Rotational periodicities in sunspot relative numbers

Balthasar, H.

doi:10.1051/0004-6361:20077475

Cited by 25 publications

(17 citation statements)

References 39 publications

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“…This contradicts the result of Heristchi & Mouradian (2009), who found no north-south asymmetry in solar rotation. Large B values for both hemispheres strongly suggest that sunspot groups follow the differential rotation law, which differs from the conclusion of Balthasar (2007).…”

Section: Discussioncontrasting

confidence: 57%

“…However, lifetimes and rotation velocities of active longitudes obtained for different tracers of solar activity have been found to vary significantly. Balthasar (2007) noted, by analyzing sunspot numbers , that the rotation period varies over long timescales. Heristchi & Mouradian (2009) found an increase in the rotation rate from cycle 19 to cycle 23 by calculating sunspot numbers and the coronal radio flux at 10.7 cm.…”

Section: Introductionmentioning

confidence: 99%

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Global analysis of active longitudes of sunspots

Zhang

Мурсула

Usoskin

et al. 2011

A&A

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Context. Active longitudes have been found in various manifestations of solar activity. The longitudinal distribution of, e.g., sunspots and solar X-ray flares shows two persistent preferred longitudes separated by roughly 180 degrees. We previously studied solar X-ray flares using an improved version of a dynamic, differentially rotating coordinate system and found enhanced rotational asymmetry and rotation parameter values that are consistent for the three classes of X-ray flares. Aims. We aim to find the optimal values of rotation parameters of active longitudes of sunspots for several different time intervals and separately for the two solar hemispheres. Methods. We perform a global study of the longitudinal location of sunspots (all sunspots and first appearance sunspots) using a refined version of a dynamic, differentially rotating coordinate system. Results. We find that the rotation parameters for sunspots are in good agreement with those obtained for X-ray flares using the same method. The improved method typically finds somewhat faster equatorial rotation with better accuracy. The improved treatment also leads to a larger non-axisymmetry. Rotation parameters for all sunspots and first appearances closely agree with each other, but nonaxisymmetry is systematically larger for all sunspots than for first appearances, suggesting that strong fields follow more closely the pattern of active longitudes. The refined method emphasizes hemispheric differences in rotation. Over the whole interval, the mean rotation in the southern hemisphere is slower than in the north. We also find significant temporal variability in the two rotation parameters over the 136-year interval. Interestingly, the long-term variations (trends and residual oscillations) in solar rotation are roughly the opposite in the northern and southern hemispheres. Conclusions. Rotation parameters vary differently with time in the northern and southern hemispheres. Both sunspots and flares strongly suggest that the northern hemisphere rotated considerably faster but the southern hemisphere slightly slower than the Carrington rotation rate during the last three solar cycles.

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Section: Discussioncontrasting

confidence: 57%

Section: Introductionmentioning

confidence: 99%

Global analysis of active longitudes of sunspots

Zhang

Мурсула

Usoskin

et al. 2011

A&A

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“…In that paper also the power spectrum of the rotation velocity residuals for the years 1878-1981 was analysed and the periods of 32.6, 10.6, 5.2, and 3.5 years were identified. It is interesting to note that a period of about 5 years in sunspot relative numbers was also found by Balthasar (2007), while a period of the "flip-flop" oscillation in sunspot activity of about 3.7 years was reported by Berdyugina & Usoskin (2003).…”

Section: The Data Sets and Reduction Methodsmentioning

confidence: 87%

On the solar rotation and activity

Brajša¹,

Wöhl

Ruždjak

et al. 2007

Astron Nachr

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Thei nteractionb etween differentialr otationa nd magnetic fieldsi nthe solar convectionz one wasr ecently modelledb y Brun ( 2004). Onec onsequence of that model is that theM axwells tresses can oppose theR eynolds stresses, and thus contribute to thet ransport of thea ngular momentum towards thes olar poles, leading to ar educed differentialr otation. So,when magnetic fieldsare weaker,amore pronounced differentialrotationcan be expected, yielding ahigher rotation velocity at lowlatitudes takenonthe average. This hypothesisisconsistent with thebehaviour of thesolar rotationduring theM aunder minimum. In this work we search for similars ignatures of ther elationshipb etween thes olar activity and rotationd etermined tracing sunspot groups and coronal bright points. We use thee xtended Greenwich datas et and as eries of full-discs olar images takena t2 8.4n mw ith theE IT instrument on theS OHO spacecraft (1998)(1999)(2000). We investigatethe dependence of thesolar rotationonthe solar activity (describedbythe relative sunspot number) andthe interplanetary magnetic field (calculatedfromthe interdiurnal variability index).Possible rotationalsignatures of twoweak solar activity cycles at thebeginning of the20thcentury (Gleissbergminimum) are discussed. The interaction between differential rotation and magnetic fields in the solar convection zone was recently modelled by Brun (2004). One consequence of that model is that the Maxwell stresses can oppose the Reynolds stresses, and thus contribute to the transport of the angular momentum towards the solar poles, leading to a reduced differential rotation. So, when magnetic fields are weaker, a more pronounced differential rotation can be expected, yielding a higher rotation velocity at low latitudes taken on the average. This hypothesis is consistent with the behaviour of the solar rotation during the Maunder minimum. In this work we search for similar signatures of the relationship between the solar activity and rotation determined tracing sunspot groups and coronal bright points. We use the extended Greenwich data set and a series of full-disc solar images taken at 28.4 nm with the EIT instrument on the SOHO spacecraft (1998)(1999)(2000). We investigate the dependence of the solar rotation on the solar activity (described by the relative sunspot number) and the interplanetary magnetic field (calculated from the interdiurnal variability index). Possible rotational signatures of two weak solar activity cycles at the beginning of the 20th century (Gleissberg minimum) are discussed.

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“…Discrepancies for the same tracers (for various authors) may be due to the time intervals and lengths of data included. Increasing evidence (Balthasar et al 1986;Bai 2003;Brajša et al 2006Brajša et al , 2007Balthasar 2007;Heristchi & Mouradian 2009) suggests that the solar differential rotation changes from cycle to cycle and even within one cycle. Bouwer (1992) claimed that precise rotation periods between 27 and 28 days persist only for a short time, sometimes only for a few solar rotations.…”

Section: Introductionmentioning

confidence: 99%

Consistent long-term variation in the hemispheric asymmetry of solar rotation

Zhang

Мурсула

Usoskin

2013

A&A

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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.

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Rotational periodicities in sunspot relative numbers

Cited by 25 publications

References 39 publications

Global analysis of active longitudes of sunspots

Global analysis of active longitudes of sunspots

On the solar rotation and activity

Consistent long-term variation in the hemispheric asymmetry of solar rotation

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