Persistent north–south asymmetry of the daily interplanetary magnetic field spiral

Abstract

We have studied the north–south asymmetry of interplanetary magnetic field (IMF) and plasma data taken near 1 AU during the 26‐year period 1965–1990. The IMF azimuthal component is larger in magnitude than the radial IMF component north of the current sheet, while the reverse of this effect is true south of the current sheet. This should produce an asymmetry in the IMF spiral with larger angle north of the current sheet than south of the current sheet. We find that the IMF spiral angle is larger north of the current sheet than south of the current sheet. We confirm this north–south asymmetry in the IMF spiral angle to be persistent, using three different criteria to define away and toward field days. The asymmetry is 3.0° ± 0.7° for “well‐defined” polarity days. The field azimuthal component is higher north of the current sheet than south of the current sheet, while the reverse is true for the solar plasma density.