On the possibility of investigation of the magnetic field structure in subphotospheric layers of the Sun according to observations of sunspot torsional oscillations

ANALYSIS OFSOHO/MDI ANDTRACEOBSERVATIONS OF SUNSPOT TORSIONAL OSCILLATION IN AR10421

“…Formation and strengthening of the vortical structure of the transverse magnetic field of sunspots correspond well to the sunspot rotation calculated from photoheliograms (Gopasyuk 1965). Sunspot rotation is often accompanied by flares (Gopasyuk 1965;Gopasyuk & Lazareva 1986;Brown et al 2003;Zhang, Lin, & Zhang 2008).…”

“…It is related to the origin and evolution of sunspots and active regions. Rotation of sunspots around their centers has been observed by many authors (Abetti 1932;Maltby 1964;Gopasyuk 1965Gopasyuk , 1981Gopasyuk , 1982Brown et al 2001Brown et al , 2003Zhao & Kosovichev 2003;Nightingale et al 2004;Gopasyuk & Gopasyuk 2005). Formation and strengthening of the vortical structure of the transverse magnetic field of sunspots correspond well to the sunspot rotation calculated from photoheliograms (Gopasyuk 1965).…”

“…In all cases, there is a discrepancy, previously noticed by Gopasyuk (1981), between the azimuthal velocity defined from the white-light images and the rotation velocity of sunspots calculated from line-of-sight velocity ( Table 1). The rotational velocity calculated from the white-light images is tens of times smaller than the azimuthal velocity defined from the line-of-sight velocity.…”

“…The torsional motions of sunspots with a mean period of about six days were found from studies of photoheliograms, line-of-sight velocity in the photosphere, and H α images of active regions (Gopasyuk 1981(Gopasyuk , 1982. Further investigations showed that such motions are rather common and led to their interpretation in terms of sunspot torsional oscillations, which may represent an intrinsic feature of the sunspot state (Gopasyuk & Lyamova 1987).…”

A study of torsional sunspot motion

“…There are at least two basic techniques in the literature to measure sunspot rotations. A threedimensional velocity vector of plasma motion from its observed radial component is derived in [5] and other publications by the authors, while [6] have used a method that provides high-resolution maps of rotational speeds as a function of time, sunspot radius and angular coordinate. The latter ones use SOHO/MDI (Michelson Doppler Imager on board the Solar and Heliospheric Observatory) white-light images, from which they create time slices along rings around the sunspot centre by uncurling the original images.…”