The north-south asymmetry of active regions of different magneto-morphological types in solar cycles 23 and 24

Abstract

We used the elaborated earlier catalog of the magneto-morphological classes (MMC) of active regions (ARs) to study 2046 ARs of the solar cycle (SC) 23 and 1507 ARs of the SC24. According to empiric rules for sunspot groups (Hale’s polarity law, Joy’s law, etc.) and MMC, all ARs (except for unipolar spots) were sorted out between two categories: A-type – regular bipolar ARs; B-type – all the rest irregular ARs. We found that the number of both regular and irregular ARs follows the cycle with the Pearson’s correlation coefficient of 0.92 and 0.78, respectively. The regular ARs are distributed evenly between the two maxima of each cycle. The irregular ARs are also distributed evenly between the two maxima in the SC 23, however their number is enhanced in the second maximum of the SC 24. Both regular and irregular ARs exhibit strong north–south (N-S) asymmetry. The significance of asymmetry is confirmed using the Pearson’s χ-square test and one more test based on the normal approximation to a binomial distribution. During the two maxima of a cycle, the peaks in two hemispheres for both regular and irregular ARs number do not vary synchronously. This can be explained by the fluctuations in Babcock-Leighton mechanism. In general, there are more irregular ARs in the S-hemisphere in both cycles, which might be the result of an additional weakening of the toroidal field due to interplay between the dipole and quadrupole components of the global magnetic field.