Structure and evolution of solar supergranulation using SDO/HMI data

TL;DR

This study uses SDO/HMI data and a new tracking method to analyze the structure, evolution, and flow patterns of solar supergranulation, confirming their role as tracers of large-scale solar surface flows.

Contribution

It introduces an improved coherent structure tracking method to measure supergranulation properties and their relation to solar surface flows using high-resolution data.

Findings

Supergranules have an average lifetime of 1.5 days and a diameter of 25 Mm.

Detected differential rotation and poleward meridional flow in supergranules.

Weaker diverging flows are observed in regions with magnetic fields.

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.