Multidimensional Radiation Hydrodynamics
We describe a time-dependent, multidimensional radiation-hydrodynamic problem for the H line of Ca II in the solar chromosphere and propose an empirical approach using time-independent, one-dimensional equations. The purpose of the investigation is to determine the salient features of the structure of the underlying atmosphere and to decide between two fundamentally different models of the chromosphere. We discuss the case of the oscillations of the small-scale calcium bright points in the quiet chromosphere, whose intensities fluctuate intermittently with periods near the acoustic cutoff period of 3 min. The observed profile of the H line shows that a bright point is formed by an acoustic wave traveling upward in downward-streaming gas. The shape of the oscillating gas is approximately that of a cone oriented vertically, with the apex in the photosphere and an opening angle of ∼90°. The effects of multidimensional radiative transfer on the solution of the equations of radiation hydrodynamics are likely to be small compared with the effects on 3D wave propagation, and the influence on the emergent radiation field may be treated in a perturbation approach.
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