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 (CST) 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 dataset 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.
Highlights
The dynamics of the solar surface is still a main subject of research in solar physics
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
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
Summary
The dynamics of the solar surface is still a main subject of research in solar physics. The horizontally moving loops impinge on an open funnel that is located at the supergranular cell boundary. This collision may trigger magnetic reconnection, which forms the nascent solar wind. The CST method allows determining plasma flows from scales as small as 2.5 Mm (Rieutord et al 2001) up to almost the full disc (to be precise, up to 0.8 radius) of the Sun. Here we take advantage of the high spatial and temporal resolution of SDO/HMI continuum observations and use the granulation as tracers for direct measurements of the plasma flow. The paper is organised in the following way: in Sect.
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