Magnetoconvection in a Sunspot Umbra
By M. Schüssler, A. Vögler. 2006
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Results from a realistic simulation of three-dimensional radiative magnetoconvection in a strong background magnetic field corresponding to the conditions in sunspot umbrae are shown. The convective energy transport is dominated by narrow upflow plumes with adjacent downflows, which become almost field-free near the surface layers. The strong external magnetic field forces the plumes to assume a cusplike shape in their top parts, where the upflowing plasma loses its buoyancy. The resulting bright features in intensity images correspond well (in terms of brightness, size, and lifetime) to the observed umbral dots in the central parts of sunspot umbrae. Most of the simulated umbral dots have a horizontally elongated form with a central dark lane. Above the cusp, most plumes show narrow upflow jets, which are driven by the pressure of the piled-up plasma below. The large velocities and low field strengths in the plumes are effectively screened from spectroscopic observation because the surfaces of equal optical depth are locally elevated, so that spectral lines are largely formed above the cusp. Our simulations demonstrate that nearly field-free upflow plumes and umbral dots are a natural result of convection in a strong, initially monolithic magnetic field.
Subfields: Astronomy and Astrophysics
View Paper: https://www.semanticscholar.org/paper/8a775e7ef61640badfbbffb8c80da08b508acfe1
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In Astronomy and Astrophysics
Citations in the corpus
- Oscillations and Waves in Sunspots (2015, background): “…sunspot’s umbrae and penumbrae, magnetoconvection models indicate that these environments can be convective (Savage, 1969; Moore, 1973; Lee, 1993; Weiss et al., 1990; Cattaneo et al., 2003; Schüssler and Vögler, 2006; Spruit and Scharmer, 2006), see the review by Rempel and Schlichenmaier (2011).”
- CRISP Spectropolarimetric Imaging of Penumbral Fine Structure (2008, background): “The light bridge dark core ‘a’ and one of the other dark cores split up in Y-shapes at their innermost parts, similar to what was first reported by Scharmer et al. (2002) and also seen in umbral dot simulations by Schüssler & Vögler (2006).”
- Solar Surface Magnetism and Irradiance on Time Scales from Days to the 11-Year Cycle (2009, methodology): “Modelling of sunspots using current magneto-hydrodynamic codes (Schüssler and Vögler 2006) confirms that their darkness can be understood as thermal ‘plugs’ in which intense vertical magnetic fields divert heat flow from deeper layers (Spruit 1982; Foukal et al. 1983).”