The Proper Motion of Individual Sunspots

Abstract

The proper motions of 276 individual sunspots were observed with a triple-exposures method, and then analyzed. Their linear drifts give the mean motions (degree day−1), which, depending on the heliographic latitude B, are the differential rotation, ω(B) = 14.5 – 2.5sin2B, and the equatorward meridional flow, vB = −0.05sin 2B. The deviations of the linear drift from the mean motions have a small correlation between the longitudinal and latitudinal ones, which correspond to the equatorial acceleration. The deviations in longitude are clearly separated by the sunspot polarities. The average separation velocity between the preceding and following polarities is 52 m s−1. The drifts of individual sunspots corrected for the mean motion are the smallest for the Zürich GHJ class. However, they are fairly large and may influence the determination of the mean motion. Short-term variations appear as positional deviations from the linear-drift curve. These fast drifts are detected in the active Zürich classes, and are one order of magnitude larger than the linear drift.