Periodicity in the Rotation of the Solar Transition Region and Sunspot Numbers

Abstract

The long-term study of the temporal variation of the rotation period of the solar photosphere, chromosphere, and corona has been widely undertaken. To date it is unclear whether the temporal variation of the rotation period of the solar transition region has a systematic periodicity. In this article we perform a study on the temporal variation of the rotation period of the solar transition region. For this purpose, we use the Lyman \(\alpha \) line emission at a wavelength of 121.56 nm corresponding to the solar transition region from the year 1965 to 2019, covering four complete solar cycles (i.e., Cycles 21, 22, 23, 24) as well as descending and ascending phases of Cycles 20 and 25, respectively. An autocorrelation analysis depicts that the average sidereal rotation period of the transition region (from 1965 to 2019) is 24.8 days. Furthermore, we find that a significant periodicity of about 12 years exists in the temporal variation of the sidereal rotation period of the solar transition region. The results indicate that this periodicity is closely linked to the 11-year Schwabe cycle. A cross-correlation analysis between the time series of the sidereal rotation period and sunspot numbers (as a function of lag in years) exhibits a positive correlation between these aforementioned parameters. From this result, we can state that the sidereal rotation period of the solar transition region leads the solar activity by about six months. This correlation again proves the periodicity of about 11 years in the rotation period of the transition region which is closely linked to the 11-year Schwabe cycle. Furthermore, long-term variation of rotation periods also demonstrates a decreasing trend from 1965 to 2019, which is similar to that in the sunspot numbers. From this long-term study, it seems that solar activity is largely driven by solar rotation.