Abstract
Abstract Sunspot groups are often used as tracers to probe the differential rotation of the Sun. However, the results on the rotation rate variation obtained by different authors are not always in agreement. The reason for this might be a number of effects. In particular, faster decay of the following part of a sunspot group results in a false apparent shift of the area-weighted center of the group toward the leading part. In this work we analyze how significantly this effect may contribute to the derived rotation rate. For a set of 670 active regions, we compare the rotation rate derived from continuum intensity images to that derived from line-of-sight magnetograms. We found that the difference between the calculated rotation rates is 0.45° day−1 on average. This value is comparable to the difference between the rotation rate of the solar surface near the equator and at 30° latitude. We conclude that the accuracy of the rotation rate measurements using white-light images is not satisfactory. Magnetograms should be used in future research on the differential rotation of the Sun.
Highlights
The differential rotation of the Sun is an important mechanism involved in the generation of solar magnetic fields – the global dynamo process
For a set of 670 active regions, we compare the rotation rate derived from continuum intensity images to that derived from line-of-sight magnetograms
The rotation rate is usually estimated by measuring the consecutive positions of an individual sunspot or of a sunspot group observed at different times
Summary
The differential rotation of the Sun is an important mechanism involved in the generation of solar magnetic fields – the global dynamo process. The differential rotation presumably converts the poloidal global magnetic field to the toroidal one (see, e.g., a review by Charbonneau 2020). The differential rotation was observed for the first time by tracking the sunspots traversing the solar disk back in 1630s (Beck 2000). The description of the methods used to derive the differential rotation of the Sun can be found in an excellent review by Beck (2000). Sunspots are widely used as tracers to probe the solar differential rotation. The rotation rate is usually estimated by measuring the consecutive positions of an individual sunspot or of a sunspot group observed at different times. Long-term sunspot observations covering four centuries allow one to analyze the rotation rate of sunspots in detail
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