Bifrost spectral inversions: Fast non-LTE solar chromospheric diagnostics from 3D simulations
Abstract
Modern solar observatories produce vast amounts of detailed spectral data. To infer atmospheric parameters from these data, in particular for the solar chromosphere, requires immense computational resources. This problem is becoming more acute as spatial resolution improves, and faster methods are much needed to make sense of the data. Archive-based inversions provide a cost-effective way to infer atmospheric parameters from solar spectra; they involve building databases of synthetic spectra and atmospheric models. We extended this idea to a k-nearest neighbour inversion with non-LTE chromospheric spectra from a 3D radiative-magnetohydrodynamic simulation. Our database consists of 150 million Ca II 8542 Å line profiles from a magnetically quiet simulation. We validated our method on a different simulation and then applied the database inversion to high-cadence observations taken with the Swedish 1-m Solar Telescope. We find excellent agreement between the observed and fitted spectra for almost the entire field of view. We recovered the chromospheric temperature and line-of-sight velocity and calculated the uncertainty in their inversions. The gas temperature has small uncertainties over a broad range of optical depths, and we recover a physically consistent solution, even beyond the line sensitivity region. Compared with the traditional inversion method, our approach is four orders of magnitude faster. Limitations and future improvements of the method are discussed.
Versions
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BibTeX
@misc{udnæs2026bifrost,
title = {{Bifrost spectral inversions: Fast non-LTE solar chromospheric diagnostics from 3D simulations}},
author = {Elias R. Udnæs and Tiago M. D. Pereira and Ignasi J. Soler Poquet and Luc Rouppe van der Voort},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2608.26629},
eprint = {2608.26629},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.26629},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Bifrost spectral inversions: Fast non-LTE solar chromospheric diagnostics from 3D simulations
AU - Elias R. Udnæs
AU - Tiago M. D. Pereira
AU - Ignasi J. Soler Poquet
AU - Luc Rouppe van der Voort
PY - 2026
DA - 2026/10/16
PB - arXiv
DO - 10.48550/arxiv.2608.26629
UR - https://arxiv.org/abs/2608.26629
AB - Modern solar observatories produce vast amounts of detailed spectral data. To infer atmospheric parameters from these data, in particular for the solar chromosphere, requires immense computational resources. This problem is becoming more acute as spatial resolution improves, and faster methods are much needed to make sense of the data. Archive-based inversions provide a cost-effective way to infer atmospheric parameters from solar spectra; they involve building databases of synthetic spectra and atmospheric models. We extended this idea to a k-nearest neighbour inversion with non-LTE chromospheric spectra from a 3D radiative-magnetohydrodynamic simulation. Our database consists of 150 million Ca II 8542 Å line profiles from a magnetically quiet simulation. We validated our method on a different simulation and then applied the database inversion to high-cadence observations taken with the Swedish 1-m Solar Telescope. We find excellent agreement between the observed and fitted spectra for almost the entire field of view. We recovered the chromospheric temperature and line-of-sight velocity and calculated the uncertainty in their inversions. The gas temperature has small uncertainties over a broad range of optical depths, and we recover a physically consistent solution, even beyond the line sensitivity region. Compared with the traditional inversion method, our approach is four orders of magnitude faster. Limitations and future improvements of the method are discussed.
ER -