Widespread Occurrence of Trenching Patterns in the Granulation Field: Evidence for Roll Convection?

TL;DR

This study uses a specialized image analysis algorithm to detect trenching patterns in solar granulation images, providing evidence that roll convection may be a common feature in the Sun's outer convection zone.

Contribution

It introduces a novel image processing method to identify linear and curvilinear features in solar granulation images, revealing widespread trenching patterns indicative of roll convection.

Findings

Detection of parallel ridges and trenches in granulation images

Evidence supporting the presence of roll convection in the solar convection zone

Granules as overheated blobs possibly formed by convection instabilities

Abstract

Time-averaged series of granulation images are analysed using COLIBRI, a purpose-adapted version of a code originally developed to detect straight or curvilinear features in aerospace images. The algorithm of image processing utilises a nonparametric statistical criterion that identifies a straight-line segment as a linear feature (lineament) if the photospheric brightness at a certain distance from this line is on both sides stochastically lower or higher than at the line itself. Curvilinear features can be detected as chains of lineaments, using a criterion modified in some way. Once the input parameters used by the algorithm are properly adjusted, the algorithm highlights ``ridges'' and ``trenches'' in the relief of the brightness field, drawing white and dark lanes. The most remarkable property of the trenching patterns is a nearly-universally-present parallelism of ridges and trenches. Since the material upflows are brighter than the downflows, the alternating parallel light and dark lanes should reflect the presence of roll convection in the subphotospheric layers. If the numerous images processed by us are representative, the patterns revealed suggest a widespread occurrence of roll convection in the outer solar convection zone. In particular, the roll systems could form the fine structure of larger-scale, supergranular and/or mesogranular convection flows. Granules appear to be overheated blobs of material that could develop in convection rolls due to some instabilities of roll motion.