Dr. XIANG Nanbin from the Yunnan Observatories of the Chinese Academy of Sciences (CAS), in collaboration with Researcher ZHAO Xinhua from the State Key Laboratory of Space Weather at National Space Science Center, CAS, and Professor DENG Linhua from Yunnan Minzu University, has made significant progress in the study of radial differential rotation of solar corona. Their findings, recently published in The Astrophysical Journal, provide crucial insights into the regularity of coronal rotation varying with altitude and its temporal evolution.

The solar corona exhibits differential rotation in both radial and latitudinal directions. This complex rotation facilitates magnetic reconnection in the solar corona, thereby releasing the free energy stored in the magnetic field due to the shearing and twisting motions caused by different rotation rates at the solar surface. Understandingthis rotation is key to unraveling coronal dynamics and heating mechanisms.

However, studying coronal rotation is challenging due to the corona's optical thinness for extreme ultraviolet radiation and the lack of long-lived solar structures within the corona that can serve as rotational tracers over spatial and temporal scales. As a result, much remains unknown about coronal rotation, particularly how it varies with altitude.

Solar physicists generally believe that solar radio emissions of different frequencies originate from different altitudes in the upper solar atmosphere. The researchers conducted an in-depth study on the radial differential rotation of the solar corona and its temporal variation patterns. They utilized daily solar full-disk noon radio flux data observed by the Radio Solar Telescope Network within the frequency range of 245-8800 MHz.

The researchers found that over the past 30 years, the rotation rate of solar radio flux has increased with frequency, confirming the existence of radial differential rotation in the solar corona over a period spanning approximately three solar cycles. Furthermore, their analysis revealed how the rotation of the upper solar atmosphere varies with altitude within a specific altitude range. From the temporal evolution of the rotation period lengths of solar radio flux, the coronal rotation at different altitudes from the low corona to approximately 1.3 solar radii exhibited complex variations as the solar activity cycle progresses. However, the coronal rotation rate within this altitude range has consistently slowed down gradually with increasing altitude over the past three decades.

These findings not only advance the understanding of the rotation of the upper solar atmosphere, but are also crucial for comprehending coronal dynamics and abnormal heating.

This work was supported by the National Natural Science Foundation of China, the Strategic Priority Research Program of Chinese Academy of Sciences, the "Yunnan Revitalization Talent Support Program" Innovation Team Project, the Yunnan Fundamental Research Projects, the Sichuan Science and Technology Program, the Beijing Natural Science Foundation, and the Project Supported by the Specialized Research Fund for State Key Laboratories.

Contact:
XIANG Nanbin
Yunnan Observatories, CAS
E-mail:nanbin@ynao.ac.cn