The north-south asymmetry of the heliospheric current sheet: Results of an MHD simulation

A. V. Usmanov 1,2 and M. L. Goldstein 2

1 Department of Physics and Astronomy and Bartol Research Institute, University of Delaware, Newark, DE 19716

2 Code 673, NASA Goddard Space Flight Center, Greenbelt, MD 2077

A displacement of the heliospheric current sheet (HCS) southward of the helioequator by 10 degrees was suggested to explain the north-south asymmetry of the galactic cosmic rays observed by Ulysses during its first fast latitude scan in 1994-1995. Although the hypothesis was widely accepted in the scientific community, it was not directly supported by the measurements of the magnetic field on Ulysses, In addition, Erdos and Balogh (1998) argued that any north-south symmetry was unlikely as there should be a flux balance between the magnetic sectors with different polarity. Using a three-dimensional magnetohydrodynamic solar wind model, we show that indeed a north-south asymmetry of the solar magnetic field (that we simulate as a composition of dipole and quadrupole) is not translated into an asymmetry of the HCS. This is a result of the latitudinal redistribution of the magnetic fluxes that reduces the displacement of the HCS and brings the magnetic field strength on both sides of the HCS into balance. The process takes place in the region near the Sun where the magnetic field dominate the flow (approx. within 10-15 solar radii). At larger distances, where the magnetic field is relatively weak, the HCS can still experience displacement if there is a difference in
plasma pressure between the hemispheres.