Evolution of the Sun's Polar Fields and the Poleward Transport of Remnant Magnetic Flux

摘要

Synoptic magnetograms and relevant proxy data were analyzed to study the evolution of the Sun's polar magnetic fields. The time-latitude analysis of large-scale magnetic fields demonstrates cyclic changes in their zonal structure and the polar field buildup. The time-latitude distributions of the emergent and remnant magnetic flux enable us to examine individual features of recent cycles. The poleward transport of predominantly following polarities contributed much of the polar flux and led to polar field reversals. Multiple reversals of dominant polarities at the Sun's poles were identified in Cycles 20 and 21. Triple reversals were caused by remnant flux surges of following and leading polarities. The time-latitude analysis of solar magnetic fields in Cycles 20 – 24 revealed zones that are characterized by a predominance of negative (non-Joy) tilts and by the appearance of active regions that violate Hale's polarity law. The decay of non-Joy and anti-Hale active regions results in remnant flux surges that disturb the usual order in magnetic flux transport and sometimes lead to multiple reversals of polar fields. The analysis of local and large-scale magnetic fields and their causal relation improved our understanding of the Sun's polar field weakening.