Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Magneto-convection in a sunspot umbra   Results from a realistic simulation of 3D radiative magneto-convection 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
cusp-like 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.

3
The categories of this paper are: physics
24
The categories of this paper are: dg-ga
10
The categories of this paper are: q-bio
29
The categories of this paper are: funct-an
13
The categories of this paper are: quant-ph
2
The categories of this paper are: math
16
The categories of this paper are: stat
7
The categories of this paper are: hep-th
23
The categories of this paper are: solv-int
4
The categories of this paper are: cond-mat
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The categories of this paper are: comp-gas
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The categories of this paper are: bayes-an
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The categories of this paper are: mtrl-th
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The categories of this paper are: gr-qc
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The categories of this paper are: math-ph
33
The categories of this paper are: plasm-ph