Differential rotation of the solar transition region from STEREO/EUVI 30.4-nm images

Abstract

ABSTRACT The solar photosphere, chromosphere, and corona are known to rotate differentially as a function of latitude. To date, it is unclear whether the solar transition region also rotates differentially. In this work, we investigate the differential rotational profile of the solar transition region as a function of latitude, using solar full-disc (SFD) images at 30.4-nm wavelength recorded by the Extreme Ultraviolet Imager (EUVI) on board the Solar Terrestrial Relations Observatory(STEREO) space mission for the period from 2008–2018 (Solar Cycle 24). Our investigations show that the solar transition region rotates differentially. The sidereal rotation rate obtained in the ${\pm}5{^\circ }$ equatorial band is quite high (∼14.7 deg day−1), dropping to ∼13.6 deg day−1 towards both polar regions. We also find that rotational differentiality is low during the period of high solar activity (the rotation rate varies from 14.86–14.27 deg day−1), while it increases during the ascending and descending phases of the 24th solar cycle (the rotation rate varies from 14.56 to ∼13.56 deg day−1 in 2008 and 14.6–13.1 deg day−1 in 2018). The average sidereal rotation rate (over SFD) follows the trend of solar activity (maximum ∼14.97 deg day−1 during the peak phase of solar activity, slowly decreasing to a minimum ∼13.9 deg day−1 during ascending and descending phases of the 24th solar cycle). We also observe that the solar transition region rotates less differentially than the corona.