THE ROLE OF MACROSCOPIC TURBULENT DIAMAGNETISM IN ENSURING LONG-TERM STABILITY OF SUNSPOTS
DOI:
https://doi.org/10.18524/1810-4215.2020.33.216449Ключові слова:
sunspots, magnetic fields, turbulence, convective overshoot layer, macroscopic turbulent diamagnetismАнотація
We investigated the role of macroscopic
turbulent diamagnetism in ensuring the long-term stability
of the equilibrium state of the sunspots. The physical
meaning of macroscopic diamagnetism of turbulent
plasma is expulsion of a large-scale magnetic field from
areas with increased turbulence intensity to areas with
reduced turbulence. We follow the idea of Krause &
Rüdiger (1975) that a strong magnetic field of a sunspot
modifies the structure of turbulence in spot umbra, so it
becomes two-dimensional. In addition, we take into account
the strong magnetic suppression of turbulence in the spot,
where it becomes less intense than the turbulent convection
around the spot. As a result, a relatively thin transitional
vertical layer of permeable convection (convective overshot
layer) should be formed between these sections, in which
the intensity of turbulent pulsations decreases noticeably
in the transverse direction during the transition from the
convection section to the spot. In this permeable convection
layer, the effect of turbulent diamagnetic displacement of
the magnetic field from the convection region to the sunspot
occurs. Owing to the two-dimensional turbulent diffusion,
the magnetic field of the spot spreads outwards, while the
intense turbulent pulsations in the convection region return
the magnetic field in the opposite direction, back to the
spot. Therefore, these two oppositely directed processes of
magnetic field transfer in the horizontal plane compete
with each other. As a result, the magnetic fields that are
transferred due to turbulent diffusion outward from the
sunspot will be thrown backward into the spot due to strong
external turbulent convection. In our opinion, this effect
should ensure long-term stability of the equilibrium state
of the magnetic field of sunspots and support them in the
form of isolated vertical unipolar magnetic force tubes.
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