Height-dependent differential rotation of the solar atmosphere determined by the CHASE spectroscopic observation

Abstract

Rotation is an intrinsic property of the stars including the Sun. Studying how stars rotate is essential for modeling their structure, formation and evolution [1, 2], and understanding their interaction with interplanetary environment [3, 4]. The Sun is a unique candidate that we can observe in detail and explore its rotation from the interior to the atmosphere [5, 6]. To date, we still do not know exactly how the Sun rotate depending on the latitude and altitude. The Chinese Hα Solar Explorer (CHASE) [7], the first space-based solar telescope of China, answers the question to a certain extent. The CHASE mission provides seeing-free spectroscopic observations of the whole solar disk at the wavebands of Si I (6560.58 Å), Fe I (6569.21 Å), and Hα (6562.81 Å) with a very high spectral resolution, which facilitates us to derive simultaneously the precise photospheric and chromospheric Dopplergrams [8]. It is found that the Sun rotates faster at higher surface layers from the photosphere to the chromosphere. The equatorial rotation rate is calculated to be 2.79 ± 0.01 μrad s−1 at the bottom of the photosphere, 2.83 ± 0.01 μrad s−1 at the middle photosphere, and 3.07 ± 0.02 μrad s−1 at the upper chromosphere. The ubiquitous frozen-in-plasma magnetic field probably plays the key role in producing the abnormal rotation rates of the solar atmosphere. The results have important implications for the solar dynamo processes and solar atmospheric heating problems.