar radii, and are extended to 0.1 AU using a Schatten current sheet model. The non-potential field has a more complex magnetic skeleton and quasi-separatrix structures than the potential field, leading to different sub-structure in the solar wind speed proxies. It contains twisted magnetic structures which can perturb the separatrix surfaces traced down from the base of the heliospheric current sheet. A significant difference between the models is the greater amount of open magnetic flux in the non-potential model. Using existing empirical formulae this leads to higher predicted wind speeds for two reasons: partly because magnetic flux tubes expand less rapidly with height, but more importantly because more open field lines are further from coronal hole boundaries.