Comparison of the sidereal angular velocity of subphotospheric layers and small bright coronal structures during the declining phase of solar cycle 23

Context. We compare solar differential rotation of subphotospheric layers derived from l ocal helioseismology analysis of GONG++ dopplergrams and the one derived from tracing small bright coronal structures (SBCS) using EIT/SOHO images for the period August 2001 ‐ December 2006, which correspond to the declining phase of solar cycle 23. Aims. The study aims to find a relationship between the rotation of t he SBCS and the subphotospheric angular velocity. The northsouth asymmetries of both rotation velocity measurements are also investigated. Methods. Subphotospheric differential rotation was derived using ring-diagram analysis of GONG++ full-disk dopplergrams of 1 min cadence. The coronal rotation was derived by using an automatic method to identify and track the small bright coronal str uctures in EIT full-disk images of 6 hours cadence. Results. We find that the SBCS rotate faster than the considered upper s ubphotospheric layer (3Mm) by about 0.5 deg/day at the equator. This result joins the results of several other magn etic features (sunspots, plages, faculae, etc.) with a high er rotation than the solar plasma. The rotation rate latitudinal gradients of th e SBCS and the subphotospheric layers are very similar. The SBCS motion shows an acceleration of about 0.005 ◦ day −1 /month during the declining phase of solar cycle 23, whereas the angular velocity of subsurface layers does not display any evident variation with time, except for the well known torsional oscillation pat tern. Finally, both subphotospheric and coronal rotations of the southern hemisphere are predominantly larger than those of the northern hemisphere. At latitudes where the north-south asymmetry of the angular velocity increases (decreases) with activity for the SBCS, it decreases (increases) for subphotospheric layers.