उदयपुर सौर वेधशाला सेमिनार

Solar active regions (ARs) are the primary sites of magnetic activity and
eruptive phenomena in the solar atmosphere. Their magnetic configuration
and complexity evolve with time and form the basis for classifying ARs into
different groups and types. Understanding how plasma properties vary
across different AR types is essential for establishing the relationship
between magnetic structure and plasma thermodynamics, as well as for
addressing fundamental questions related to magnetic reconnection, plasma
flows, and solar atmospheric heating. In this study, we plan to
investigate the thermodynamic characteristics of various transients within
ARs using spectroscopic, imaging, and magnetic field observations. By
examining different transient phenomena in ARs, we intend to establish
observational correlations between magnetic complexity and plasma
properties. This work is expected to provide insight into the role of
magnetic complexity in governing energy deposition and heating in
the solar atmosphere.

सौर रेडियो प्रेक्षण सौर कोरोना, सूर्यमंडल तथा आयनमंडल के अध्ययन के लिए महत्वपूर्ण माध्यम प्रदान करते हैं और इन्हें सौर वायुमंडल में उत्पन्न विक्षोभों का उत्कृष्ट सूचक माना जाता है। ये सौर ज्वालाओं तथा प्रभामंडलीय द्रव्यमान उत्सर्जन जैसे ऊर्जावान क्षणिक सौर घटनाओं के तात्कालिक संकेत प्रदान करते हैं।
इस व्याख्यान में, मैं सौर रेडियो प्रेक्षण का एक मूलभूत परिचय प्रस्तुत करूँगी, जिसमें रेडियो तरंगों की उत्पत्ति, उनके संचरण और अंतरग्रहीय माध्यम में उनके उत्सर्जन की प्रक्रिया को शामिल किया जाएगा।  इसके पश्चात्, मैं विभिन्न उत्सर्जन तंत्र प्रक्रियाओं एवं घनत्व मॉडलों पर चर्चा करूँगी, जो रेडियो प्रेक्षणों की व्याख्या में सहायक होते हैं। तत्पश्चात्, यह स्पष्ट किया जाएगा कि रेडियो उत्सर्जन सौर वायुमंडल में होने वाली ऊर्जावान क्षणिक घटनाओं से किस प्रकार संबद्ध होते हैं। इसके अतिरिक्त, मैं सौर रेडियो मापन के लिए प्रयुक्त विभिन्न स्पेक्ट्रोस्कोपिक एवं प्रतिबिंबन उपकरणों का परिचय दूँगी, जिनमें भू-आधारित तथा अंतरिक्ष-आधारित दोनों प्रकार के उपकरण सम्मिलित हैं। डायनेमिक स्पेक्ट्रा के माध्यम से विभिन्न प्रकार के रेडियो प्रस्फोटों  की पहचान एवं विश्लेषण किया जा सकता है, जिन्हें मुख्यतः पाँच प्रकारों (प्रकार I–V) में वर्गीकृत किया जाता है। अंततः, मैं इन घटनाओं से संबंधित अपने प्रारंभिक कार्य के परिणाम साझा करूँगी। 

The solar atmosphere is highly structured and dynamic. Observational studies of the evolution and dynamics of different structures often leads
to important results that are greatly helpful in understanding different physical processes that occur on the Sun and, thereby, addressing important questions.
This motivates for the high-resolution imaging of small-scale structures. Large telescopes are often required to achieve such high resolutions. But the
performance starts getting severely affected by the atmospheric "seeing" conditions as the apertures size increases. Thus large telescopes often
demand an adaptive optics (AO) system at their backends for the real-time compensation of the atmospheric effects. The design of an optimum AO
system often depends explicitly on the atmospheric parameters such as Fried's coherence length, r0  and coherence time. There are
different methods to estimate r0. In our work, we have chosen differential image motion (DIM) method for r0 estimation for the
observation site of MAST, 50 cm telescope, for data sets corresponding to different times in a year. There is also a low-order AO system at the back
end of the telescope which can correct up to 20 modes of aberrations. We are planning to upgrade this to a higher order AO
system with increased number of sensing and corrective elements, thereby, to further improve the resolutions. A pre-liminary design for the same has also been worked out.

Polar coronal holes are the source regions of the fast solar wind and show diverse small-scale activity. Among these, jets are transient plasma ejections frequently observed in EUV and X-ray data. Studying
their kinematics and morphology is vital for identifying the physical processes that drive them and assessing their possible role in heating the corona Polar radio brightenings, detected at microwave wavelengths and sometimes 
lacking EUV counterparts, are another prominent feature of the polar regions. Their origin has been linked to white-light faculae, strong unipolar magnetic fields, or small magnetic loops, and their variability
over the solar cycle makes them an essential diagnostic of long-term polar activity. Investigating these phenomena is key to advancing our
understanding of the long-term evolution of the polar atmosphere and the processes by which energy is transported and dissipated in the corona.

The solar chromosphere exhibits a variety of waves originating from the photosphere and deeper layers, causing oscillations at different
heights with distinct frequencies. This study identifies and analyse atmospheric gravity waves (AGWs) and acoustic waves at various height pairs
within the solar atmosphere utilizing H-alpha, Ca II IR, and Fe I 6173 \AA imaging spectroscopic observations from Swedish 1-m Solar Telescope. We
study and compare oscillations by analysing power maps generated using velocities obtained from the filtergram difference and bisector methods.
Our analysis shows a consistent increase in power with height in the solar chromosphere for both methods. In addition to this, our results show that
AGWs are detected within or near-magnetic flux concentration regions, where spicules are also predominant, exhibiting significant power in the
chromosphere. These regions also feature inclined magnetic fields, which might be contributing to the propagation of these low-frequency AGWs in the
chromosphere. Examining average power maps at spicule locations reveals
significant power at AGWs frequency across different chromospheric heights. We speculate that these AGWs propagate upward along spicular structures and
were not previously detected in the studies employing space-time map due to their limited lifetime. This study provides insights into the complex
dynamics of solar chromospheric waves influenced by magnetic field, contributing to our understanding of AGWs and acoustic waves propagation across different layers of the solar atmosphere.

 Navigation with Indian Constellation

Solar flares are sudden, explosive events on the Sun in which the magnetic energy gets converted into heat and acceleration of
charged particles along with a rearrangement of magnetic field lines by the process of magnetic reconnection. Energy released in a solar
flare can vary over a large range between 10^23 - 10^32  erg. The energetically large flares, under suitable conditions, affect the
near-Earth space weather and have been studied extensively. Contrarily, microflares and nanoflares are relatively less explored in
terms of their magnetic configuration and reconnection mechanisms, since their detection requires more sensitive observations. However, a
systematic and holistic study of these flares can contribute to the physics of small-scale energy release events and their role in
research problems related to both chromospheric and coronal heating. Consequently, this study focuses on exploring a GOES B-class flare-loosely classified as a "microflare" through a combination of
multi-instrument data, augmented with a three-dimensional data-constrained magnetohydrodynamics simulation. The expectation is
to use the synergy between observations from XSM (Solar X-ray monitor) on board Chandrayaan-2, GOES, AIA, HMI onboard SDO, and
data-constrained MHD simulations using the well-established EULAG-MHD model to develop a framework aiming to understand the small-scale
energy release events in the solar corona.

Transients in the solar atmosphere are fundamental drivers of space weather, making their origins a central focus of solar physics. Solar
flares, often accompanied by coronal mass ejections and jets, release up to 10^32 ergs of magnetic energy within minutes, accelerating particles to
tens of MeV and producing broadband electromagnetic emissions that can perturb Earth's magnetic environment. Hence solar flares and their
associated small-scale jets play a crucial role in mass and energy transport from the lower solar atmosphere to the corona, thereby
contributing to solar wind acceleration. Despite extensive observational and theoretical efforts over recent decades, key questions in this field
remain unresolved: Where and how are particles accelerated during flares? Do chromospheric signatures provide important information of imminent solar
eruptions? Can fine-scale flare ribbon structures reveal details of the coronal reconnection process? Leveraging high-resolution ground-based and
space-borne observations, this work aims to address these questions and advance our understanding of solar flares.