Meridional motions and Reynolds stress from SDO/AIA coronal bright points data^⋆

¹ Hvar Observatory, Faculty of Geodesy, Kačićeva 26, University of Zagreb, 10000 Zagreb, Croatia
e-mail: davor.sudar@gmail.com
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
³ Astronomical Institute of the Czech Academy of Sciences, Fričova 298, 251 65 Ondřejov, Czech Republic
⁴ Department of Physics, University of Rijeka, Radmile Matejčić 2, 51000 Rijeka, Croatia

Received: 19 August 2015
Accepted: 16 December 2015

Abstract

Context. It is possible to detect and track coronal bright points (CBPs) in Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) images. A combination of high resolution and high cadence provides a wealth of data that can be used to determine velocity flows on the solar surface with very high accuracy.

Aims. We derived a very accurate solar rotation profile and investigated meridional flows, torsional oscillations, and horizontal Reynolds stress based on ≈6 months of SDO/AIA data.

Methods. We used a segmentation algorithm to detect CBPs in SDO/AIA images. We also used invariance of the solar rotation profile with central meridian distance (CMD) to determine the height of CBPs in the 19.3 nm channel.

Results. The best fit solar rotation profile is given by ω(b) = (14.4060 ± 0.0051 + (−1.662 ± 0.050)sin²b + (−2.742 ± 0.081)sin⁴b)° day^-1. The height of CBPs in the SDO/AIA 19.3 nm channel was found to be ≈6500 km. Meridional motion is predominantly poleward for all latitudes, while solar velocity residuals show signs of torsional oscillations. Horizontal Reynolds stress was found to be smaller than in similar works, but still showed transfer of angular momentum towards the solar equator.

Conclusions. Most of the results are consistent with Doppler measurements rather than tracer measurements. The fairly small calculated value of horizontal Reynolds stress might be due to the particular phase of the solar cycle. Accuracy of the calculated rotation profile indicates that it is possible to measure changes in the profile as the solar cycle evolves. Analysis of further SDO/AIA CBP data will also provide a better understanding of the temporal behaviour of the rotation velocity residuals, meridional motions, and Reynolds stress.