Udaipur Solar Observatory Seminars

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.

Solar radio observations provide access to the solar corona,
heliosphere, and ionosphere and are considered to be an excellent
indicator of disturbances in the solar atmosphere. They offer
immediate signatures of energetic solar transients, such as solar
flares and coronal mass ejections.

In this talk, I will begin with a basic introduction to solar radio
observation, covering how radio waves are generated, how they
propagate, and how they escape into the interplanetary medium. I will
then discuss the different emission mechanism processes and density
models, help us interpret radio observations. Then I will explain how
radio emissions are linked to the energetic transient event in the
solar atmosphere. Furthermore, I will introduce the various
spectroscopic and imaging instruments used for solar radio
measurements, including both ground-based and space-based instruments.
Using dynamic spectra, we can identify and analyze different types of
radio bursts, which are mainly classified into five types (Types I-V).
Then, finally, I will share my preliminary work related to such
phenomena.

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.

Scientists and researchers opt for telescopes with larger diameters to unravel the mysteries of the universe by having high-resolution observations. However, the ground-based telescopes' resolution suffers from the Earth's atmospheric turbulence. However, atmospheric turbulence causes degradation in the image quality of the ground-based telescopes. To understand the degradation in image quality and to develop methods to mitigate the effects of atmospheric turbulence, it is essential to quantify the strength of atmospheric turbulence for a given observational site. The measurement of the strength of atmospheric turbulence could be done through a parameter known as Fried parameter. In this project, two methods are explored to estimate Fried parameter at Udaipur Solar Observatory (USO) and implemented by obtaining suitable observations in the visible wavelengths. Preliminary results obtained will be discussed.

The outermost layer of the Sun's atmosphere, known as the corona, has temperatures reaching over a million degrees Kelvin. This layer contains low-density plasma and exhibits well-organized structures like helmet streamers, polar plumes, coronal holes, coronal loops, etc. Numerous investigations have been conducted in the past few decades following the availability of coronal observations. Nonetheless, a few issues are still not fully understood. We explore a few of them by utilizing high spatial and temporal resolution observations from various space-based observatories across different wavelength bands. We examine the oscillatory properties in the coronal loops within various active regions, depicting the presence of decaying and decayless loop oscillations in the fundamental mode. We estimate the energy flux and the dissipation of this energy, considering the damping mechanisms such as resonant absorption, wave leakage, etc., to heat the coronal plasma. Similarly, we examined the presence of higher overtones in other coronal loops and estimated the density scale height and loop expansion factors in terms of the oscillation period ratios of loops. After that, we applied coronal seismology and nonlinear force-free field (NLFFF) extrapolation methods to validate the coronal magnetic field strength. In summary, we concluded that different waves and oscillations can be studied with the help of different analysis methods, and hence used to estimate the coronal plasma parameters, to understand the cause of the coronal heating and acceleration of solar wind.

Earth-directed solar coronal mass ejections (CMEs) are the primary drivers of space weather disturbances. A good understanding of CME thermodynamics is therefore crucial to better characterize their geoeffictiveness in advance. The heating of CME plasma remains one of the fascinating and unsolved problems in the domain of heliophysics. CMEs expend their energy in heating charged particles to compensate for the cooling that occurs as they expand. Due to its omnipresent nature in astrophysical plasma, turbulence plays a central role in governing the thermodynamics of CMEs and solar wind as they propagate through the interplanetary space. In this study, we use the in-situ data of a large sample of well-observed near-Earth CMEs observed by the Wind spacecraft. The in-situ observation technique provides us with a unique way to look into the internal physics of CMEs along the line of intercept between the CME and the spacecraft. Such observations thus help us to quantify the turbulent fluctuations in different parameters such as plasma density, speed, and magnetic field. In the first part of this talk, we will use the turbulent fluctuations to estimate the anomalous resistivity which is arising due to the stochastic scattering of charged particles in the turbulent medium. This resistivity can supplement the Joule heating in near-Earth CMEs, making turbulence one of the sources of local heating in CME plasma. The thermodynamic state of CME plasma is often described using a polytrope. In the second part of the talk, we will quantify the power that is stored in those turbulent fluctuations and compare it with a model by varying the polytropic index. If all the power that is stored in the turbulent fluctuations goes into heating the protons of near-Earth CME plasma, the polytropic index will be approximately 1.35. Such findings therefore contribute to better understanding the CME thermodynamics, thereby improving CME propagation models and estimates of Earth arrival times.

Solar jets are collimated, beam-like plasma ejections and are ubiquitous in solar atmosphere. They are crucial for understanding solar activities at different scales, such as magnetic reconnection, coronal heating, and particle acceleration. Recent advances in theoretical modelling, observations, and simulations have improved our understanding of solar jets, particularly their triggering and driving mechanisms, as well as the magnetic topology involved. However, many aspects remain unresolved and continue to be active areas of research. In this seminar, we will review the current understanding of solar jets and, based on data-constrained magnetohydrodynamic simulations and observational analysis, explore the magnetic topology and mechanisms responsible for jet initiation. 

Solar radio bursts can provide important insights into the underlying physical mechanisms that drive small- and large-scale eruptions on the Sun. Since metric radio observations give us direct access to the inner and middle corona, they are valuable tools for monitoring and understanding coronal dynamics. Type II metric radio bursts are signatures of coronal shocks and serve as proxies for observations in the height range of ~1.1-2.5 R_sun. We studied a multilane type II radio burst with clear signatures of both fundamental and harmonic lanes, each exhibiting split bands. Interestingly, the harmonic band showed further splitting at lower frequencies. Preliminary analysis using radio imaging suggests multiple electron acceleration sites, as seen by Nancay Radioheliograph (NRH) data. Our findings point to the flanks of a CME/EUV disturbance as the origin of the burst lanes, indicating that strong lateral expansion likely led to the observed emissions. 

Determination  of solar coronal plasma diagnostics such as temperature, density, and  abundances require spectroscopy at high energies (EUV and X-rays).  Traditional slit-based instruments achieve high spectral resolution  through long, narrow slits. 2D pure spectral images are created by  stepping the slit, called raster, over the region of interest. During  the raster process, we lose co-temporal observations of the spatial  structures at high temperatures (> 5MK). This difficulty can be  overcome with slitless spectrograph instruments, which can take a  snapshot of a wide field of view on the Sun, with dispersed spectral  images overlapped from different spatial locations on the Sun. Such data  are called spectroheliogram (or) overlappogram. Due to the difficulty  of unfolding the overlapping spatial and spectral information, such  instrument was last flown successfully in Skylab and were abandoned since 1970s.  The  Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) is a slitless spectrograph that operates in the soft X-ray wavelength range (8 - 30  Angstroms) to capture this critical data set.  Till date MaGIXS had two successful flights, 30 July 2021 and 16 July  2024 respectively. MaGIXS demonstrated the successful unfolding of spatial-spectral overlapped datasets to determine spectrally pure images from a wide-field of view. During  its first flight, MaGIXS-1 observed several diagnostic emission lines  to constrain frequency of heating in coronal structures. In this talk I  will present the science highlights from MaGIXS-1, describe exciting  MaGIXS-2 observations from the recent 2024 flight and discuss plans for  the upcoming MaGIXS-3 solar flare campaign.

The plasma-beta is an important fundamental physical quantity in solar plasma physics, which determines the dominating process in the solar atmosphere, i.e., magnetic or thermodynamic processes. Here, for the first time, we provide variations of magnetic field and plasma-beta along magnetically structured loops from the photosphere to the corona. We have selected several fan loops rooted in sunspot umbra observed simultaneously by the Interface Region Imaging Spectrograph and Solar Dynamics Observatory. The 3-min slow waves enabled us to trace and analyze several fan loops with cross-sectional areas in the lower atmosphere and locate their footpoints at the photosphere. We find the RMS magnetic field strengths in the range 1596-2269 G at the photospheric footpoints of the fan loops, which decrease rapidly to 158-236 G at the coronal footpoints. We estimated the plasma-beta at the photospheric and coronal footpoints in the range 0.2-0.5 and 0.0001-0.001, respectively. We found plasma-beta<1 along the whole loop, whereas the plasma-beta~1 layer is found to be at sub-photospheric heights. We compared our findings for isolated individual fan loops with a previously established model for active regions and found an almost similar pattern in variations with height, but with different plasma-beta values. Our results demonstrate the seismological potential of 3-min slow waves omnipresent in the umbral sunspot atmosphere to probe and map isolated loops and determine magnetic field and plasma-beta along these loops. The obtained parameters provide crucial ingredients for the theoretical modeling of the umbral atmosphere and wave dynamics along loops.

In many astrophysical systems, mixing between cool and hot temperature gas/plasma through Kelvin-Helmholtz instability-driven turbulence leads to the formation of an intermediate temperature phase with increased radiative losses that drive efficient cooling. The solar atmosphere is a potential site for this process to occur, with interaction between either prominence or spicule material and coronal material, allowing the development of intermediate temperature material with enhanced radiative losses. In this talk, I will present a set of equations to model the evolution of such a mixing layer based on the self-similar evolution of a turbulent layer and use this to make predictions for the mixing-driven cooling rate and the rate at which mixing can lead to the condensation of coronal material. These theoretical predictions are benchmarked against 2.5D and 3D MHD simulations (the latter showing the additional development of the thermal instability). Applying the theoretical model to prominence threads or fading spicules, we found that the mixing would lead to the creation of transition region material with a cooling time of ~100s, explaining the warm emission observed as prominence threads or spicules fade in cool spectral lines without the requirement for any heating. In fact, our results imply that the observations of the solar atmosphere that appear to show cool prominence or spicule material becoming warm are likely to be a sign of cooling of the corona and not heating. I will also take the opportunity to present the SAMS project, a new modelling suite we are developing to understand the complex interplay between dynamics, radiation and ionisation in the solar atmosphere.

Coronal mass ejections (CMEs) are large eruptions of kinetic and magnetic energy from the Sun that travel through the heliosphere. Their propagation is significantly influenced by the ambient solar wind and large-scale magnetic field structures. These interactions can alter the direction and orientation of CMEs, which is crucial for understanding and forecasting space weather. In this seminar, I will discuss ambient solar wind modelling and optimisation and the impact of the solar wind on heliospheric propagation of CMEs. State-of-the-art MHD space weather forecasting frameworks are based upon the Potential Field Source Surface (PFSS) and Schatten Current Sheet (SCS) extrapolation models for the magnetic field using synoptic magnetograms. These models create a solar wind background for the simulations using empirical relation of Wang, Sheeley, and Arge (WSA), at the inner boundary of the heliosphere. We implemented the solar wind velocity prediction framework (PFSS+WSA+HUX and PFSS+SCS+WSA+HUX) during
2006–2011, covering the descending and deep minimum phase of the solar cycle (SC) 23 and the ascending phase of SC 24. Our framework performed well for the descending phase of SC23 and ascending phase of SC24. However an unexpected decrease in the performance of the framework during the deep minimum phase of SC23 was noted which is attributed to the decrease in the observed coronal hole area at low and mid latitudes during this phase. Another important parameter used in the WSA model for solar wind modeling  is the height of the source surface (Rss).  We explore the effects of optimizing the Rss within the WSA model, using three different types of magnetograms from the GONG network. Our findings suggest a need for optimization of Rss, with the SC phase, particularly a lower Rss near the SC maximum and a higher Rss at SC minimum as compared to the standard Rss (2.5R⊙). We also found that forecasting accuracy improved by using zero-point corrected maps as compared to the standard Carrington maps from GONG. In order to understand the role of the solar wind in heliospheric propagation of the CMEs, we tracked 15 Earth-impacting CMEs in the corona and heliosphere. While half of the events expanded self-similarly up to 40 R⊙, the remaining events showed deflection either in latitude, longitude, or tilt.  The analysis reveals that CME rotation is a rare phenomenon observable in the heliosphere and requires conducive conditions of both magnetic field and solar wind environment. We developed a heliospheric solar wind model to serve as the ambient medium for CME propagation, enabling the study of CME interactions with the solar wind. We also implemented the geometrical and magnetic field models of CME flux rope for tracking in the heliosphere and interplanetary magnetic field (IMF) modeling. We successfully demonstrate the above developed models for a few CME/ICME events.  The above developed models can be utilized to comprehensively understand the heliospheric propagation of CMEs and hence the space weather.

lane wavefronts from celestial objects get distorted due to Earth's atmospheric turbulence. This distortion leads to the degradation of the images forming in our optical systems. As a result, it becomes difficult for the astronomers to identify the high frequency features, that are "allowed" by their diffraction limited optical systems, making them seeing-limited. Corrections can always be applied to some extent if the amount of distortion is known. This distortion typically depends upon the strength of the atmospheric turbulence through which the waves have passed before reaching to our optical system. Quantification of the strength of atmospheric turbulence has been done by calculating a statistical quantity known as Fried's parameter associated to the atmospheric turbulence at the site of observation. In this work, Fried's parameter has been estimated for the observation site of Udaipur Solar observatory by using method of angle of arrival fluctuations.

The Sun’s magnetic fields can twist, shear, and wrap around each other. Magnetic helicity helps us measure this behaviour and plays an essential role in understanding how magnetic fields evolve and what triggers coronal mass ejections (CMES). In this seminar, I will present a method to observe magnetic helicity and the associated energy flux. I will highlight how magnetic helicity flux changes during eruptive and confined solar events.

Solar flares are the most powerful explosions in our solar system, releasing up to 1032&#8722;1033 ergs within approximately 10–1000 seconds. During a flare, energy stored in non-potential magnetic fields is suddenly released, a process triggered by magnetic reconnection. Consequently, plasma in the corona and chromosphere is heated to tens of millions of Kelvin, resulting in the striking enhancement of soft X-ray and longer-wavelength emissions. At the primary energy release site, charged particles—electrons, protons, and heavier ions—are accelerated to high energies, emitting hard X-rays and &#947;-rays. We carry out a multiwavelength analysis of two consecutive flares of GOES classes C6.3 and M1.0, categorized as confined and eruptive, respectively. At the time of the flares, the Solar Orbiter was at 0.3263 AU from the Sun, with a light travel time to Earth of 335.2 seconds. The angular separation between Earth and Solar Orbiter was 85.1 degrees. XSM observes the spectrum in the 1–15 keV band, covering the thermal part of the solar flare spectrum, while STIX provides the spectrum in the complementary 4-150 keV energy range, covering the non-thermal part. Additionally, STIX provides X-ray images of the flare sources using an indirect imaging technique. Time-resolved spectra from both instruments were analyzed independently and then jointly modeled to infer the thermal and non-thermal parameters of the flares more precisely. We find that the XSM spectra are well fitted with a two-temperature model, the STIX spectra are well fitted with an isothermal and thick-target bremsstrahlung model, and the joint fitting of XSM and STIX spectra fits well with a two-temperature thermal model combined with a thick-target bremsstrahlung model. Combined fitting of XSM and STIX spectra provides better constraints on the estimation of thermal plasma parameters. We also use complementary imaging observations at longer wavelengths from AIA/SDO to understand the dynamics of coronal magnetic loops before and during the eruptive phenomena.

The solar atmosphere is dominated by intense magnetic activities where strong heating events occur throughout the different layers of the atmosphere. Small-scale transient events, such as UV Bursts, nanoflares, spicules, and small-scale jets are thought to play a crucial role in transferring energy from the Sun’s lower atmosphere to its outer layers. When observed in Ca II filters, the solar chromosphere constantly shows several small-scale compact brightening events. These brightenings are omnipresent in active region plage and could potentially contribute to the heating of active region plasma. In this study, we analyze narrow-band images of the Ca II 8542 Å line acquired on 7 December 2022 with the Multi Application Solar Telescope (MAST). These observations are complemented by multi-channel data from the Atmospheric Imaging Assembly (AIA) to investigate the thermal evolution of the events, and by Helioseismic and Magnetic Imager (HMI) magnetograms to explore magnetic field evolution and signatures of possible reconnection.

Quiescent prominences are large magnetic structures hosting cool (~10,000 K) plasma in the surrounding million-degree solar corona. Prominences host different flows that may distort magnetic field lines, which may lead to magnetic reconnection inside the prominence body. In this seminar, I will discuss the investigation of bi-directional flows in a quiescent prominence, observed using the narrow band imager of the Multi-Application Solar Telescope (MAST), Udaipur. The Ca II 8542 Å line scan observations from the MAST telescope were complemented with Extreme Ultra-Violet (EUV) intensity images from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). We observed bi-directional flow patches inside the prominence, hosting flow of the order of 10 km/s in the line of sight and plane of the sky of prominence. The bi-directional plasma flows were multi-thermal in nature. The plasma dynamics associated with the bi-directional flow patches point toward their possible association with magnetic reconnection inside the prominence.

The interior of the Sun is opaque to electromagnetic radiation. However, the Sun's dynamic atmosphere hosts a rich spectrum of waves and oscillations, providing a unique diagnostic tool for investigating both its internal structure and outer layers. This talk will explore the application of seismological techniques to infer the physical properties of the solar interior and the magnetized plasma in the corona. We will discuss current research advancements and the limitations of these methods in unraveling the Sun’s complex structure. By investigating how acoustic and MHD waves propagate through the Sun’s interior and atmosphere, we can gain insights into the interactions between plasma dynamics, magnetic fields, and the mechanisms driving energetic activities such as solar flares, coronal mass ejections, and more.