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

TL;DR

This study constructs a synthetic solar cycle from multiple observational periods to analyze anti-Hale active regions, revealing their connection to the solar dynamo, their cycle-dependent behavior, and their potential role in polar field reversal.

Contribution

The paper introduces a novel method to compile a synthetic solar cycle from multiple data sets, enabling detailed analysis of anti-Hale active regions and their relation to the solar magnetic cycle.

Findings

Anti-Hale ARs follow the solar cycle and are evenly spread in time and latitude.

The number and percentage of anti-Hale ARs increase in the second half of the cycle.

Anti-Hale ARs are more prevalent near the edges of the butterfly diagram and during solar minima.

Abstract

Long observational series for bipolar active regions (ARs) provide significant information about the mutual transformation of the poloidal and toroidal components of the global solar magnetic field. The direction of the toroidal field determines the polarity of leading sunspots in ARs in accordance with the Hale's polarity law. The vast majority of bipolar ARs obey this regularity, whereas a few percent of ARs have the opposite sense of polarity (anti-Hale ARs). However, the study of these ARs is hampered by their poor statistics. The data for five 11-year cycles (16-18 and 23,24) were combined here to compile a synthetic cycle of unique time length and latitudinal width. The synthetic cycle comprises data for 14838 ARs and 367 of them are the anti-Hale ARs. A specific routine to compile the synthetic cycle was demonstrated. We found that, in general, anti-Hale ARs follow the solar cycle and are spread throughout the time-latitude diagram evenly, which implies their fundamental connection with the global dynamo mechanism and the toroidal flux system. The increase in their number and percentage occurs in the second part of the cycle, which is in favour of their contribution to the polar field reversal. The excess in the anti-Hale ARs percentage at the edges of the butterfly diagram and near an oncoming solar minimum (where the toroidal field weakens) might be associated with strengthening of the influence of turbulent convection and magnetic field fluctuations on the arising flux tubes. The evidence of the misalignment between the magnetic and heliographic equators is also found.