HAO Colloquium - Dana Lacatus, HAO

Spectroscopic Investigation of the Solar Atmosphere

The solar chromosphere plays a critical role in most of the open questions of solar physics, from coronal heating to the acceleration of the solar wind. It spans only 2000 km, but nine pressure scale heights, while the temperature increases by some two orders of magnitude. This layer is the location of most of the solar radiative losses, with the emission dominated by singly ionized ions. Despite its modest dimensions, the plasma properties make interpretation challenging, because most lines originating here are optically thick and formed in non-LTE.

We present an exploration of the chromospheric emission, from quiet to flaring solar conditions, using spectroscopic data from the IRIS instrument. The main focus of this study is the variability of the Mg II resonance lines, investigating how their profiles change based on the emitting solar structure. The extraction of the different spectral features from the observed emission profile is detailed and general trends are discussed.

Using quiet sun datasets we investigate potential characteristics that provide better contrast for distinguishing Coronal Holes from quiet sun in chromospheric emission. Thus we explore if any profile feature is more sensitive to the slightly different magnetic morphology, given that coronal holes are dominated by open field lines contributing to the solar wind acceleration.

We also explore the enhanced emission and wide variation of profiles in more active conditions leading up, during, and after a strong solar flare. For a complete picture of the flaring event, we also include information covering the surrounding solar atmosphere, using data from IRIS, SDO, and RHESSI. The slow rise and eventual destabilization of a filament is found to be preceding the flare. In the descending phase of the flare, we identified an extended coronal rain episode that persisted for more than an hour and was characterized by peculiarly wide profiles in both chromospheric and TR emission lines.

Date and time: 
Wednesday, November 13, 2019 - 2:00pm to 3:00pm