Abstract
Digitized Mount Wilson sunspot data from 1917 to 1985 are analyzed to examine meridional motion and rotation properties as a function of latitude and distance (ξ) from the average latitude of activity (ξ0) in each hemisphere. Latitude dependence similar to previous results is found, but only for spot groups whose areas are decreasing from one day to the next. A previous study of active region magnetic fields, using this technique of motions as a function of the average latitude of activity, had shown meridional motions on average toward ξ0. In this analysis of spot data some evidence is seen for motion away from ξ0, with some slight evidence for faster rotation equatorward of ξ0 and slower motion poleward of ξ0, similar to the torsional oscillation phenomenon. For reasons that are not clear, both of these effects are significantly more pronounced for sunspot groups whose areas are decreasing.
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