Efficient Radiative Transfer for Dynamically Evolving Stratified Atmospheres

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Friday, August 25, 2017

Language Summary or Abstract: We present a fast multi-level and multi-atom non-LTE radiative transfer method for dynamically evolving stratified atmospheres, such as the solar atmosphere. The preconditioning method of Rybicki & Hummer (RH92) is adopted.

overall spectrum and individual line profiles image
The overall spectrum and individual line profiles are shown for the full and escape probability calculations, in the static FALC model.

But, pressed for the need of speed and stability, a “second order escape probability” scheme is implemented within the framework of the RH92 method, in which frequency- and angle- integrals are carried out analytically. While minimizing the computational work needed, this comes at the expense of numerical accuracy. The iteration scheme is local, the formal solutions for the intensities are the only non-local component. At present the methods have been coded for vertical transport, applicable to atmospheres that are highly stratified. The probabilistic method seems adequately fast, stable and sufficiently accurate for exploring dynamical interactions between the evolving MHD atmosphere and radiation using current computer hardware. Current 2- and 3- D dynamics codes do not include this interaction as consistently as the current method does. The solutions generated may ultimately serve as initial conditions for dynamical calculations including full 3-D radiative transfer.

Submitted to: ApJ

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