Talare: Johan Bjoergen

Titel: The synthetic chromosphere

Sammanfattning:

The solar chromosphere is a dynamic layer between the photosphere and
corona. Only few and complex spectral lines can probe the chromosphere
making its observations a real challenge. To gain insight into the
chromospheric physical conditions, we can compare the observations with
3D radiation-magnetohydrodynamic models combined with forward modeling
(radiative transfer). The chromospheric environment is strongly
influenced by departures from local thermodynamic equilibrium (non-LTE),
horizontal radiative transfer (3D effects), and partially-coherent
scattering of photons (partial redistribution effects). All these
effects make the detailed 3D non-LTE radiative transfer very
computationally demanding. In this seminar, I will focus on the
chromospheric resonance lines Ca II H&K. Understanding their formation
is crucial to interpret the observations from the new imaging
spectrometer CHROMIS, recently installed at the Swedish 1-m Solar
Telescope. In our work, we modelled the Ca II H&K lines in 3D by using
simulations of a quiet Sun and active region containing sunspots and a
solar flare. For the quiet Sun, we investigated how the synthetic
observables of Ca II H&K lines are related to atmospheric parameters.
Aside from the theoretical interpretation of synthetic spectral lines, I
will also discuss how to solve the non-local thermodynamic equilibrium
radiative transfer problem more efficiently.