Meridional flow and rotation of active regions

Abstract

Meridional flow and rotation are studied using high-resolution magnetograms taken during the year 1988 with the NSO Vacuum Telescope on Kitt Peak. Motions are determined by a two-dimensional crosscorrelation analysis of 107 pairs of consecutive daily observations. The analysis was done first with active regions included and repeated with active regions excluded. The difference between the two analyses provides an estimate of the motions of active regions. I find that active regions rotate slower than small magnetic features and that active regions show a meridional flow toward the mean latitude of activity.