Consequences of Treating the Solar Magnetic Field as a Dipole on the Global Structure of the Heliosphere and Heliosheath

Abstract

We investigate the effect of including the heliospheric current sheet on global modeling of the heliosphere. Due to inherent numerical dissipation in the current handling of the heliospheric current sheet, models have chosen to remove it to avoid numerical problems. We compare a model where the polarity of the Parker spiral is the same in both hemispheres (unipolar) to a dipole description of the solar magnetic field, with the magnetic and rotational axes aligned forming a flat heliospheric current sheet. The flat current sheet is pulled into the northern hemisphere, which reduces the magnetic field strength at the Voyager 1 trajectory over the last 22% of the heliosheath. The decrease in magnetic field intensity is transferred into the thermal energy of the plasma causing the dipole model to predict an entirely thermally dominated heliosheath; this is a stark contrast to the magnetically dominated region ahead of the heliopause in the unipole model. We find that the two-lobe structure of the solar wind magnetic field persists within the dipole model, with the flat current sheet not able to fully erode the magnetic tension force. However, there is a large amount of magnetic dissipation in the tail between the lobes, which affects the structure of the plasma in the region. Furthermore, the draped interstellar magnetic field in the dipole model is strongly affected by reconnection at the nose of the heliosphere, yielding a distinctly different draping pattern than that observed at Voyager 1.