High-resolution models of solar granulation: the two-dimensional case

• Published in: Monthly notices of the Royal Astronomical Society Vol. 380; no. 4; pp. 1335 - 1340
• Main Authors: Muthsam, H. J., Löw-Baselli, B., Obertscheider, Chr, Langer, M., Lenz, P., Kupka, F.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.10.2007; Blackwell Science; Oxford University Press
• Subjects: Astronomy; Astrophysics; convection; Earth, ocean, space; Exact sciences and technology; Sun; Sun: granulation; Turbulence; waves; convection; waves; Sun: granulation; turbulence; Turbulence; Two dimensional model; High temperature; Topology; Sun; Convection; Solar granulation; Vortices; Vorticity; Instability; Low temperature
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2007.12185.x

Using advanced numerical schemes and grid refinement, we present 2D high-resolution models of solar granulation with particular emphasis on downflowing plumes. In the high-resolution portion of our simulation, a box measuring 1.97 × 2.58 Mm2 (vertical × horizontal), the grid size is 1.82 × 2.84 km2. Calculations at the resolution usually applied in this type of simulations amount to only a few horizontal gridpoints for a downflowing plume. Due to the increased number of gridpoints in our high-resolution domain, the simulations show the development of vigorous secondary instabilities of both the plume's head and stem. The plume's head produces counterrotating vortex patches, a topology due to the 2D nature of the simulations. Below a depth of about 1 Mm, the plume's head and stem instabilities produce, in these 2D models, patches of low density, temperature, pressure and high vorticity which may last for all of our simulation time, ∼10 min, and probably considerably longer. Centrifugal forces acting in these patches counteract the strong inward pressure. Probably most importantly, the plume's instabilities give rise to acoustic pulses created predominantly down to ∼1.5 Mm. The pulses proceed laterally as well as upwards and are ubiquitous. Ultimately, most of them emerge into the photosphere. A considerable part of the photospheric ‘turbulence’ in these models is due to those pulses rather than to some sort of eddies. The upflows in granules are smooth where they reach the photosphere from below even in the present calculations; however, the pulses may enter in the photosphere also in granular upflows.