Evolution of the Sun's activity and the poleward transport of remnant magnetic flux in Cycles 21--24

TL;DR

This study analyzes the evolution of solar magnetic activity across Cycles 21 to 24, focusing on how remnant magnetic flux surges influence polar field reversals and overall solar magnetic field restructuring.

Contribution

It provides a detailed analysis of magnetic flux surges and their role in polar reversals, highlighting the impact of non-standard active regions and linking observations with Babcock-Leighton dynamo models.

Findings

Remnant flux surges are critical in polar field reversals.

Unusual active regions affect magnetic flux transport.

Surges can link consecutive solar cycles.

Abstract

Detailed study of the solar magnetic field is crucial to understand its generation, transport and reversals. The timing of the reversals may have implications on space weather and thus identification of the temporal behavior of the critical surges that lead to the polar field reversals is important. We analyze the evolution of solar activity and magnetic flux transport in Cycles 21--24. We identify critical surges of remnant flux that reach the Sun's poles and lead to the polar field reversals. We reexamine the polar field buildup and reversals in their causal relation to the Sun's low-latitude activity. We further identify the major remnant flux surges and their sources in the time-latitude aspect. We find that special characteristics of individual 11-year cycles are generally determined by the spatiotemporal organization of emergent magnetic flux and its unusual properties. We find a complicated restructuring of high-latitude magnetic fields in Cycle~21. The global rearrangements of solar magnetic fields were caused by surges of trailing and leading polarities that occurred near the activity maximum. The decay of non-Joy and anti-Hale active regions resulted in the remnant flux surges that disturbed the usual order in magnetic flux transport. We finally show that the leading-polarity surges during cycle minima sometimes link the following cycle and a collective effect of these surges may lead to secular changes in solar activity. The magnetic field from a Babcock--Leighton dynamo model generally agrees with these observations.