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"Formation of large-scale
inhomogeneous magnetic structures in a turbulent convection". N. Kleeorin
(Ben-Gurion University of Negev, Abstract: Magnetic fluctuations generated by a tangling of the mean magnetic field
by velocity fluctuations are studied in a developed turbulent convection with
large magnetic Reynolds numbers. We show that the energy of magnetic
fluctuations depends on magnetic Reynolds number only when the mean magnetic
field is smaller than $B_{\rm
eq} / 4 {\rm Rm}^{1/4}$, where $B_{\rm eq}$ is the equipartition mean
magnetic field determined by the turbulent kinetic energy and ${\rm Rm}$ is magnetic
Reynolds number. Generation of magnetic fluctuations in a turbulent
convection with a nonzero mean magnetic field results in a decrease of the
total turbulent pressure and may cause formation of the large-scale
inhomogeneous magnetic structures even in an originally uniform mean magnetic
field. This effect is caused by a negative contribution of the turbulent
convection to the effective mean Lorentz force. The
inhomogeneous large-scale magnetic fields are formed due to the excitation of
the large-scale instability. The energy for this instability is supplied by
the small-scale turbulent convection. The discussed effects might be useful
for understanding the origin of the solar nonuniform
magnetic fields, e.g., sunspots. |