RADIATIVE MAGNETOHYDRODYNAMIC SIMULATION OF SUNSPOT STRUCTURE

By Matthias Rempel, M. Schüssler, M. Knoelker. 2008

266 citations recorded by the source corpus.

Results of a three-dimensional MHD simulation of a sunspot with a photospheric size of about 20 Mm are presented. The simulation has been carried out with the MURaM code, which includes a realistic equation of state with partial ionization and radiative transfer along many ray directions. The largely relaxed state of the sunspot shows a division in a central dark umbral region with bright dots and a penumbra showing bright filaments of about 2–3 Mm length with central dark lanes. By a process similar to the formation of umbral dots, the penumbral filaments result from magnetoconvection in the form of upflow plumes, which become elongated by the presence of an inclined magnetic field; the upflow is deflected in the outward direction while the magnetic field is weakened and becomes almost horizontal in the upper part of the plume near the level of optical depth unity. A dark lane forms owing to the piling up of matter near the cusp-shaped top of the rising plume that leads to an upward bulging of the surfaces of constant optical depth. The simulated penumbral structure corresponds well to the observationally inferred interlocking-comb structure of the magnetic field with Evershed outflows along dark-laned filaments with nearly horizontal magnetic field and overturning perpendicular (“twisting”) motion, which are embedded in a background of stronger and less inclined field. Photospheric spectral lines are formed at the very top and somewhat above the upflow plumes, so that they do not fully sense the strong flow as well as the large field inclination and significant field strength reduction in the upper part of the plume structures.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/f28e6749ca928b1f44484495dc5cd227887ccd0c

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In Astronomy and Astrophysics

Citations in the corpus

NUMERICAL SIMULATIONS OF QUIET SUN MAGNETISM: ON THE CONTRIBUTION FROM A SMALL-SCALE DYNAMO (2014, methodology): “Rempel et al. (2009) used a different functional form of Φh = [(ur−ul)/(ui+1−ui)]2 in regions with (ur−ul) · (ui+1− ui) > 0 that suppresses, but does not completely disable diffusion for well-resolved features.”
SIMULATION OF THE FORMATION OF A SOLAR ACTIVE REGION (2010, methodology): “Together with previous models of umbral convection (Schüssler & Vögler 2006) and sunspot simulations (Heinemann et al. 2007; Rempel et al. 2009a,b) suggest that umbral dots, penumbral filaments and light bridges are all manifestations of overturning magnetoconvection.”
EXTENSION OF THE MURAM RADIATIVE MHD CODE FOR CORONAL SIMULATIONS (2016, methodology): “A similar problem was already encountered in Sunspot simulations and was avoided in photospheric simulations by simply reducing the strength of the Lorentz force (Rempel et al. 2009).”