Temporal Variations of the Solar Rotation Determined by Sunspot Groups

Abstract

The extended Greenwich data set consisting of positions of sunspot groups is used for the investigation of cycle-related variations of the solar rotation in the years 1874 -1981. Applying the residual method, which yields a single number for each year describing the average deviation from the mean value of the solar rotation, the dependence of the rotation velocity residual on the phase of the solar cycle is investigated. A secular deceleration of the solar rotation was found: the slope being statistically significant at the 3σ level. Periods of 33, 22, 11, 5.2, and 3.5 years can be identified in the power spectra. The rotation velocity residuals were averaged for all years with the same solar cycle phase relative to the nearest preceding sunspot minimum. The variation pattern reveals a higher than average rotation velocity in the minimum of activity and, to a lesser extent, also around the maximum of activity. The analysis was repeated with several changes in the reduction method, such as elimination of the secular trend, application of statistical weights, different cutoffs of the central meridian distance, division of the latitude into subregions and treating data from the years of activity minima separately. The results obtained are compared with those from the literature, and an interpretation of the observed phenomena is proposed.

A relationship between the solar rotation and activity in the period 1998–2006 analysed by tracing small bright coronal structures in SOHO-EIT images

“…This agrees with the high correlation between the rotation parameter A and various indices of solar activity. This result is consistent with many other observational findings, obtained by different tracers and methods, so a higher average rotation velocity in activity minima was found by many authors who analysed the solar rotation using various sunspot data series by different methods (Lustig 1983;Gilman & Howard 1984;Balthasar et al 1986;Hathaway & Wilson 1990;Gupta et al 1999;Khutsishvili et al 2002;Zuccarello & Zappalá 2003;Brajša et al 2006). Moreover, Chandra et al (2010) measured the differential rotation of the soft X-ray solar corona and investigated its variation with the solar activity.…”

“…For the investigation of possible variations in the solar rotation, the Greenwich data set was used by Balthasar & Wöhl (1980), Arévalo et al (1982), and Balthasar et al (1986); the Kanzelhöhe data set by Lustig (1983); the Mt. Wilson data set by Gilman & Howard (1984) and by Hathaway & Wilson (1990); the Mitaka data set by Kambry & Nishikawa (1990); the Suzuka data set by Suzuki (1998); the extended Greenwich data set by Pulkkinen & Tuominen (1998), Javaraiah (2003), Zuccarello & Zappalá (2003), Javaraiah et al (2005), Javaraiah & Ulrich (2006), and Brajša et al (2006Brajša et al ( , 2007; the Kodaikanal data set by Gupta et al (1999); and the Abastumani data set by Khutsishvili et al (2002). Also, temporal variations in the solar rotation were studied using other Article published by EDP Sciences A17, page 1 of 6…”

On the solar rotation and activity

“…Superimposed on a systematic decrease of the rotation velocity (secular deceleration) a finer modulation connected with the 11-year solar activity cycle can be seen. This type of variation was discussed in more detail by Brajša, Ruždjak & Wöhl (2006).…”

“…2 and 3 the straight lines are presented only for the case without an application of the SW procedure. The SW procedure was described in detail in the paper by Brajša et al (2006). We note that in Fig.…”

“…Further details concerning the analysis of the Greenwich data set were given in the paper by Brajša, Ruždjak & Wöhl (2006). 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.…”