Two-dimensional segmentation of small convective patterns in radiation hydrodynamics simulations

¹ Institute of Physics, IGAM, University of Graz, Universitätsplatz 5, 8010 Graz, Austria
e-mail: birgit.lemmerer@uni.graz.at
² Instituto de Astrofísica de Andalucía (CSIC), Apdo. de Correos 3004, 18080 Granada, Spain
³ Institute of Mathematics, University of Vienna, Oskar-Morgenstern-Platz 1, 1090 Wien, Austria
⁴ Indian Institute of Astrophysics, Koramangala, 560034 Bangalore, India

Received: 29 March 2013
Accepted: 6 February 2014

Abstract

Context. Recent results from high-resolution solar granulation observations indicate the existence of a population of small granular cells that are smaller than 600 km in diameter. These small convective cells strongly contribute to the total area of granules and are located in the intergranular lanes, where they form clusters and chains.

Aims. We study high-resolution radiation hydrodynamics simulations of the upper convection zone and photosphere to detect small granular cells, define their spatial alignment, and analyze their physical properties.

Methods. We developed an automated image-segmentation algorithm specifically adapted to high-resolution simulations to identify granules. The resulting segmentation masks were applied to physical quantities, such as intensity and vertical velocity profiles, provided by the simulation. A new clustering algorithm was developed to study the alignment of small granular cells.

Results. Small granules make a distinct contribution to the total area of granules and form clusters of chain-like alignments. The simulation profiles demonstrate a different nature for small granular cells because they exhibit on average lower intensities, lower horizontal velocities, and are located deeper inside of convective layers than regular granules. Their intensity distribution deviates from a normal distribution as known for larger granules, and follows a Weibull distribution.