Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh53c..03l&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SH53C-03
Astronomy and Astrophysics
Astrophysics
[7500] Solar Physics, Astrophysics, And Astronomy, [7529] Solar Physics, Astrophysics, And Astronomy / Photosphere
Scientific paper
We examine the role of the magnetic field in solar surface convection using the MURaM radiative MHD code. Using two 74x74x16 Mm simulations, one without magnetic field and one with an initially uniform and vertical 10 Gauss field, we investigate the role of magnetic field in supergranular scale selection. We find that the simulation with magnetic field has two peaks in the photospheric kinetic energy spectrum, one corresponding to granular size scales and a second peak near 24 Mm, while the purely hydrodynamic simulation has a single peak near the size scale of granulation (Figure 1). We examine two possible physical mechanisms which may underlie this increased power at low wavenumbers: the decreased opacity in magnetic elements near the photosphere which increases the radiative cooling there and the coupling, by regions of high magnetic flux density in convective downflows, of deeper larger scale motions to the photosphere. These mechanisms imply two very different processes. The first suggests that supergranulation is organized in the photosphere where radiation escapes the system (top down) and the second suggests that the large scale convection deep in the sun influences the scales observed in the photosphere (bottom up). Temporal cross correlation is used to examine which direction information is moving during pattern formation across scales. Additionally, a series of experiments were conducted to isolate individual physical effects, artificially increasing and decreasing the radiative losses in regions of strong magnetic flux, reducing the importance of magnetic tension, and constraining the box depth to understand the sensitivity of the size scales observed to the boundary conditions imposed.
Lord Jesse W.
Rast Mark P.
Rempel Matthias
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