On the possibility of investigation of the magnetic field structure in subphotospheric layers of the Sun ON observations of sunspot torsional oscillations
The method of investigations of the magnetic field structure in subphotospheric layers of the Sun has been developed. Observational results on the torsional oscillations of sunspots formed the basis for this method. Characteristics of torsional oscillations were obtained on the longitudinal magnetic and velocity fields, observed in the photospheric Fe i λ5253 Å line of seven single sunspots. Parameters of torsional oscillations and magnetic tubes in deep layers were determined. The radius of cross-section of a magnetic flux tube forming a sunspot is the greatest near the solar surface and is approximately the same as the radius of a sunspot umbra. In deeper layers it decreases rather rapidly. The longitudinal electric current appearing in the magnetic tube changes the direction with the period of torsional oscillations. The intensity of the longitudinal magnetic field in the magnetic tube increases with depth. The Alfven wave velocity averaged over length of a magnetic tube is tens and hundreds times less than the same velocity in a sunspot umbra. It decreases with increase of the period of oscillations. Decreasing of the Alfven wave velocity leads to increasing of a twisting angle of magnetic field lines.
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