Dynamic Coupling of the Solar Atmosphere: Instrumentation and Observations

Ghosh, Avyarthana (2019) Dynamic Coupling of the Solar Atmosphere: Instrumentation and Observations. PhD thesis, Indian Institute Of Science Education and Research, Kolkata.

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Abstract

The persistent sources of energy and mass in the solar atmosphere, overcoming the radiative loss and mass loss (due to solar wind and Coronal Mass Ejections) respectively are questions which scientists are working on for decades. This is imperative to understand for improving our knowledge of high energy physics, atomic physics, plasma physics, MHD and turbulence as well as the scenario in other stellar atmospheres. This thesis uses imaging and spectroscopic observa- tions spanning a wide range of the electromagnetic spectrum to answer some of these questions. The thesis consists of two parts. In the first part, we have studied the observations recorded from currently existing space missions. The second part is dedicated to the designing of few optical components and end-to- end performance modelling of the Solar Ultraviolet Imaging Telescope (SUIT) that will fly on-board Aditya-L1 satellite. It is the maiden endeavour of the In- dian Space Research Organisation (ISRO), solely dedicated to solar observations from the Sun-Earth Lagrangian-1 (L1) point. A comprehensive understanding of plasma dynamics in different types of fea- tures, seen in different layers of the solar atmosphere, is the key to unravelling the physical conditions and processes that are involved in their formation, evo- lution and sustenance. Some of these features are concentrated over smaller regions with strong and more dynamically evolving magnetic field lines (Active Regions, AR) while others are more ubiquitous with less dynamic and weaker field lines (Quiet Sun, QS). In this thesis, we have studied the granules, typically the QS features, on the photosphere using the very high spatial resolution obser- vations recorded with IMaX on-board the SUNRISE balloon-borne observatory. Simultaneously, a significant amount of effort has been put to observations and analysis of the ARs and loops using several state-of-the-art spectroscopic and imaging instruments. The spectroscopic observations from the Interface Region Imaging Spectrometer (IRIS) and the Extreme-UV and Imaging Spectrometer (EIS) aboard the Hinode are used for deriving the plasma parameters in ARs as well as other associated structures. Whereas, the imaging facilities viz., the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) on-board the Solar Dynamics Observatory (SDO) are used for studying the formation and evolution. Together, these lead to a holistic view of the physical conditions and energy in the solar atmosphere as well as the transfer of mass and energy amongst different layers. The solar atmospheric heating is a convoluted scenario of acoustic heating and magnetic heating. While magnetic heating is predominant in the upper solar atmosphere and could be, to some extent, be explained by the above studies, a considerable amount of work is pending for the acoustic heating scenario which is the major driving factor in lower solar atmosphere. The SUIT payload onboard Aditya-L1 mission will observe the Sun between 2000–4000 Å and provide observations of photosphere to upper chromosphere using 11 different bandpass filters. These filters will slice very intricately through the lower solar atmosphere at different heights to complete the picture of acoustic energy deposition, which is the primary agent for heating in the photosphere and chromosphere. Hence, the SUIT filters will provide excellent window to unravel the coupling among these layers in great details. We note that full disk of the Sun has never been imaged in this wavelength domain of the solar spectrum. The second part of this thesis is dedicated to the designing of a few optical components of SUIT and its end-to-end photometric as well as imaging performance modelling. The SUIT instrument combined with existing and upcoming space-based as well as ground-based instruments such as Solar Dynamics Observatory, Solar Orbiter, the Daniel K. Inouye Solar Telescope (DKIST), the Multi-Application Solar Telescope (MAST) and the future National Large Solar Telescope (NLST) will provide a comprehensive view of the solar atmosphere that has been missing.

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