Solar Implications of [ITAL]Ulysses[/ITAL] Interplanetary Field Measurements

Abstract

Recent observations by the Ulysses magnetometer team have shown that the strength of the radial interplanetary field component, |B|, is essentially independent of latitude, a result which implies that the heliospheric currents are confined entirely to thin sheets. Using such a current sheet model, we extrapolate the observed photospheric field to 1 AU and compare the predicted magnitude and sign of B_r with spacecraft measurements during 1970-1993. Approximate agreement can be obtained if the solar magnetograph measurements in the Fe I λ5250 line are scaled upward by a latitude-dependent factor, similar to that derived by Ulrich from a study of magnetic saturation effects. The correction factor implies sharply peaked polar fields near sunspot minimum, with each polar coronal hole having a mean field strength of 10 G.