Impact of rogue active regions on hemispheric asymmetry

Abstract

The solar dipole moment at activity minimum is a good predictor of the strength of the subsequent solar cycle. Through a systematic analysis using a state-of-the-art 2×2D solar dynamo model, we found that bipolar magnetic regions (BMR) with atypical characteristics can modify the strength of the next cycle via their impact on the buildup of the dipole moment as a sunspot cycle unfolds. In addition to summarizing these results, we present further effects of such "rogue" BMRs. These have the ability to generate hemispheric asymmetry in the subsequent sunspot cycle, since they modify the polar cap flux asymmetry of the ongoing cycle. We found strong correlation between the polar cap flux asymmetry of cycle i and the total pseudo sunspot number asymmetry of cycle i + 1. Good correlation also appears in the case of the time lag of the hemispheres of cycle i + 1.

Impact of nonlinear surface inflows into activity belts on the solar dynamo

“…Correlation between hemispheric asymmetry measures in fully stochastic simulations with and without inflows. These quantities are the polar cap flux asymmetry (∆Φ), the pSSN amplitude asymmetry (∆pSSN), and the timelag (∆T) between the cycle onsets in each hemisphere (for details see Nagy et al, 2019). In both panels dashed black line shows the ±1σ range around the linear fit to the asymmetry measures in the no-inflow simulations.…”

“…Linear correlarion between cycle maxima and dipole amplitude of the previous cycle. r ∆pSSN − Linear correlation between two asymmetry parameters: the asymmetry in hemispheric pSSN, the sunspot number asymmetry and that of the polar cap flux in the previous cycle (Nagy et al, 2019). r ∆T − Correlation between two asymmetry parameters: the time lag between hemispheric cycle onsets, and the asymmetry of polar cap flux in the previous cycle.…”

“…This indicates that the presence of inflows does not significantly slow down the flux transport towards the poles.Another potential impact of inflows concerns the hemispheric asymmetry in cycle characteristics. To quantify such effects we use the asymmetry parameters described inNagy et al (2019), namely: the polar cap flux asymmetry (∆Φ), the pSSN amplitude asymmetry (∆pSSN), and the timelag (∆T) between the cycle onset in each hemisphere.Figure 3shows correlation plots between these quantities, for the set of fully stochastic simulations. The corresponding linear correlation coefficient are given in the last two lines of…”

Dynamo Model for Nort-South Asymmetry of Solar Activity

“…In these equations, B r is the surface radial field, B is the bottom toroidal field, and the field argument mean the latitude where the field values were taken. The computed cycle minima were defined as the instants of the dipolar bottom toroidal field reversals at the latitude of 15 dynamo model by Nagy et al (2019). Though the correlation of Figure 8 is not as tight as the correlation between the polar and toroidal field strengths (cf.…”

“…Fluctuations in dynamo parameters can be responsible for different kinds of variability in solar activity cycles (see Chapter 7 in Charbonneau 2020, and references therein). Asynchronous fluctuations in the southern and northern hemispheres can cause asymmetry in magnetic activity (Schüssler & Cameron 2018;Karak et al 2018;Nagy et al 2019;Mordvinov et al 2020). Nepomnyashchikh et al (2019) suggested that NS asymmetry in solar activity results from equatorsymmetric fluctuations in the α-effect which transform the dominant dipolar dynamo mode into the quadrupolar mode.…”