Morphological variations of solar granules in the presence of magnetic fields

Solar granulation consists of dynamic convective plasma cells that rise from the solar interior to the surface. The interaction between this plasma cells and the Sun’s magnetic field provides valuable insights into the dynamics of plasma near the solar surface and how it changes in the presence of magnetic field. This study aims to analyse the morphological characteristics of solar convective cells, investigating the relationship between magnetic field properties and granule dynamics. In particular, we examine how granule properties, such as area, shape, and brightness, vary under different magnetic field conditions. This research used observations of the active region NOAA 11768 taken by the Swedish 1-m Solar Telescope (SST). We applied the segmentation algorithm on the continuum intensity images to identify individual granules and determine their sizes, shapes, and mean brightness. We determined the magnetic field vector and line-of-sight velocity from the CRISP spectropolarimetric data to investigate the role of these parameters on the properties of granules. We found that granule area decreases systematically with increasing magnetic field strength, with the largest granules found in non-magnetic regions and a mean granule area of approximately 1.58 arcsec2 with an effective diameter of 1.42 arcseconds. Both mean continuum intensity and granule size decrease with stronger magnetic fields, demonstrating the suppression of convective energy transport in magnetised regions. However, we do not find any correlation between the mean brightness of granules and mean up-flow velocity within the granules. We observe highly elongated granules in both magnetic and non-magnetic regions, but close to circular granules are observed only in non-magnetic areas. We find indications of alignment between the major axis of granules and magnetic field azimuth in regions with a strong horizontal component of the magnetic field. These findings confirm that granules are highly sensitive to the presence of magnetic fields, with strong fields inhibiting lateral expansion of convective cells.