Polar flux imbalance at the sunspot cycle minimum governs hemispheric asymmetry in the following cycle

Abstract

Aims. Hemispheric irregularities of solar magnetic activity is a well-observed phenomenon, the origin of which has been studied through numerical simulations and data analysis techniques. In this work we explore possible causes generating north-south asymmetry in the reversal timing and amplitude of the polar field during cycle minimum. Additionally, we investigate how hemispheric asymmetry is translated from cycle to cycle. Methods. We pursued a three-step approach. Firstly, we explored the asymmetry present in the observed polar flux and sunspot area by analysing observational data of the last 110 years. Secondly, we investigated the contribution from various factors involved in the Babcock–Leighton mechanism to the evolution and generation of polar flux by performing numerical simulations with a surface flux transport model and synthetic sunspot input profiles. Thirdly, translation of hemispheric asymmetry in the following cycle was estimated by assimilating simulation-generated surface magnetic field maps at cycle minimum in a dynamo simulation. Finally, we assessed our understanding of hemispheric asymmetry in the context of observations by performing additional observational data-driven simulations. Results. Analysis of observational data shows a profound connection between the hemispheric asymmetry in the polar flux at cycle minimum and the total hemispheric activity during the following cycle. We find that the randomness associated with the tilt angle of sunspots is the most crucial element among diverse components of the Babcock–Leighton mechanism in resulting hemispheric irregularities in the evolution of polar field. Our analyses with dynamo simulations indicate that an asymmetric poloidal field at the solar minimum can introduce significant north-south asymmetry in the amplitude and timing of peak activity during the following cycle. While observational data-driven simulations reproduce salient features of the observed asymmetry in the solar cycles during the last 100 years, we speculate that fluctuations in the mean-field α-effect and meridional circulation can have finite contributions in this regard.

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

“…Other authors have identified this persistence in asymmetry when integrated over a solar cycle (Li et al, 2001;Leussu et al, 2016). In this context of possible longer-term memory we note that Bhowmik (2019) found from observations that asymmetry in polar fluxes at sunspot minimum was reflected in sunspot asymmetry in the subsequent cycle. The paradox of random fluctuations generating long-term trends in sunspot asymmetry was modelled by Nepomnyashchikh et al (2019) who used random perturbations to tilt angle and yet generated trends that lasted several solar cycles.…”

Does the mean-fieldαeffect have any impact on the memory of the solar cycle?

“…However, two different proposals exist in the literature for the poloidal field generation-one involves the decay and dispersal of bipolar magnetic regions at the solar surface, termed as the Babcock-Leighton mechanism (Babcock 1961;Leighton 1969) and the other evokes strong helical turbulence inside the solar convection zone, known as the mean-field α effect (Parker 1955;Steenbeck et al 1966). In recent years, dynamo models based on the Babcock-Leighton mechanism have been successful in explaining different observational aspects regarding solar activity (Dikpati & Charbonneau 1999;Nandy & Choudhuri 2002;Choudhuri et al 2004;Nandy et al 2011;Choudhuri & Karak 2012;Bhowmik & Nandy 2018;Hazra & Nandy 2019;Bhowmik 2019). Recently, data-driven 2.5D kinematic dynamo models and 3D kinematic solar dynamo models have also been developed to study different observational aspects regarding solar activity (Brun 2007;Jouve et al 2011;Yeates & Muñoz-Jaramillo 2013;Hung et al 2017;Hazra et al 2017;Karak & Miesch 2017;Hazra & Miesch 2018;Kumar et al 2019).…”

Solar Cycle Evolution of Filaments over a Century: Investigations with the Meudon and McIntosh Hand-drawn Archives

“…We find the north-south asymmetry of filament numbers from the Meudon database is correlated with the north-south asymmetry of filament numbers from McIntosh data during the overlapping period with a Spearman rank correlation coefficient 0.50 with the confidence of 99.99%. This asymmetry in filament distribution may arise from the underlying asymmetry of magnetic field emergence associated with the solar dynamo mechanism (Passos et al 2014;Bhowmik 2019;Hazra & Nandy 2019) and (or) they might be related to hemispheric asymmetries in large-scale plasma flows (Lekshmi et al 2018(Lekshmi et al , 2019; these merit further theoretical investigations.…”

“…Generation of magnetic fields in the Sun is not symmetric in two hemispheres (Bhowmik 2019). Naturally features like sunspots, filaments, plages, etc., which are magnetic in nature show north-south asymmetry.…”