Differential Rotation of Recurrent Sunspots in Solar Cycles 23–25

다국어 초록 (Multilingual Abstract)

In this study, we explore the solar differential rotation using recurrent sunspots observed by space-borne instruments from August 1996 to June 2025. To avoid systematic errors, the differential rotation profiles are calculated taking into account both Earth’s elliptical orbit and the inclination of the solar rotation axis to the ecliptic. We have found that the equatorial rotation rate first increases and then decreases in Solar Cycles 23, 24, and 25, which can be interpreted as torsional oscillations with a period of approximately 11 years. When comparing the angular rotation rates at the solar maximum and minimum, the latitudinal gradient of rotations at solar minima exhibits significant cycle-to-cycle variation. During the descending phase, the latitudinal gradient of rotations changes significantly between solar cycles. The latitudinal gradient of rotations in the northern hemisphere is comparable across solar cycles, whereas that in the southern hemisphere displays significant modulations across solar cycles. In terms of the Zürich sunspot classification system, the equatorial rotation rate is higher and the differential rotation is stronger for J-type groups than for H-type groups. It is also attempted to investigate the dependence on the order of successive passages, revealing that although the equatorial rotation rates for the first and second passages are similar, the differential rotation for the second passage appears significant. This is indicative of less rigid rotation during the second passage. To conclude, we point out that the Sun appears to rotate more differentially in the case that the solar magnetic activity is relatively weaker, when comparing cases of weak and strong solar activity.