The next 19th July of 2024 Matheus Aguiar Kriginsky Silva will present his PhD thesis: On the physical nature of chromospheric spicules and coronal rain.
Title: On the physical nature of chromospheric spicules and coronal rain
Author: Matheus Aguiar Kriginsky Silva
Directors: Dr. Ramón Julio Oliver Herrero
Abstract:
Our star plays host to a myriad of fascinating and astounding phenomena. Its
atmosphere, marked by the interplay between the radiation field and the magnetised
plasma, serves as an intriguing plasma physics laboratory.
The chromosphere, where the magnetic pressure and the gas pressure battle each other
for the dominance over the overall dynamics of the plasma, is filled with hair-like dense
structures. When observed near the solar limb, those features are named spicules. This
denomination becomes less homogeneous on the solar disc, where fibrillar structures
are classified less broadly into mottles, dynamic fibrils, long fibrils, and the list goes on.
Spicules, with their dynamic nature marked by their short lifetimes, the presence of
propagating waves and their abundance, can play a crucial role in the transport of mass
and energy through the solar atmosphere. Therefore, their correct modelling is a crucial
part of solar physics in general. This modelling heavily relies on observational
constraints.
Additionally, another spectacular and puzzling physical phenomenon that connects all
the different layers of the solar atmosphere is coronal rain. Coronal loops, acting as
highways for the circulation of the plasma in the solar corona, are often subjected to
inhomogenous heating sources, mainly concentrated at their footpoints. This footpoint
heating generates flows of heated plasma that rise along the magnetic field lines. Since
the radiative losses are not compensated for far away from the footpoints, the plasma
finds itself in a state of thermal non-equilibrium. This leads to a catastrophic cooling of
the material inside the coronal loop that becomes increasingly dense and cold,
eventually cooling down to chromospheric temperatures. This material will eventually
evacuate the coronal loop in the form of what is known as coronal rain. The nature of the
heating sources that lead to coromal rain are still a matter of intense research. Therefore,
additional observational information about the state of the coronal rain plasma is
necessary in order to understand this phenomenon. Additionally, coronal rain clumps,
being cold intruders in the million-degree corona, can act as coronal magnetic field
sensors.
The small size of coronal rain clumps and spicules has made it impossible for past
instruments to properly resolve them, and progress in understanding them was slow.
Over the past two decades, with a massive improvement on the spatial and temporal
resolution of instruments, a new boom on the study of these structures has started. At
the same time, advances in computational power have allowed for the once forbiddingly
time consuming task of performing inversions of spectral lines a common practice. We
aim on this thesis to benefit from both these instrumentational and computational
advances by providing more observational constraints on the nature of spicules and
coronal rain clumps through the analysis of high-resolution, high-cadence observations.
