Bulletin of Taras Shevchenko National University of Kyiv. Astronomy, no. 59, p. 29-34 (2019)

Electrical conductivity of plasma in magnetic configurations of the sunspots

V. Krivodubskij, Dr. Sci.

Astronomical Observatory of Taras Shevchenko National University of Kyiv, Kyiv 


Abstract

The main problem of electromagnetic models of flares on the Sun is that in conditions of high electrical conductivity of the solar plasma it is difficult to provide an effective energy release as a result of Joule dissipation of currents in the “kernel of the flare”. In order to explain the rapid dissipation of electric currents in the “kernel of the flare”, we, within the framework of macroscopic magnetohydrodynamics, have considered the effect of reducing the electrical conductivity in a turbulent environment. The idea of redistribution of the electrical conductivity in groups of sunspots with complex magnetic field configuration is proposed. The proposed concept for the redistribution of electrical conductivity is based on the following physical effects and well-known observational conditions in the solar atmosphere. 1. Decreasing of the electrical conductivity (increase in the resistivity) in a turbulent environment. 2. Magnetic inhibition of the turbulence under the influence of magnetic fields. 3. Excitation of a large-scale electric field by macroscopic movements of the plasma in the photosphere in the presence of a weak general magnetic field of the Sun (photosphere dynamo). 4. Observed spatial heterogeneous structure of magnetic configurations in the vicinity of groups of sunspots, which leads to the formation of the current layers with the zero (neutral) magnetic fields. In the places of the zero magnetic field in the photosphere (which correspond to the “kernel of the flare”), where there is no suppression of turbulence by magnetism, the conductivity is turbulent in the nature. At the same time, in the vicinity of the sunspots outside the “kernel of the flare”, turbulent motions are largely suppressed by strong magnetic fields (B ≈ 3000 G), which almost alleviates the effect of the influence of turbulence on the conductivity of the plasma. Therefore, the electrical conductivity here will be gas-kinetic in the nature, the value of which greatly exceeds the turbulent conductivity. The turbulent conductivity calculated by us in the photosphere σ T ≈ 5 ⋅ 108 CGSE turned out to be 2-3 orders of magnitude smaller than the gaskinetic conductivity σ ≈ 1011 CGSE (in the places of strong magnetic fields). The discovered areas of the abnormal reduced turbulent conductivity in the places of the zero magnetic lines of complex configurations of the sunspot groups can contribute to the efficient dissipation of the electric currents, which provides efficient thermal energy release of the flares. The problem of circulation of two currents in the electric circuit of the corona-photosphere is briefly considered. According to the model of the photosphere dynamo, the convective movements on the photosphere level excite an electric field of magnitude E0 ≈ 10-4 CGSE. In this case, in external areas (in relation to the region of the “kernel of the flare”) of the electric circuit of the corona-photosphere in the places of strong magnetic fields, where the turbulence is almost suppressed, the value of the current will be ja = σ E0 ≈ 107 CGSE. At the same time, in the area of the “kernel of the flare”, where neutral magnetic fields do not affect turbulence, the current value will be much smaller: jT ≈ σ T E0 ≈ 5 ⋅ 104 CGSE. The existence of two sections with different currents in the electric circle of the corona-photosphere may contribute to the spatial division of charges, which in turn may be useful in the further development of the electromagnetic models of the flare.

Key words
Solar flares, magnetic fields, sunspots, turbulent electrical conductivity, electric currents

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DOI: https://doi.org/10.17721/BTSNUA.2019.59.29-34