LARGE-SCALE SOLAR PLASMA ROTATION AROUND STABLE SUNSPOTS

Motions of slowly evolving sunspots and the rotation velocity of the p lasma around them were determined within periods of one to three weeks each year from 1990 until 1992. The sunspots were divided into two cl asses depending on the size and number of proceeding and/or following umbrae. Most of the sunspots were of Zurich type H, too large and comp lex sunspots were rejected. The main aim was a determination of plasma and sunspot velocities within larger fields of activity and a search for special patterns of plasma flows, which may be caused by interacti on of the magnetized and unmagnetized plasmas. Around a total of 34 su nspots about 130 plasma velocity fields with sizes of about 120 by 70 arcseconds could be scanned. Within these fields the plasma rotation v elocity was determined using the non-split solar spectral line at 5576 angstrom with respect to laboratory iodine lines for an array of 400 by 240 points. The averaging of sub-fields +5 degrees in longitude (we st) of the sunspots compared with those -5 degrees (east) of the sunsp ots showed a difference of 50 m/s to 70 m/s for the mean values with t he same sign and about the same values for the two classes of sunspots selected. The amount of this determined asymmetry of the plasma rotat ion velocities in longitude depends on the excess rotation velocity of the sunspots as compared to the mean plasma rotation velocity at the latitudes where the sunspots were observed. While no dependence on the longitude distribution of the sunspots could be found, there is for b oth classes of sunspots a more pronounced asymmetry of the plasma rota tion velocity in the southern as compared to the northern hemisphere. Systematic errors are discussed and excluded. Some attempts are given to explain the new findings.