Direct measurements of short-period torsional oscillations of sunspots. I. First results.

The first results of direct measurements of one of varieties of proper motions of sunspots, i. e., their torsional oscillations are presented. For three sunspots a study has been made of the spectral composition of line-of-sight velocity signals from two penumbra areas symmetric relative to the sunspot umbra near the limb. The penumbra areas chosen were located on a line perpendicular to the direction of the solar image. Main attention is paid to periods from one minute to several hours. The results reported here do not give convincing evidence for the presence of torsional oscillations of sunspots with a period of about an hour as detected by Gopasyuk, 1985 and Berton and Rayrode, 1985. Finally the authors discuss some typical features of quasi-five-minute oscillations in the sunspot penumbra and of non-periodic single velocity fluctuations in different penumbra areas.