Consistent long-term variation in the hemispheric asymmetry of solar rotation
Abstract
Context. Solar active longitudes and their rotation have been studied for a long time using various forms of solar activity. However, the results on the long-term evolution of rotation rates and the hemispheric asymmetry obtained by earlier authors differ significantly from each other.
Aims: We aim to find a consistent result on the long-term migration of active longitudes of sunspots in 1877-2008 separately for the two hemispheres.
Methods: We used a dynamic, differentially rotating reference system to determine the best-fit values of the differential rotation parameters of active longitudes for each year in 1877-2008. With these parameters we determined the momentary rotation rates at the reference latitude of 17° and calculated the non-axisymmetries of active longitudes. We repeated this with five different fit intervals and two weighting methods and compared the results.
Results: The evolution of solar surface rotation in each hemisphere suggests a quasi-periodicity of about 80-90 years. The long-term variations of solar rotation in the northern and southern hemisphere have a close anti-correlation, leading to a significant 80-90-year quasi-periodicity in the north-south asymmetry of solar rotation. The north-south asymmetry of solar rotation is found to have an inverse relationship with the area of large sunspots. The latitudinal contrast of differential rotation is also found to be anti-correlated with the sunspot area. Different fit and weight methods yield similar results.
Conclusions: Our results give strong evidence for the anti-correlation of the rotation of the two solar hemispheres. The long-term oscillation of solar rotation suggests that a systematic interchange of angular momentum takes place between the two hemispheres at a period of about 80-90 years.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- April 2013
- DOI:
- 10.1051/0004-6361/201220693
- Bibcode:
- 2013A&A...552A..84Z
- Keywords:
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- Sun: activity;
- Sun: rotation;
- sunspots