Temporal Variation of Solar Coronal Rotation

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.