From a recent study published on Monthly Notices of the Royal Astronomical Society, solar physicists know more about the systematic regularity of solar coronal rotation during the past 80 years (1939-2019). Dr. DENG Linhua, from Yunnan Observatories of Chinese Academy of Sciences, led the research.

Solar rotation is one of the essential properties of the Sun as a star, but it is still hard to understand it clearly from the existing large volume of observational data. However, the high-precision determination of solar rotation periodicity is not easy, as it depends on both the type of observational data and the analysis approach.

At present, it is widely accepted that the rotation of the solar corona could provide additional information on the construction of solar dynamo models, because it reflects the rotation characteristics in sub-photospheric layers of the Sun. Unfortunately, there is no such consensus regarding the rotation rule for features in the solar corona, the main reasons why the coronal rotation is relatively less determined are as follows: (i) there are virtually no obvious tracers, (ii) the corona is an optically thin region and (iii) it is difficult to measure the coronal magnetic field.

With the hope of adding further information on the temporal variation and underlying processes of solar coronal rotation, researches focus on the modified coronal index for nearly eight solar cycles, introduced and provided by the Slovak Central Observatory in Hurbanovo, through several time-series analysis approaches.

It is found that the coronal rotation period exhibits an obvious decreasing trend during the time interval considered, implying that the solar corona accelerates its global rotation rate in the long run. Moreover, several significant periods exist in coronal rotation, providing evidence that coronal rotation should be connected with the quasi-biennial oscillation, the 11-year solar cycle and the 22-year Hale cycle.

This work showed that sunspot activity, coronal radio flux and the green corona exhibit a similar decrease trend in rotation period over the past several decades, i.e. the Sun accelerates its global rotation rate in the long run. “However, an opposite long-term trend, namely, secular deceleration for the solar rotation rate was also obtained by some authors. To reveal the physical mechanism of the interior and surface rotation of the Sun, more studies are needed in the future.”, said Dr. DENG.

Contact:

DENG Linhua, YNAO, CAS

lhdeng@ynao.ac.cn