2018/10/31 by J. de la Cruz Rodríguez, J. Leenaarts, S. Danilovic +1 · 3 citations
Physics and Astronomy · #Chromosphere #Grid #Inversion (geology) #Ionosphere and magnetosphere dynamics #Non-equilibrium thermodynamics #Plasma #Radiative transfer #Regularization (linguistics) #Solar and Space Plasma Dynamics #Solar atmosphere #Spectral line #Standard solar model #Stellar, planetary, and galactic studies #astro-ph.IM #astro-ph.SR
paper · pdf · doi:10.1051/0004-6361/201834464
published as A&A 623, A74 (2019) · Accepted for publication in Astronomy & Astrophysics
openalex created_date 2018/10/26 · arxiv created 2019/02/01 · openalex publication_date 2019/02/02 · arxiv updated 2019/03/06 · openalex updated_date 2026/08/06
The inference of the underlying state of the plasma in the solar chromosphere remains extremely challenging because of the nonlocal character of the observed radiation and plasma conditions in this layer. Inversion methods allow us to derive a model atmosphere that can reproduce the observed spectra by undertaking several physical assumptions. The most advanced approaches involve a depth-stratified model atmosphere described by temperature, line-of-sight velocity, turbulent velocity, the three components of the magntic field vector, and gas and electron pressure. The parameters of the radiative transfer equation are computed from a solid ground of physical principles. In order to apply these techniques to spectral lines that sample the chromosphere, nonlocal thermodynamical equilibrium effects must be included in the calculations. We developed a new inversion code STiC (STockholm inversion Code) to study spectral lines that sample the upper chromosphere. The code is based on the RH forward synthesis code, which we modified to make the inversions faster and more stable. For the first time, STiC facilitates the processing of lines from multiple atoms in non-LTE, also including partial redistribution effects (PRD) in angle and frequency of scattered photons. Furthermore, we include a regularization strategy that allows for model atmospheres with a complex depth stratification, without introducing artifacts in the reconstructed physical parameters, which are usually manifested in the form of oscillatory behavior. This approach takes steps toward a node-less inversion, in which the value of the physical parameters at each grid point can be considered a free parameter. In this paper we discuss the implementation of the aforementioned techniques, the description of the model atmosphere, and the optimizations that we applied to the code. We carry out some numerical experiments to show the performance of the code and the regularization techniques that we implemented. We made STiC publicly available to the community.