Time variations of the tangential velocity component in the Evershed effect.

Observations of the tangential velocity component in the Evershed effect (torsional oscillations of sunspots) are reported. The spectral composition of the radial-velocity signals from two penumbral areas at positions symmetric about the umbra was investigated for six sunspots. The selected fields were on a line perpendicular to the direction to the center of the Sun's image, i.e., the rotational velocities of the gas in the sunspot were measured. The observations were made in the lines Fe I λ543.45 nm and H_β 486.13 nm. The results of the study confirm the existence of torsional oscillations of sunspots at photosphere level with a period of about an hour. These oscillations were measured for the first time at chromosphere level (period about 30 min). It is concluded from observations of two sunspots over three and four days that torsional oscillations with a period of several days occurred in these sunspots.