Prof. DENG Linhua from Yunnan Observatories of Chinese Academy of Sciences(CAS) with collaborators (Prof. ZHENG Sheng, Associate Prof. from Center for Astronomy and Space Sciences, China Three Gorges University) investigated the rotational characteristics of the solar transition region. The 304 Å wavelength images derived from the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) between 2011 and 2022 were used in the work. This work was published in The Astrophysical Journal.

The solar rotation is very complex, with different layers of the solar atmosphere rotating at different rates. Solar differential rotation is an essential basis for the theory of solar dynamo because it plays a key role in the transformation of the solar magnetic field. The solar transition region is a thin layer between the chromosphere and corona, which has a wide range of temperature and has a strong connection with the coronal heating mechanisms. The solar photosphere, chromosphere, and corona have been paid more attention, but the rotation properties of the solar transition region are still unknown.

In this work, WU et al. used the solar full-disk images at a wavelength of 304 Å observed from the SDO/AIA to investigate the rotation of the solar transition region, and the flux modulation method was applied to their research. The 304 Å images contain information about the long-lived structure of the solar transition region, and they obtained the yearly extreme ultraviolet flux time series for different latitudes by dividing the latitudinal rectangular bands. However, the flux series needs to be detrended and high-frequency noise removed to generate the obvious periodic information through autocorrelation analysis.

It is found that the solar transition region rotates differentially, and the rotation coefficients A and B are 14.39 (±0.08) and -1.61 (±0.15), respectively. However, no prominent asymmetry in the average rotation rate of the northern and southern hemispheres was found. The researchers also found that the solar transition region rotates fastest during the solar cycle maximum, and the average rotation rate follows the overall trend of solar activity. Both the equatorial rotation rate and the latitudinal gradient of the solar transition region are smaller than that of the solar chromosphere and the corona, indicating that the solar transition region rotates more slowly and more rigidly than the other two layers. Therefore, the researchers speculated that the solar chromosphere and corona seem to restrain the rotation of the solar transition region at the same time.