HEMISPHERIC AND LONGITUDINAL ASYMMETRIES OF THE GLOBAL SOLAR MAGNETIC FIELD

摘要

Measurements of the heliospheric magnetic field (HMF) since 1960s have recently shown that the heliospheric current sheet (HCS) is systematically coned (or shifted) southward during solar minimum times, leading to the concept of a "bashful ballerina" . Recent solar observations in the last two solar cycles verify this HCS asymmetry and show that, during times of persistent HCS coning, the magnetic hemisphere dominant in the northern heliographic hemisphere attains a larger area but weaker intensity than in the south. The multipole expansion reveals a strong quadrupole term which is oppositely directed to the dipole term, implying that the Sun has a symmetric quadrupole S0 dynamo mode that oscillates in phase with the dominant dipole A0 mode. Moreover, HMF has a strong tendency to produce solar tilts that are roughly opposite in longitudinal phase. This implies is a systematic longitudinal asymmetry and leads to a "flip-flop" type behaviour in the dominant HMF sector whose period is about 3.2 years during the recent cycles. This agrees with the observed ratio of three between the activity cycle period and the flip-flop period of sun-like stars.