Temporal Variation of Solar Coronal Rotation

Abstract

In this paper, by applying the wavelet transformation analysis to the data of the daily 10.7 cm radio flux covering the period from 1947 February 14 to 2014 August 31, a significant period of about 27 days can be found, indicating the existence of rotational modulation in the temporal variation of the daily 10.7 cm radio flux. Then, the solar coronal rotation periods are obtained based on the result of the wavelet transformation analysis, and the temporal variation of the coronal rotation is revisited. We find that there exist significant periods of about 2.1, 3.0, 4.5, 6.6, 8.6, and 10.3 yr in the temporal variation of the coronal rotation. A possible period of 22.0 yr can also be found, but its statistical significance is below the 95% confidence level. The coronal rotation seems to show a weak decreasing trend during the considered time. The dependence of the coronal rotation on solar cycle phase is analyzed. The rotation periods are found to be varying with the solar cycle phase, and they are relatively longer around the minimum year of the solar cycle. The result based on the cross-correlation analysis between the rotation periods and the daily 10.7 cm radio flux indicates that there exists a phase difference of about 5.5 yr between them.

Systematic regularity of solar coronal rotation during the time interval 1939–2019

“…It is clear from Figure 9 that the long-term decreasing trend of PLRC time series we obtained is similar to those obtained by Heristchi & Mouradian (2009), , Li et al (2012), and Xie et al (2017b). Interestingly, all of these studies used the daily 10.7 cm solar radio flux to reveal the rotational behavior of the solar corona.…”

“…Most recently. by studying the temporal variation of coronal rotation in the 10.7 cm radio flux, Xie et al (2017b) found a periodicity of 6.6 years, which was interpreted as the third harmonic of the 22-year magnetic cycle. A similar periodicity of 6.8 years was found by Xie et al (2018) who studied the equatorial rotation rate of solar magnetic fields from 1975 September to 2008 April.…”

“…That is to say, in the local wavelet power spectra shown in Figure 7, the rotation period length at a certain time point has the highest power spectrum among the periodic scales of 24-30 days, where are the length range of coronal rotation period located . Based on this conception, the rotation period length of sunspot numbers (Li et al 2011a;Xie et al 2012), sunspot areas (Li et al 2011b), solar mean magnetic field (Xie et al 2017a), and 10.7 cm solar radio flux (Xie et al 2017b) are studied and estimated. In this sense, the similar procedure could be also applied to obtain the period length of the coronal rotation (PLCR) of daily MCI at each time point during the considered time interval, and the extracted results are shown in Figure 9.…”

“…Later, Li et al (2012) also studied the cycle-related variation of coronal rotation period, and they claimed that there is no 11-year periodicity for the secular variation of rotation period length. However, Xie et al (2017b) restudied the temporal variation of coronal rotation based on the continuous wavelet transform and auto-correlation analysis, they thought that the long-term variation of coronal rotation period should be related to the 11-year Schwabe cycle, because a periodicity of 10.3 years is detected from the smoothed coronal rotation period. By studying the rotation characteristics of historical solar observations, including the Greenwich sunspot groups, the spectroscopic velocity data, the large-scale magnetic fields, and the photospheric magnetic maps, the quasi-eleven-year periodicity of solar rotation variation has also been reported by Javaraiah & Gokhale (1997), Javaraiah & Komm (1999), Obridko & Shelting (2001), Brajša et al (2006), and Xie et al (2018).…”

“…They found that there is no 11-year Schwabe cycle of statistical significance for the secular variation of rotation period length, and the solar coronal rotation does not exhibit any systematic pattern. By applying the cross-correlation analysis and wavelet transformation, Xie et al (2017b) studied the daily and monthly radio flux at 2800 MHz from 1947-2014. They found that the coronal rotation period varies with the solar cycle phase, and the rotation period is relatively longer around the minimum year of a solar cycle.…”