Modeling and diagnosing the solar atmosphere - from NLTE radiative transfer to spectropolarimetric inversions

by Dimitri Arramy (Stockholm University)

Wednesday 21 Oct 2026, 13:30 → 14:30 Europe/Stockholm

FC 61 (AlbaNova Main Building)

Spectropolarimetric observations provide a powerful means of investigating the physical conditions and magnetic structure of the solar atmosphere. However, interpreting these observations remains challenging, particularly in the chromosphere, where the interaction between radiation and matter is inherently non-local and departures from local thermodynamic equilibrium (NLTE) become essential. Reliable atmospheric diagnostics therefore depend not only on the quality of the observations, but also on the numerical methods and physical assumptions underlying their interpretation.

In this talk, I will discuss recent efforts to address some of these challenges, from developing alternative numerical methods for solving the NLTE radiative transfer problem to investigating the interpretation of magnetic field changes during solar flares. In particular, I will show how variations in spectral line formation can complicate the interpretation of rapid magnetic field evolution inferred from chromospheric observations. Finally, I will discuss ongoing developments aimed at incorporating coronal irradiation into radiative transfer calculations, with applications to the formation and diagnostic potential of helium spectral lines.

Together, these studies illustrate how advances in numerical modeling and a better understanding of spectral line formation can help improve our ability to diagnose the dynamic solar atmosphere.