Measurement of the North/South Asymmetry of the IMF Spiral: Dependence Upon Heliocentric Distance

C. W. Smith and J. W. Bieber

Proceedings of the 21st International Cosmic Ray Conference (Adelaide), 5, 304-307 (1990)

Abstract:

Previous work by Bieber (1988) has shown that the interplanetary magnetic field (IMF) spiral at 1 AU displays a north/south asymmetry with the IMF spiral more tightly wound north of the heliospheric current sheet than south of it, the difference being 3.1 degrees +/- 1.1 degrees. We have extended that analysis to include observations at .7 AU and from 1 AU to 17 AU. The inner heliospheric observations generally confirm the 1 AU results. Observations in the outer heliosphere reveal a much greater degree of asymmetry than was observed at 1 AU with a reversal in sign. The asymmetry is so extreme that ``away'' fields during some periods typically have a component pointing back toward the sun. Interpretation of this result in terms of a simple modification of the Parker winding angle does not appear to be possible. Whatever its origin, the asymmetry of the IMF spiral may help to explain the north/south difference seen in the solar modulation of galactic cosmic rays.