ROTATION OF PLASMA IN SUNSPOTS ELDAR KHUTSISHVILI, TEIMURAZ KVERNADZE and MAJA SIKHARULIDZE Abastumani Astrophysical Observatory, 383762 Abastumani, Georgia (Received 10 December 1996; accepted 11 July 1997) Abstract. In this paper we present the results of a sunspot rotation study using Abastumani Astro- physical Observatory photoheliogram data for 324 sunspots. The rotation amplitudes vary in the 2–64 range (with maximum at 12–14 ), and the periods around 0–20 days (with maximum at 4–6 days). It could be concluded that sunspot rotations are rather inhomogeneous and asymmetric, but several types of sunspots are distinguished by their rotational parameters. During solar activity maximum, sunspot average rotation periods and amplitudes slightly increase. This can be affected by the increase of sunspot magnetic flux tube depth. So we can suppose that sunspot formation during solar activity is connected to a rise of magnetic tubes from deeper layers of the solar photosphere, strengthening the processes within the tube and causing variations in rotation. There is a linear relation between tilt-angle oscillation periods and amplitudes, showing higher amplitudes for large periods. The variations of those periods and especially amplitudes have a periodical shape for all types of sunspots and correlate well with the solar activity maxima with a phase delay of about 1 – 2 years. 1. Introduction The problem of solar rotation, and especially peculiar motion of the matter within sunspots, is one of the fundamental topics of the physics of the Sun, having a direct relation to the structure and stability of the Sun and solar activity. Recent increase of interest in the problem of sunspot rotation is caused by (i) the ascertaining that solar flare activity and sunspot rotation are connected (Gopasyuk, 1965, 1981, 1982, 1985; Gopasyuk and Lazareva, 1986), (ii) the discovery of rotational oscillation of sunspots with a period of about 6 days (Gopasyuk, 1981, 1982). Besides, it could be noted that the motion of the matter within sunspots is not clear, though it has remarkable velocities of rise and fall, but an insufficiently studied tangential component. Also the problem of the relationship between motions of the internal plasma and the magnetic fields of sunspots is not fully understood (Adam, 1963; Bumba, 1960; Miller, 1971; Zapp, 1963). At present there are a great many papers about the study of sunspot rotation. Kuklin and Stepanov (1963) came to the conclusion that ‘...it is possible to con- sider a complex picture of motion as a combination of sunspot magnetic field and plasma motion along magnetic field lines... magnetic field is not motionless within a sunspot.’ Subsequently Gopasyuk (1966, 1977) has supported the idea of sunspot magnetic field and plasma rising. Plasma motions within the sunspot penumbra were discovered in 1909 by Ever- shed (1909). A lot of investigators have studied this problem and detailed reviews of these papers can be found in Bray and Loughead (1964). According to Bray and Solar Physics 178: 271–283, 1998. c 1998 Kluwer Academic Publishers. Printed in Belgium.