Bulletin of Taras Shevchenko National University of Kyiv. Astronomy, no. 67, p. 41-49 (2023)


Nina KONDRASHOVA, Ph.D (Phys. & Math.)
Mail Astronomical Observatory of NAS, Kyiv, Ukraine

Valery KRIVODUBSKIJ, DSc (Phys. & Math.)
Taras Shevchenko National University of Kyiv, Kyiv, Ukraine


Background. Under certain conditions, deep fluctuating magnetic fields lead to violations of Hale’s and Joy’s laws of observed magnetism on the surface of the Sun. These magnetic fluctuations can be excited by two qualitatively different mechanisms of a small-scale dynamo. The first mechanism is a macroscopic MHD dynamo, while the second mechanism is a classical MHD diffusion dynamo. An important difference between the two mechanisms is the percentage of observed anti-Hale sunspot groups (relative to the total number of sunspots) in solar cycle minima. In the case of the first mechanism, the percentage of anti-Hale groups does not depend on the phase of the cycle, while the specified percentage associated with the second mechanism should reach its maximum value in solar minima. To separate the minor contributions of the two named sources of magnetic fluctuations, the researchers proposed a theoretical test based on statistical analysis of observational data over long periods of time (Sokoloff, & Khlystova, 2010). According to the proposed test, the percentage of anti-Hale groups of spots increases during the minima of the cycles, which indicates the favor of the diffusion dynamo. In order to confirm the dominant contribution of the diffusion dynamo to the surface magnetism, this work investigates a specific anomalous active region near the solar minimum.

Methods. Macroscopic and classical MHD, which study the behavior of electromagnetic and hydrodynamic fields in turbulent plasma. Analysis of data from observations of the surface magnetism of the Sun.

Results. We investigated the evolution of the NOAA 13088/13102 active region observed on August 24, 2022, shortly after the cycle 25 minimum. For the analysis, data from observations using instruments installed on board space observatories were used. A feature was revealed, which consists in the deviation of the surface magnetic configuration of this active region from Hale’s law of the magnetic polarity of groups of spots and Joy’s law of the inclination of the axes of bipolar groups to the latitudinal direction. In addition, it was established that the active region of NOAA 13088/13102 is characterized by rather high flare activity.

Conclusions. We believe that the magnetic anomalies of the active region of NOAA 13088/13102 that we found were caused by the influence of magnetic fluctuations excited by the mechanism of the deep small-scale diffusion dynamo, since it is this source that gives the most noticeable contribution to the surface magnetism near the cycle minima. The detection and study of unusual anti-Hale’s AOs with increased eruptive activity, similar to NOAA 13088/13102, may find application in predicting periods of dangerous manifestations of space weather and in forecasting the dynamics of solar cycles.

Key words
Solar convective zone, magnetic fields, turbulent dynamo, sunspots, solar flares.


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