Small-scale dynamics and large-scale stability of the outer solar atmosphere
by Jamie Gorman
Date of Examination:2024-05-29
Date of issue:2025-04-14
Advisor:Prof. Dr. Hardi Peter
Referee:Prof. Dr. Stefan Dreizler
Referee:Prof. Dr. Wolfram Kollatschny
Referee:Prof. Dr. Ansgar Reiners
Referee:Prof. Dr. Arnulf Quadt
Referee:Dr. Lakshmi Pradeep Chitta
Persistent Address:
http://dx.doi.org/10.53846/goediss-11113
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Abstract
English
The Sun has long been utilized as an observatory for gaining a better understanding of high-energy plasma physics. With the advent of the space age and the continual improvement of Sun-observing instruments, physicists have gained even greater ability to see the finer details within the solar atmosphere. This has only led to more questions about how the physics of the Sun plays out. One of the greatest questions in solar atmospheric physics has been in regards to coronal heating and the transfer of energy outward from the solar surface. Understanding the small-scale processes that are the primary components of coronal heating has become crucial for an understanding of the ultimate behavior of the solar wind. This also opens our eyes to which physical processes are actually relevant for sustained heating, and thereby the production and sustainability, of the corona. This thesis analyzes commonplace features of the solar atmosphere in order to understand and investigate energy transfer in the outer layers of the solar atmosphere. The first work included in this thesis presents a case study of a transition region network jet. These small-scale jets are known to be highly prevalent across the solar disk and are proposed to be significant contributors to the solar wind, thereby aiding in the energy transfer through the corona. The analysis of the jet reveals multiple plasma flow components emanating from a small region of strong, mostly single-polarity magnetic field concentration. The mass flows associated with the jet, as determined from the spectral profiles of Mg II and Si IV, suggest that the jet is initiated and launched in the upper chromosphere, perhaps by magnetic reconnection, and then reaches the transition region. Although traces of the jet are not seen in the hotter coronal channels available for this observation, the energy associated with this single event matches what is required to power the solar wind, further supporting the hypothesis that such small-scale jet events are important components in coronal heating models. The second work follows this notion up by inspecting the quiet solar corona as imaged in the extreme ultraviolet channel of the High Resolution Imager on board Solar Orbiter. While nanoflare heating and other models of coronal heating that consider a large number of discrete events (such as jets) would suggest a large number of detectable brightenings in the quiet Sun when imaged at high resolution and cadence, such as provided by this observation, no such outcome is observed. Instead, the scene appears steady and diffuse across supergranular-sized portions of the observation that make up most of the field of view. These areas of diffuse corona lack the evident structuring and highly variable intensity fluctuations that are seen in coronal bright points and loop-like regions of the observation, despite having comparable overall intensity counts. The general diffuse nature of the observation is also significant in that it lasts for the entire 25 min observing period, raising the question of which processes could sustain such an observable phenomenon. This ultimately provides an important constriction to the heating processes of the corona, since the diffuse regions are such a dominant portion of the quiet coronal emission and therefore total coronal energy budget.
Keywords: Sun: atmosphere; Sun: corona; Sun: UV radiation; Astrophysics - Solar and Stellar Astrophysics; Sun: chromosphere; Sun: transition region; line: profiles
