Structure and evolution of solar supergranulation using SDO/HMI data

¹ Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, 14 avenue Édouard Belin, 31400 Toulouse, France
² Astronomical Institute, Faculty of Mathematics and Physics, Charles University in Prague, V Holešovičkách 2, 18000, Prague 8, Czech Republic
³ Astronomical Institute, Academy of Sciences of the Czech Republic (v. v. i.), Fričova 298, 25165 Ondřejov, Czech Republic
⁴ LESIA, Observatoire de Paris, Section de Meudon, 92195 Meudon, France
⁵ Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
⁶ Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany

Received: 5 February 2014
Accepted: 20 June 2014

Abstract

Context. Studying the motions on the solar surface is fundamental for understanding how turbulent convection transports energy and how magnetic fields are distributed across the solar surface.

Aims. From horizontal velocity measurements all over the visible disc of the Sun and using data from the Solar Dynamics Observatory/Helioseismic and Magnetic Imager (SDO/HMI), we investigate the structure and evolution of solar supergranulation.

Methods. Horizontal velocity fields were measured by following the proper motions of solar granules using a newly developed version of the coherent structure tracking code. With this tool, maps of horizontal divergence were computed. We then segmented and identified supergranular cells and followed their histories by using spatio-temporal labelling. With this data set we derived the fundamental properties of supergranulation, including their motion.

Results. We find values of the fundamental parameters of supergranulation similar to previous studies: a mean lifetime of 1.5 days and a mean diameter of 25 Mm. The tracking of individual supergranular cells reveals the solar differential rotation and a poleward circulation trend of the meridional flow. The shape of the derived differential rotation and meridional flow does not depend on the cell size. If there is a background magnetic field, the diverging flows in supergranules are weaker.

Conclusions. This study confirms that supergranules are suitable tracers that may be used to investigate the large-scale flows of the solar convection as long as they are detectable enough on the surface.