north‐south asymmetry of the interplanetary magnetic field spiral

An analysis of 20 years of interplanetary magnetic field (IMF) data reveals that the IMF spiral is more tightly wound north of the heliospheric current sheet than it is south of the current sheet, the difference in mean spiral angle being some 3.1° ± 1.1° at the orbit of Earth. A concurrent analysis of plasma data indicates that this asymmetry does not originate with a corresponding asymmetry in solar wind speed. Currently available information suggests that asymmetric solar rotation may give rise to part of the observed spiral asymmetry but probably not all of it. Whatever its origin, the asymmetry of the spiral may help explain north‐south differences seen in the solar modulation of galactic cosmic rays.