Turbulent and fractal nature of solar and stellar magnetism
Abstract
Since the Babcock-Leighton phenomenological solar dynamo concept, a variety of solar dynamo models (in particular, mean-field dynamo models) were proposed to explain the 11-year cyclicity of solar magnetic activity. Similar magnetic cycles are observed on stars of the solar type. As the observational and computational facilities improved, ubiquitous irregularities in a broad range of scales appeared implying that the mean- field dynamo alone is not enough to explain the observed picture. A concept of small- field dynamo alone is not enough to explain the observed picture. A concept of small- scale near-surface dynamo was suggested to explain a magnetic carpet - population of mixed-polarity small magnetic elements in an undisturbed photosphere. Besides, an origin of irregularities on larger scales (scales of active regions, ARs) is still an open question. A question appears: is it necessary to introduce two independent mech- anisms to explain the magnetism on the Sun and stars? Using the magneto-graphic observations of the Sun, we have shown that solar magnetic field possesses properties of multifractality, its near-surface plasma evolves in a state of developed turbulence, the flux dispersion occurs in a regime of anomalous diffusion (super-diffusivity). Therefore, the process of magnetic field generation can be explained by unique dynamo mechanism operating as a non-linear dynamical dissipative system in a broad range of scales: from a typical AR size down to the size of smallest observable magnetic features. Pragmatic consequences can be as follows: i) strong fluctuations (e.g., flares) are unpredictable and not rare; ii) transport processes occur on a percolation cluster, which differs significantly from transport in continuous medium; iii) Gaussian statistics and central limit theorem are not applicable, individual probability density functions should be utilized for statistical estimates.
- Publication:
-
Astronomical and Astrophysical Transactions
- Pub Date:
- 2019
- Bibcode:
- 2019A&AT...31...63A
- Keywords:
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- Sun: magnetic fields;
- Sun: photosphere;
- Sun: sunspots;
- Sun: activity