HAO Colloquium - Rebecca Centeno Elliott, HAO

Magnetic field diagnostic tools for the Solar Chromosphere

Our knowledge of the magnetic fields in the Sun's atmosphere relies, almost entirely, on our ability to interpret the intensity and the polarization of the light that it emits. Encoded in the subtleties of the polarized spectrum we can find a wealth of information about the thermodynamic and magnetic properties of the Sun's atmosphere, which, in turn, are key to understanding the drivers of Space Weather and to eventually enabling accurate forecasts. Sitting between the dynamically driven Photosphere and the magnetically dominated Corona, the solar Chromosphere harbors the key to quantifying the state and the evolution of the Sun's outer magnetic envelope.

In this talk I will review the accuracy of different magnetic field diagnostic tools applied to the chromospheric spectral line of Ca II at 8542 Angstroms. This line is the most popular probe for inferences of the chromospheric magnetism, yet the physical processes responsible for its polarization signals are not fully captured by existing spectral line interpretation methods.

First I will assess the validity of the weak field approximation, a vastly simplifying yet robust assumption that provides a fast method for qualitative estimates of the magnetic field vector. Then, I will address the limitations of interpreting the observations of this calcium line using existing spectral line inversion codes that do not account for the physics of scattering polarization and the Hanle effect. Lastly, I will report on some work in progress to map the polarization spectrum to the Sun's physical state using machine-learning techniques, in an effort to develop a computationally affordable method to interpret these complex polarization signals and quantify the magnetic fields behind them.

Date and time: 
Wednesday, February 17, 2021 - 2:00pm to 3:00pm