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

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 the solar activity. The magnetic field from a Babcock–Leighton dynamo model generally agrees with these observations.

Synthetic solar cycle for active regions violating the Hale's polarity law

“…This period is known as the time of the polar field reversal and building the polar field that seeds the new cycle. The increased number and percentage of anti-Hale ARs at that time show that the role of such groups in the recovering of the global poloidal field may indeed be significant (Hazra et al 2017;Karak & Miesch 2018;Mordvinov & Kitchatinov 2019;Mordvinov et al 2022). The enchanced percentage of the anti-Hale ARs on the diagram is observed when the toroidal magnetic field is weakend (the edges of the time-latitude diagram and area near oncoming solar minimum).…”

“…ARs) play a significant role in deepening our understanding about some essential aspects of solar activity in such as the role of the turbulent component of dynamo on different scales (Stenflo & Kosovichev 2012;Sokoloff et al 2015), formation of magnetic flux tubes (López Fuentes et al 2000, 2003Nelson et al 2013) and especially about the intricasies involved with the polar field reversals (Hazra et al 2017;Karak & Miesch 2018;Mordvinov & Kitchatinov 2019;Mordvinov et al 2022). Also the knowledge gained in such studies help us to predict the characteristics of upcoming solar cycle which has a very important practical implication for the rapidly growing space and satellite industry (Mouradian & Soru-Escaut 1993;Nagy et al 2017Nagy et al , 2019.…”

Application of historic datasets to understanding open solar flux and the 20th-century grand solar maximum. 2. Solar observations

“…The synthesized magnetograms shown in Figure 7 confirm the broad predictions made previously by Mordvinov et al (2020) but give greater detail. Indeed the detail is now good enough for a plausible analysis of the causes and effects of individual poleward surges, of the kind carried out for actual magnetograph data (Lockwood et al, 2017;Mordvinov and Kitchatinov, 2019;Mordvinov et al, 2021).…”

Physical link of the polar field build-up with the Waldmeier effect broadens the scope of early solar cycle prediction: Cycle 25 is likely to be slightly stronger than Cycle 24

“…This may be due to the fact that we are calculating the rise rate based on only first two years data (to make it consistent with the available data for Cycle 25). Furthermore, the polar field data are imperfect due to limited observations in the polar regions (Bertello et al 2014;Mordvinov et al 2022). Hence, the reliability of this relation cannot be endorsed with limited data.…”

“…It is because the generation of poloidal field involves some randomness, particularly due to scatter in the BMR tilts (Jiang et al 2014;Hazra et al 2017;Karak & Miesch 2017;Jha et al 2020) and the latitudinal positions of BMRs (Karak 2020). In fact, there is indication that the decline phase of the cycle (during which the polar field is built up after reversal) is more irregular having many anti-hale and non-Joy BMRs (Zhukova et al 2022;Mordvinov et al 2022), that can disturb the growth of the polar field considerably. Due to this inherent randomness in the Babcock-Leighton process, even if two cycles decay identically, their corresponding polar field can build up differently.…”