Bulletin of Taras Shevchenko National University of Kyiv. Astronomy, no. 72, p. 17-32 (2025)
ADVANCES IN TURBULENT DYNAMO MAGNETIC CYCLE OF THE SUN
Valery KRIVODUBSKIJ, DSc (Phys. & Math.)
ORCID ID: org/0000-0001-7655-8121
e-mail: krivod2@uk.net, krivod@knu.ua
Taras Shevchenko National University of Kyiv, Kyiv, Ukraine
Abstract
Background. In the mid-1970s, a new direction of theoretical research into the cyclicity of the Sun’s global magnetism was initiated at the Astronomical Observatory based on the theory of the turbulent dynamo, built within the framework of macroscopic magnetohydrodynamics (MHD). Observations show that the poloidal and toroidal components of the Sun’s global magnetic field cyclically change in magnitude and polarity in antiphase with a period of about 22 years, called the Hale magnetic cycle. The most widespread belief among researchers is that the governing mechanism of the magnetic cycle is the αΩ dynamo model, which is based on the joint action of spiral turbulence and internal differential rotation in the solar convective zone (SCZ). The αΩ dynamo model describes magnetic cyclicity due to two basic effects: generation of a toroidal field with poloidal differential rotation (Ω effect) and inverse transformation of the toroidal field into a new poloidal field of opposite orientation caused by spiral turbulent convective motions (α effect). Studies in the last years of the last century have shown that the physical conditions in the depths of the SCC are favorable for the αΩ dynamo mechanism, which in the kinematic mode quite adequately describes the dynamics of the Sun’s magnetic cycle. However, a number of observed magnetic phenomena have remained unexplained for a long time. In view of this, the author conducted theoretical studies within the framework of macroscopic MHD aimed at eliminating the existing complications of the αΩ-dynamo model in explaining solar magnetic cyclicity. The article presents the results of these studies.
Methods. Macroscopic magnetohydrodynamics, which studies the behavior of global electromagnetic and hydrodynamic fields in turbulent plasma. Application of data modern helioseismological experiments on the internal rotation of the Sun.
Results. By incorporating non-linear turbulent effects from macroscopic MHD and using modern helioseismological data on the internal rotation of the Sun, key factors of the turbulent dynamo model have been modified. New applications include the updated α effect (change of sign of the helicity parameter in the deep layers of the SCC, magnetic alpha quenching, the effect of rotation on the helicity of turbulent motions), processes of turbulent rearrangement of magnetism (turbulent macroscopic diamagnetism, “negative magnetic buoyancy”, rotational ∇α effect), the effect of turbulence on the electrodynamic parameters of plasma (macroscopic electrical conductivity and magnetic permeability), physical processes in the layers of permeable convection and the radiant tachocline. The use of the reformed factors in the turbulent dynamo model made it possible to clarify a number of mysterious manifestations of the cyclic magnetism of the Sun.
Conclusions. By taking into consideration non-linear turbulent effects of macroscopic MHD and data from modern helioseismological experiments, the distribution of modified basic dynamo parameters in the RMS was calculated, which allowed us to expand the list of observed magnetic cyclicity phenomena that can be described within the framework of the improved αΩ dynamo model.
Key words
Turbulence, magnetic field, macroscopic magnetohydrodynamics, solar convective zone, radiant zone, overshoot, tachocline, helioseismology, αΩ dynamo, macroscopic turbulent diamagnetism, negative magnetic buoyancy, sunspots, solar magnetic cycle.
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