Direct measurements of solar irradiance started in 1978, which is a rather short period for climate studies. Irradiance variations on timescales of days and longer are attributed to the evolution of the solar surface magnetic field, which allows irradiance reconstructions for periods that appropriate data describing solar surface magnetism exist. In particular, such models require information...
The solar cycle is driven by the emergence and evolution of active regions on the Sun’s surface, which play a critical role in the Sun's magnetic dynamics. One of the fundamental properties of these regions is the tilt angle, which describes the inclination of a sunspot group’s axis relative to the solar equator. Tilt angles are essential for understanding the solar dynamo, as they contribute...
The large-scale convection in the sun, supergranulation, is manifested as a network structure on the solar surface. The network cells have an average lifetime of 24 hours, a size of about 30 Mm, and a lane width of about 6 Mm. We have obtained the lane widths and intensities of the network as functions of latitude and time from the Ca II K spectroheliograms of the 100-year Kodaikanal archival...
Time series of regular full-disc solar observations acquired in white light and at the Ca II K and Halpha lines provide direct information on magnetic regions on the Sun with an almost complete daily coverage over the last century. This makes them extremely important for studies of the solar magnetism over long time scales. Here, we first provide an overview of the most prominent archives of...
In this talk, I will present an analytical model that unifies many of the solar inertial waves as a single family of mixed inertial modes. Here, mixed modes refer to the prograde- and retrograde-propagating members of this family. Thermal Rossby waves exist as prograde-propagating waves, while the high-frequency retrograde (HFR) wave is possibly a member of the retrograde branch. The higher...
The past several years have seen a dizzying array of both modeled and observed inertial oscillations in the solar convection zone. While classical Rossby waves are relatively well understood, the recently observed high-frequency retrograde vorticity (HFR) modes lack a convincing theoretical explanation. There have also been several different types of retrograde inertial waves that have been...
The Sun's meridional circulation is crucial to understanding its dynamo and interior dynamics. However, helioseismic determination of deep solar meridional flows is complicated by multiple systematic effects, leading to inconsistent results in previous studies. To find the cause of the discrepancies, we collect measurement codes from multiple previous studies and analyze over 13 years of HMI...
The basic concepts underlying our current understanding of solar and stellar magnetic activity cycles as being due to an internal dynamo process were laid out in more or less their current form some 70 years ago. Yet, at this writing, there exist no concensus "dynamo model of the solar cycle"; be it at the level of the relative importance of various potential inductive processes, of the...
The solar magnetic cycle is crucial for understanding solar activity and space weather. Two key models for studying it are the Surface Flux Transport (SFT) model and the 3D Babcock-Leighton dynamo model, respectively. The SFT model examines large-scale magnetic field evolution on the Sun's surface to predict solar cycles. In contrast, the 3D Babcock-Leighton model explores internal processes...
The 11-year sunspot cycles undergo amplitude modulation over longer timescales. As a part of this long-term modulation in solar activity, the decennial rhythm occasionally breaks, and sunspots disappear from the solar surface for multiple decades, leading to a period of magnetic quiescence on the Sun – known as the solar grand minimum. Observation of solar magnetic activity proxies suggest...
I describe some of the defining observations of the solar cycle that provide insights into the dynamo process, including the basics such as Hale and Joy's law, the spatio-temporal emergence of active regions that creates the butterfly diagram, and large-scale flows including zonal, meridional, etc. I also discuss new research on activity nests and active region flux emergence patterns....
In the solar atmosphere, active regions are dominated by the magnetic field, its complex topology and evolution. To understand the divers nature of active regions, we study a large sample of 3D magnetic field configurations to derive general properties relating magnetic flux, magnetic energy and magnetic field scale-height. We compute the magnetic fields under the potential field assumption...
Using the helioseismic data for the last nearly 30 years from GONG, MDI and HMI instruments it is possible to study the solar cycle variations in structure and dynamics. Variations in frequencies are found to be correlated to solar activity and the inversion of these frequency differences, shows that the variation is confined to near surface region and is generally attributed to variation in...
Using solar-cycle long measurements of meridional and zonal flows in the near-surface shear layer (NSSL) of the Sun, we study temporal variations in them and their connections to active regions. We find that inflows towards active regions are part of a local circulation with an outflow away from active regions at depths around 0.97 R$_\odot$, which is also the location where the deviations in...
The tachocline, a thin shear-layer located in a subadiabatic region at/near the base of the solar convection zone, can be modelled using a 3D thin-shell shallow-water type formalism. In such models the Sun's global differential rotation and toroidal magnetic fields undergo nonlinear dynamical interactions by exchange of energies among differential rotation and toroidal magnetic fields, and...
The solar convection zone is characterized by the birth of the concentrated magnetic field regions known as Bipolar Magnetic Regions (BMRs), which are tilted with respect to the equatorial line. The thin flux tube model, employing the rising of magnetically buoyant flux loops twisted by the Coriolis force, is a popular paradigm to explain the formation of the tilted BMRs. In this study, we...
We cannot directly observe the magnetic field vector on the surface of the Sun, only infer it from observations using a model. Therefore, our ability to obtain an accurate picture of the magnetic topology, strength and connectivity in the outer layers of the Sun, relies on having high signal-to-noise observations and a robust model that can be used to fit the observations. Such requirements...
This talk reviews recent accomplishments and current status of dynamic high-resolution high-cadence measurements of coronal magnetic field and plasma parameters in solar flares. Such measurements are of exceptional importance, particularly because release of the magnetic energy due to reconnection is believed to drive such transient solar phenomena as solar flares, eruptions, and jets. This...
The Hα line is widely utilized for studying the solar chromosphere, but there is a scarcity of polarimetric studies aimed at inferring magnetic fields. One of the many reasons could be that there are no polarimetric studies of the Hα line utilizing 3-D radiative transfer, and earlier 1-D radiative transfer studies suggested a significant contribution of the photospheric fields in the Stokes V...
Space weather is largely caused by the activity of our Sun. Invisible yet powerful magnetic fields, created within the Sun, determine when and where the next solar eruption will happen. In this talk, I will review how advances in solar observations and data-driven models allowed scientists to understand flare magnetism in a lot more detail than ever before. I will overview highlights of...
Recent high-resolution solar observations have unveiled the presence of small-scale loop-like structures in the lower solar atmosphere, often referred to as unresolved fine structures, low-lying loops, and miniature hot loops. These structures undergo rapid changes within minutes, and their formation mechanism has remained elusive. In this study, we conducted a comprehensive analysis of two...
Regular measurements of the magnetic field in the solar corona are critically lacking, hindering investigations of key physical processes involved in coronal heating, solar wind generation, and explosive eruptions such as flares. Using a CME model of the Predictive Science Inc., we synthesized observations from the upcoming COronal Solar Magnetism Observatory (COSMO) Large Coronagraph (LC),...
I will review recent progress in observations and numerical simulations of the dynamics of the solar chromosphere. During the last decade, novel high-resolution space-based and ground-based instrumentation has provided new views of the role of shocks, jets, waves, and magnetic reconnection in the dynamics and energetics of the chromosphere and the layers above. These observations have been...
Recent high-resolution observations have shown that quiet-Sun Ellerman bombs (QSEBs), thought to be driven by magnetic reconnection in the deep solar atmosphere, are more prevalent than previously known, with about 750,000 present across the quiet Sun at any given time. Analyzing H$\beta$ and H$\epsilon$ observations from the Swedish 1-m Solar Telescope, we detected ubiquitous QSEBs...
We perform radiation magneto-hydrodynamic simulations of the solar atmosphere, driven self consistently by sub-surface convection, thereby producing a forest of spicules commensurate with the observed properties (Dey et al, 2022, Nat Phys). By varying the strength of the imposed magnetic field (mimicking the dynamo generated large scale field of the Sun), we show that kinematic properties of...
We investigate vortex dynamics in three magnetic regions, viz., Quiet Sun, Weak Plage, and Strong Plage, using realistic three- dimensional simulations from a comprehensive radiation-MHD code, MURaM. We find that the spatial extents and spatial distribution of vortices vary for different setups even though the photospheric turbulence responsible for generating vortices has similar profiles for...
The question of what heats the outer solar atmosphere remains one of the longstanding mysteries in astrophysics. Statistical studies of Sun-like stars reveal a correlation between global chromospheric and coronal emissions, constraining theoretical models of potential heating mechanisms. However, spatially resolved observations of the Sun have surprisingly failed to show a similar correlation...
The solar atmosphere is populated by ubiquitous swirling structures, believed to play a crucial role in exciting various magnetohydrodynamic waves, pulses, as well as spicules. However, their small scale and short lifespan have posed significant challenges to automated detection, hindering comprehensive studies of their statistical and collective behavior. This talk summarizes recent...
A new era of high-resolution solar observations, driven by advancements in ground-based, balloon-borne, and space-based facilities (e.g., SST, DKIST, ALMA, SUNRISE, and Solar Orbiter, among others), has revolutionised our understanding of magnetohydrodynamic (MHD) waves in the solar atmosphere in recent years. These cutting-edge facilities provide unprecedented high-resolution observations,...
The Sun's dynamic atmosphere is rich in magnetohydrodynamic (MHD) waves, particularly in regions of intense magnetic activity like sunspots, where these waves are most pronounced and powerful. These waves in sunspots may play a crucial role in providing energy for plasma heating and contribute to the early stages of solar wind formation, and they can also serve as valuable diagnostic tools for...
The chromosphere exhibits various acoustic waves that are generated in the photosphere or deeper layers due to convective motions. As these waves encounter the steep density gradient between the photosphere and the chromosphere, they transform into shock waves, often characterized by a sawtooth pattern in λ-time plots of chromospheric spectral lines, such as Hα and Ca II. In this study, we...
The solar atmosphere is now understood as a fully interconnected system, where dynamic events in one layer may be the cause or effect of those occurring in the layers above. Photospheric flows, through interactions with magnetic structures, facilitate energy transfer to the chromosphere and beyond, often in the form of waves. These processes depend on frequency, with evidence suggesting that...
Observations often suggest that the solar coronal loops are multi-stranded and multi-thermal at the current instrument resolution. The goal of this work is to study the effect of this multi-strandedness on the propagation and damping of compressive slow magnetoacoustic waves. We employ an ideal 3D MHD numerical model to achieve this objective. The simulation results are forward modelled to...
The Extreme UV Imager (EUI) on-board Solar Orbiter consists of three telescopes, two high-resolution imagers providing information on the corona and the chromosphere, and an EUV full-disk imager that does not only allow to observe the whole solar disk but provides us with unprecedented information of the corona far above the limb in a coronagraphic mode. Hence, the scientific results through...
Aditya-L1, is an observatory class mission to study the solar dynamics and its influence in the inner heliosphere especially at the first Sun-Earth Lagrangian (L1) point. Aditya-L1 conceived with four remote sensing and three in-situ payloads. The remote sensing payloads carry out observations of the source regions of the dynamical events while the in-situ payloads observe the events at L1....
The European Solar Telescope (EST) will be equipped with a comprehensive suite of state-of-the-art intruments designed to observe the solar atmosphere at high spatial and temporal resolution and high polarimetric sensitivity. Among them are three Tunable-Imaging Spectropolarimeters/Fixed-Band Imagers (TIS/FBIs) that will provide diffraction-limited measurements of photospheric and...
Jets permeate the upper solar atmosphere, from the powerful and extended coronal jets to the smaller but more abundant spicules. They appear as a natural bridge to transport mass and energy from the surface to the upper atmosphere, and possibly also drive the solar wind. I will review the progress made over the last few years, in particular about the elusive spicules. The age old question of...
Here we present the magnetic origin of different types of campfires and coronal jets, using line-of-sight magnetograms from Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager together with extreme ultraviolet images from Solar Orbiter/ Extreme Ultraviolet Imager and SDO/Atmospheric Imaging Assembly. We find that (i) both campfires and coronal jets reside above neutral lines and...
Small-scale Brightenings (SBs) are commonly observed in the transition region that separates the solar chromosphere from the corona. These brightenings, omnipresent in active region patches known as “moss” regions, could potentially contribute to the heating of active region plasma. In this study, we investigate the properties of SB events in a moss region and their associated chromospheric...
Advancements in instrumentation have revealed a multitude of small-scale extreme-ultraviolet (EUV) events in the solar atmosphere and considerable effort is currently undergoing to unravel them. Our aim is to employ high-resolution and high-sensitivity magnetograms to gain a detailed understanding of the magnetic origin of such phenomena. We used coordinated observations from the Swedish 1-m...
The extreme-ultraviolet (EUV) brightenings identified by Solar Orbiter (SolO), commonly known as campfires, are the smallest detected, to date, transient brightenings or bursts observed in the non-active regions of the lower solar corona. Campfires have been proposed to be the finest-scale members of the nanoflare family. Our understanding about the role of campfires in coronal heating stands...
Dissipation of electric current due to magnetic reconnection provides a viable physical mechanism for the heating and dynamics of solar plasma. However, magnetohydrodynamic (MHD) waves may also contribute to its dynamics and heating. External wave-like perturbations may drive reconnection in the solar chromosphere and corona, but coalescing plasmoids in a reconnecting current sheet can also...
Coronal mass ejections (CMEs) and flares are the most energetic explosive phenomena occurring in the solar atmosphere and subsequently propagating into the interplanetary space, probably affecting the safety of human high-tech activities in the outer space. To understand and predict the transient events, we need to elucidate some fundamental but still puzzled questions, one of which concerns...
Coronal mass ejections (CMEs) can create the most hazardous space weather effects. Therefore it is extremely important to advance our understanding of how they start in the corona, which would be useful for scientifically and accurately predicting them. This may be partially achieved by studying the signatures that CMEs may leave in the low corona as identified in Extreme Ultraviolet (EUV)...
Solar jets are highly collimated plasma flows accelerated along magnetic field lines due to magnetic reconnection, often originating from anemone-shaped arcades. These impulsive jets, particularly broader ones, frequently exhibit untwisting motions. In this study, we analyze a solar jet associated with a circular flare ribbon using high-resolution data from the Swedish 1-meter Solar Telescope...
Jets are one of the eruptions which impact the solar atmosphere significantly along with other transients like solar flares and coronal mass ejections (CMEs). Magnetic reconnection is believed to be one of the reasons behind these transients. The onset and factors contributing to the morphology and thermal structures are still complex to comprehend. In order to understand them, we have studied...
Field stored just below or rising to the photosphere will break through the surface and enter the upper atmosphere once the gradient of the sub-photospheric field strength becomes sufficiently large. Driven by convective motions and the expansion of field in the chromosphere’s low-β plasma, opposite polarity flux bundles will reconnect. Some of this emerging flux is likely due to a local...
Solar Energetic Particles (SEPs) from suprathermal (few keV) up to relativistic (~few GeV) energies are accelerated at the Sun in association with solar flares and coronal mass ejection (CME)-driven shocks. In this review, we present important recent results of the study of Interplanetary CMEs and shocks in relation to energetic particle acceleration and transport, taking advantage of...
One of the main objective of the Solar Orbiter mission is concerned with the production of energetic particles in the heliosphere, in particular with understanding how particles are released from their acceleration sources and distributed in space and time in the heliosphere. For energetic electrons, part of this question can be addressed by combining X-ray and radio observations. Indeed,...
We report observations of <500 keV/nucleon suprathermal (ST) H, He, O, and Fe ions in association with several crossings of the heliospheric current sheet that occurred near perhelia during PSP encounters 7-18. In particular, we compare and contrast the ST ion time-intensity profiles, velocity dispersion, pitch-angle distributions, spectral forms, and maximum energies during the three HCS...
We analyze two solar flares—an X-class flare from October 28th, 2021, and an M-class flare from November 29th, 2020—to investigate the dynamic changes in thermal energy during their evolution. Our study uses data from several sources, including the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO), the X-ray Telescope (XRT) on Hinode, and the Spectrometer/Telescope for...
National Large Solar Telescope, a state-of-the-art 2-meter telescope, is designed to revolutionize solar atmospheric research. Its primary goal is to conduct high-resolution observations, both spatially and spectrally, of the Sun's outer layers. To ensure optimal performance, a rigorous site characterization program was initiated in 2007. This led to the selection of two prime locations in the...
Since its installation in 2012, the Gregor Infrared Spectrograph (GRIS) has been operating with a single detector that could be tuned to any wavelength in the bands 1.0-1.3 microns or 1.5-1.8 microns in spectroscopic or spectropolarimetric mode, or in the band 2.0-2.3 microns in spectroscopic mode. Few years ago, a removable integral field unit (IFU) was added to the system to make the...
Solar coronal EUV/X-ray bright points (CBPs) are believed to be major contributors to quiet solar coronal heating. Solar Orbiter's EUI/\hri\ observations of an emerging flux region (a typical CBP) in 174 \AA, emitted by the coronal plasma at $\sim$1 MK, reveals the presence of numerous tiny bright dots. These dots are roundish with a diameter of 675$\pm$300 km, a lifetime of 50$\pm$35 seconds,...
The Gauribidanur Radio Observatory (GRO) is one of a few solar radio observatories functioning for the past few decades. It has four major facilities, viz., the Gauribidanur RAdioheliograPH (GRAPH), the Gauribidanur LOw-frequency Solar Spectrograph (GLOSS), the Gauribidanur Radio Interferometric Polarimeter (GRIP), and the Gauribidanur RAdio Spectro-polarimeter (GRASP). The GRAPH...
Suprathermal particles (with energies in the range from 10s of keV to 1-2 MeV) are thought to be the seed populations for solar energetic particles accelerated by shocks associated with interplanetary coronal mass ejections (ICMEs). Origins, energizations, and modulations of suprathermal particles in the interplanetary (IP) medium have been widely debated in the contemporary space era, thanks...
Simultaneous monitoring of stellar brightness and chromospheric activity shows that the brightness variations of stars with near-solar level of chromospheric activity appear to be faculae dominated over their activity cycle, whereas they are spot dominated at higher chromospheric activity. Additionally, the unprecedented precision of broadband stellar photometry achieved with the...
Meridional flow is crucial in generating the solar poloidal magnetic field by facilitating the poleward transport of the field from the decayed Bipolar Magnetic Regions (BMRs). As the meridional circulation changes with the stellar rotation rate, the properties of stellar magnetic cycles are expected to be influenced by this flow. In this study, we explore the role of meridional flow in...
The distribution and evolution of photospheric magnetic fields in sunspots, plages, and network, and variations in their relative flux content, play key roles in radial velocity (RV) fluctuations observed in Sun-as-a-star spectra. Differentiating and disentangling such magnetic contributions to RVs help in building models to account for stellar activity signals in high-precision RV exoplanet...
Explosive mass ejections triggered by magnetic activities are common on our Sun and other stars in the Universe. However, there is a lack of evidence for such explosive phenomena in magnetized or partially magnetized planets with atmospheres. Here we present direct evidence for explosive mass ejections from the Martian ionosphere, resulting from magnetic reconnections between strong crustal...
The Sun is variable on timescales ranging from minutes to millenia. Its variability has been shown to be dominantly caused dominantly by the solar magnetic field, with contributions by granular convection and oscillations. Until a decade ago, the known variable stars were distinctly different from the Sun. Their variability was caused by large-scale pulsations, binarity, or, for the most...
Helio- and astero-seismology allow us to extract information on the structure and dynamics of the Sun and stars from the surface to the deeper layers.
Magnetic activity affects the properties of the acoustic modes: at maximum magnetic activity the frequencies of the modes increase while the amplitudes of the modes decrease. This was first observed for the Sun and was applied to many more...
Asteroseismology is the study of oscillations in stars, which helps in understanding their interior structure and dynamics. In the last two decades, NASA's Kepler and TESS space missions have revolutionized the field of asteroseismology by providing vast datasets of photometric time series for hundreds of thousands of stars. In this talk, I will be discussing the application of...
Stellar pulsations offer valuable insights into the internal structure and rotation profiles of stars. The availability of high-quality observations from numerous space-based instruments makes it possible to pursue ensemble analyses on an unprecedented scale. To this end, we have used machine learning to accelerate these studies by several orders in magnitude. I will describe how deep learning...
Understanding the solar activity cycle within the broader framework of stellar magnetic field dynamics is pivotal for comprehending the solar and stellar dynamos. A significant challenge in this pursuit lies in the presence of multiple branches in the relationship between stellar rotation and activity cycle period among main sequence stars. In this presentation, I will elucidate recent...
Like the solar cycle, stellar activity cycles are also irregular. Observations reveal that rapidly rotating (young) Sun-like stars exhibit a high level of activity with no Maunder-like grand minima and rarely display smooth regular activity cycles. On the other hand, slowly rotating old stars like the Sun have low activity levels and smooth cycles with occasional grand minima. We, for the...
Stellar variability presents a significant lower limit to detecting and characterizing exoplanets accurately. Contemporary methods of studying the impact of stellar magnetic fields (in the form of starspots and stellar faculae) involve using simple 1D model atmospheres with a specified effective temperature. We present realistic 3D MHD models of starspots with significant penumbral extent. We...
Magnetized plasma winds and storms from host stars such as the Sun shape (exo)planetary magnetospheres and influence atmospheric mass loss. In the solar system, solar magnetic transients also force planetary environments creating adverse space weather. Magnetohydrodynamic modelling of star-planet interactions provide a physics-based window to explore these phenomena that have profound...
Extreme-precision radial velocity (RV) instruments (e.g., ESPRESSO), offering 10 cm s$^{–1}$ stability, and space telescopes (e.g., JWST), attaining relative flux uncertainties of 10 ppm, are becoming a reality. Such precision is, in principle, sufficient to enable the discovery and characterisation of small rocky planets, including true Earth analogues. However, the intrinsic variability of...
Coronal Mass Ejections (CMEs) are massive eruptions of supersonic magnetized plasma from stellar atmospheres. They create adverse space weather conditions around (exo)planets and can significantly perturb their environment. We investigate how varying ICME characteristics — such as speed, orientation, and magnetic field strength — affect the global dynamics, atmospheric mass loss rates and...
An overview of works on potential distinct behaviors between flaring / eruptive and flare-quiet / non-eruptive solar active regions will be attempted. Focus will be assigned to the most distinctive physical quantities that characterize active regions, namely magnetic energy and helicity budgets, as well as associated non-neutralized electric currents. Emphasis will also be on the single most...
The formation of active nests/longitudes on the Sun may relate to instabilities at the base of the convective zone or the way in which magnetic flux emerges through the solar surface. Persistent hot spots of activity are frequently observed on other Sun-like stars, hinting that their formation may be universal for stars with dynamo-driven magnetic fields. Nested active region emergences...
Coronal mass ejections (CMEs) are the most energetic events originating from the Sun, causing significant and sudden disruption to the magnetic and particulate environment of the heliosphere. Thus, in the current era of space-based technologies, an early warning that a CME has left the Sun is crucial. Our magnetofrictional simulations that capture the global corona's continuous and dynamic...
The integration of medium-term and short-term solar flare predictions is a crucial component of space weather forecasting, given their potential impacts on Earth's technological infrastructure and astronaut safety. This presentation examines the importance of combining medium-term and short-term solar flare prediction methods to improve the reliability and precision of forecasts. Medium-term...
The Interplanetary Magnetic Field (IMF) plays a crucial role in shaping space weather and its impact on Earth's magnetosphere. However, the availability of direct IMF measurements is limited to recent decades, leaving a gap in our understanding of the Sun’s magnetic behavior over longer timescales. To address this, we present a detailed reconstruction of the IMF over the past century by...
Solar Flares release large amounts of energy in the form of radiations in multiple wavelengths. Predicting solar flares starting time and their class is a difficult task. When and at what solar atmospheric layer the flare trigger happens, whether in the corona, transition region or in the chromosphere, is still a puzzle. One way forward is to study the pre-flare signatures in multi-wavelengths...
An extreme event can be defined as an event that falls on the tail of a distribution and characterized by its uniqueness either in its occurrence itself or in its consequences. In the case of the Sun, one talks about coronal mass ejections (CMEs) and flares of extreme energy. Taking one level deeper, one can think of the extremeness of the solar source of these events: active regions and their...
Earth directed coronal mass ejections (CMEs), particularly those with high speeds and southward-pointing magnetic fields, are the main drivers of geomagnetic storms. While the solar wind constantly deposits particles and energy into Earth's magnetosphere, this process is enhanced during geomagnetic storms. One of the most striking effects of these storms is the appearance of auroras. However,...
Constraining the magnetic field strength of coronal mass ejections (CMEs) from observations is one of the key challenges in predicting their space weather impact on Earth. In this work, we present a new method for constraining the magnetic flux of a spheromak CME model in the frame of the EUropean Heliospheric FORecasting Information Asset (EUHFORIA). In this approach, we use the estimated...
This study aims to understand the behavior and characteristics of interplanetary MHD shocks observed at 1 AU using in situ measurements spanning 1996 to 2023. We developed an automated algorithm for shock detection and analyzed the distribution and properties of various shock types, including fast forward, fast reverse, slow forward, and slow reverse shocks. Key shock parameters such as shock...
The alpha (doubly ionized Helium or He2+) to proton (Singly Ionized Hydrogen or H+) ratios (AHe = Na/Np*100) in the solar wind showed distinctive changes in the solar cycle 24 compared to the previous three solar cycles. Further, this ratio is often found to get enhanced in the interplanetary coronal mass ejections (ICME) and gets changed across the stream interface structures of the stream...
In this paper, we present a multi-spacecraft view of the activation of a large magnetic flux rope (MFR) which accompanies a composite flare that evolved into a halo CME. The composite flare consists of an impulsive event during which GOES flux peaked up to C6.3 level and a subsequent long-duration M1.0 event. The term ‘composite’ refers the collective roles of two distinct events of...
The recent in situ observations in the young solar wind made by Parker Solar Probe PSP, revealed a small-scale structuring of the magnetic field that consists of sudden magnetic deflections. These "switchbacks" are particularly pronounced in the radial component of the field, and have a duration of a few seconds to a few hours. These structures are not new but PSP observations uncovered that...
Coronal loops, the arching structures filled with magnetically confined million Kelvin hot plasma, are the prominent features of the solar atmosphere. These loops are best observed in the extreme ultraviolet (EUV) and X-ray wavelengths. Coronal loop emission generally traces the magnetic field lines in the upper solar atmosphere. Thus probing their spatial morphology and evolution will help us...
Solar radio bursts are among the most extensively studied radio phenomena originating in the solar corona and serving as valuable probes of the coronal medium. Their polarization properties are particularly sensitive indicators of coronal magnetic fields, which have historically been difficult to measure. Despite these advantages, instrumental and algorithmic limitations have restricted the...
In principle, the usefulness of radio observations for solar and heliospheric science (heliophysics) is well recognized. In practice, instrumental and algorithmic limitations have kept this promise from being realized. This is now set to change. Several new-generation radio interferometers have recently become available, and more are expected in the near future. These are the many precursors...
Magnetic field measurements in the outer corona and inner heliosphere using remote sensing observations are crucial for improving space-weather prediction. However, routine observations using white-light heliospheric imagers cannot provide these measurements. At radio wavelengths, changes in the polarization angle of background linearly polarized astronomical sources can estimate line-of-sight...
Type-II solar radio bursts are plasma emissions generated by magnetohydrodynamic shocks that are mostly associated with energetic solar eruptions such as CMEs and flares. Several studies have concluded that metric type-IIs are initiated by coronal mass ejections (CMEs). These CMEs are expected to drive shocks and are responsible for giving rise to solar energetic particles (SEPs), the biggest...
Type II solar radio bursts are commonly associated with shocks generated by coronal mass ejections (CMEs), where plasma waves are excited by magnetohydrodynamic (MHD) processes and converted into radio waves at the local plasma frequency or its harmonics. However, there are instances where type II bursts occur in the absence of white-light CMEs. We analyse one such metric type II radio burst...
The long-term evolution of solar filaments, prominently observed in Hɑ, is closely related to the large-scale solar cycle, with their parameters tracing the solar surface magnetic fields and have been long thought to contribute to the polar fields of the next cycle. The Kodaikanal Solar Observatory (KoSO) hosts one of the longest reserves of archival data with the information of these features...
Solar activity is readily observed through the emergence of magnetic structures of varying sizes on the solar surface. While larger magnetic regions have been extensively studied and are well understood, Ephemeral Regions (ERs) represent small-scale, short-lived magnetic features that frequently emerge on the photosphere throughout all phases of the solar cycle. The magnetic flux of ERs ranges...
The space weather inside the heliosphere is dictated by various dynamic processes of the sun; Among these, Coronal Mass Ejections (CMEs) stand out due to their significant impact on space weather. The Geo-effective Interplanetary Coronal Mass Ejections (ICMEs) can trigger severe space weather events, such as geomagnetic storms, which pose substantial risks to modern technological...
Astronomers have uncovered a captivating facet among the myriad celestial bodies, known as Variable Stars. These mysterious entities undergo changes in their radiance over time, offering astronomers a unique opportunity to study the complexities of stars. Since 1911, the American Association of Variable Star Observers (AAVSO) has been diligently monitoring these stars. Variable star...
Solar radio bursts are often byproducts of phenomena like coronal mass ejections (CMEs) and/or solar flares. They are capable of producing very high brightness temperatures and hence lead to a large increase in the observed intensity. Depending upon the details of the physical processes and emission mechanisms involved, their dynamic spectra can show markedly different spectro-temporal...
Magnetic field switchbacks, crucial for understanding solar wind dynamics, are typically identified through magnetic field reversals (Dudok de Wit et al., 2020). This methodology is susceptible to mistakes stemming from data contamination caused by phenomena such as coronal mass ejections (CMEs), flux ropes, magnetic clouds (MICCS), heliospheric current sheets (HCS), partial heliospheric...
The growth of a large-scale magnetic field in the Sun and stars is usually possible when the dynamo number $(D)$ is above a critical value $D_c$. As the star ages, its rotation rate and thus $D$ decrease. Hence, the question is how far the solar dynamo is from the critical dynamo transition. To answer this question, we have performed a set of simulations using Babcock–Leighton type dynamo...
Coronal mass ejections (CMEs), originating from the sun's corona, are large-scale eruptions of plasma and magnetic flux that propagate into interplanetary space, and are capable of significantly influencing the dynamic environment of the inner solar system. Previous studies have established that CMEs exhibit turbulent behavior, characterized by energy cascades from larger to smaller scales...
Sunspot drawings are a unique source of data to retrieve long-term information on the evolution of the solar cycle. The sunspot drawings taken at the Royal Observatory of Belgium (ROB) with the USET observing station cover more than 80 years, and they continue to be made nowadays with the same refractor. Recently, the collection has been fully digitized and analysed.
In this talk, we...
We investigate the handedness in the solar magnetic structures like chromospheric filaments and photospheric active regions using observations obtained from GONG, KSO, and SDO/HMI. At its initial stage near the east limb, we identified a right-bearing sense for the filament barbs and negative helicity in the supporting active region (AR). Subsequently, we observed an emergence of positive...
The Kodaikanal Solar Observatory (KoSO), one of the oldest solar observatories, possesses hand-drawn suncharts that depict various solar features such as plages, filaments, sunspots, and prominences, each marked with distinct colors. These suncharts are valuable for addressing the data gap in the Ca II K dataset of KoSO from 1980 to 2007, which resulted from plate damage and changes in...
Stellar surface inhomogeneities presented by convection, magnetic spots, bright plages, and faculae are recognized as important in the accurate retrieval of exoplanet properties as they can be a source of noise and confusion in stellar radial-velocity (RV) measurements. The identification and characterization of exoplanets around Sun-like stars are impacted by changes in intensity and other...
The solar corona and solar wind are often observed to have elemental abundances different from the solar photosphere, and the observed fractionation appear to depend on the element's first ionization potential, and it is thought to be linked to the processes leading to the solar atmospheric heating. We have used coordinated coronal (Hinode/EIS) and chromospheric and transition region (IRIS)...
We presents a comparison of plasma dynamics in Coronal Holes (CHs) and Quiet Sun (QS) through observations and 2.5D MHD flux emergence simulations. We observe these regions in chromospheric and transition region lines of IRIS as a function of the underlying photospheric magnetic field (|B|). We find excess intensity (blue, redshifts) in QS(CH) with |B|. We observe persistent upflows,...
The solar corona is a dynamic environment that contains various magnetic structures, such as coronal loops, coronal holes, polar plumes, etc. These structures are perturbed by energetic activities such as solar flares, coronal mass ejections, and magnetohydrodynamic waves, leading to oscillations that serve as indirect tools for investigating the properties of the coronal atmosphere. In this...
Helioseismology can detect active regions on the Sun’s far side days before they rotate onto the Earth’s side, using solar acoustic oscillations. These far-side maps provide an important input for space weather models. Recent advances in theoretical and computational helioseismology have improved far-side imaging, which enables high-confidence detection and daily tracking of medium-size active...
Coronal mass ejections (CMEs) are intense solar phenomena where plasma and magnetic fields are ejected from the Sun, playing a significant role in influencing Space Weather. However, traditional coronagraphs struggle to accurately capture the early stages of Earth-directed CMEs due to projection-related distortions. Coronal dimmings, which manifest as localized reductions in...
The Bipolar Magnetic Regions (BMRs) are intense magnetic regions on the Sun's surface, separated by a neutral line. These regions are thought to emerge in the form of magnetic bundles (flux tubes) due to magnetic buoyancy, rising through the convection zone (CZ) in an east-west orientation with a tilt relative to the equator. It has been observed that statistically, BMRs emerging at higher...
Scattering of anisotropic radiation by atoms in the solar atmosphere generates linear polarization in spectral lines such as the Ca I 4227 Å line. Spectro-polarimetric observations of this line, particularly near the solar limb, reveal significant linear polarization. Modeling this line is essential for understanding the sensitivity of scattering polarization to atmospheric parameters and...
Coronal seismology, an essential tool for diagnosing the physical conditions of the solar corona has gained significant attention due to its ability to probe the solar magnetic field and plasma properties through the study of magnetohydrodynamic (MHD) waves in coronal loops. The oscillating signature of these loops, the key features of the solar corona have been extensively observed through...
Solar jets are described as collimated, beam-like structures that eject plasma along straight or slightly oblique magnetic field lines. They can be observed from the lower solar atmosphere up to the corona, spanning a wide range of temperatures. In this study, we present an analysis of recurrent solar jets observed on 6 March 2022 near the active region NOAA 12960, using data from the...
Active regions are one of the primary sources of solar eruptive events like flares and coronal mass ejections, causing adverse space weather conditions. Complex magnetic field distributions of observed active regions are often quantified using diverse tools and techniques, which are later used for measuring the chance of their eruptivity. Similar tools are also utilised to validate magnetic...
Theory suggests that an ion-neutral velocity drift may exist in the solar atmosphere if the collisional momentum exchange between both species is not large enough. This work aims to offer a fresh perspective on this issue by investigating the drift velocity within the Evershed flow. In a previous analysis (Khomenko et al. 2015), the authors derived the Evershed velocities associated to Fe I...
We will present compelling evidence suggesting the X-line of guide-field magnetic reconnection is not necessarily orthogonal to the plane in which magnetic reconnection occurs. The plane of magnetic reconnection is often referred to as the L-N plane, where L is the direction of the reversing and reconnecting magnetic field and N is normal to the current sheet. The X-line is often assumed to be...
Coronal Mass Ejections (CMEs) are expulsions of magnetized plasma bubbles from the Sun episodically, and they are the potential candidates for severe space weather impacts on the Earth. However, the impact duration of CMEs on Earth is governed by their radial sizes and speeds upon arrival. In our work, we estimate a CME's radial size and instantaneous expansion speed at different instances...
During the solar flares, whole solar atmosphere gets heated; however, the energy deposition process in the lower solar atmosphere is still unclear. In this paper, we present spectroscopic and imaging observations of a small-scale transient of life-time $\approx$2-min and subsequent formation of a hot transient loop of life-time $\approx$4-min in a solar active region. The event is classified...
The solar activity is directly related to its variable magnetic field, which is generated in the Sun's convection zone. Solar activity increases and decreases with the solar cycle strength, popularly measured by the sunspot number (SSN). This activity creates space weather and impacts the interplanetary and Earth's atmosphere. The sunspot number (solar cycle) prediction provides a cutting-edge...
Earth's ionosphere owes its existence to the ionization of the neutral constituents by the Solar Extreme Ultraviolet (EUV) and Soft X-ray (SXR). This results in the creation of ionospheric layers like D, E, and F. These layers are distinct only during the daytime ionosphere, and features can be well noticed at the equatorial latitudes. Each layer has its maximum density at a certain altitude,...
The dynamic connection between the solar corona and the heliosphere is critical for understanding and forecasting space weather. Active regions and solar eruptions, including extreme events, significantly influence the heliospheric environment, with profound implications for Earth's magnetosphere. Leveraging data from new space missions like ASPEX-SWIS from Aditya-L1, Parker Solar Probe (PSP),...
The correlation tracking and wave-front sensing cameras in an adaptive optics system correct the wavefront error by locking to a feature in the image acquired by the sensor. The feature is cross-correlated with a reference image to identify the relative shift between consecutive images in the sub-aperture images of a Shack-Hartmann wave-front sensor. The typical frequency of data acquisition...
Three-dimensional (3D) magnetic nulls are abundant in the solar atmosphere, as have been firmly established through contemporary observations [1]. They are established to be important magnetic structures in solar atmosphere, for example, jets [2] and circular ribbon flares [3,4,5]. The flare emissions at the footpoints of the fan field lines constitute a closed circular flare ribbon. Recent...
Gravity waves are generated by turbulent subsurface convection overshooting or penetrating locally into a stably stratified medium. While propagating energy upwards, their characteristic negative phase shift over height is a well-recognized observational signature. Since their first detailed observational detection and estimates of energy content, a number of studies have explored their...
The theoretical model, excluding meridional flow, magnetic buoyancy, and including the entire α effect from the base of the convection zone to the surface, indicates that multicycle correlations occur near the critical dynamo region, while one-cycle correlations are prevalent in the extremely super-critical dynamo region. These findings align with Kumar et al. (2021), who suggest that...
In a stellar atmosphere, the resonance line polarization arises from scattering of limb-darkened radiation field by atoms. This spectral line polarization is severely affected particularly in the wings, when the line photons suffer scattering on electrons in thermal motion. Electron scattering opacity is known to be significant in higher layers of sun and stars, especially the hotter stars....
The operational solar wind prediction models used by the community are based on the Potential Field Source Surface (PFSS) model for the magnetic field using synoptic magnetograms. Previous studies comparing observed and modeled open magnetic flux at L1 based on PFSS extrapolations have suggested the need to optimize the source surface (SS) height with the phase of the solar cycle. The current...
Coronal mass ejections (CMEs) that cause geomagnetic disturbances on the Earth can be found in conjunction with flares, filament eruptions, or independently. Though flares and CMEs are understood as triggered by the common physical process of magnetic reconnection, the degree of association is challenging to predict. From the vector magnetic field data captured by the Helioseismic and Magnetic...
Large-scale coronal structures, such as helmet streamers (HS) and pseudo-streamers (PS), have been studied extensively as potential source regions for solar wind generation. Historically, white-light observations of the outer corona have provided insights into these features. Yet, the dynamics of HS and PS are more clearly observed in the middle corona, where the Sun’s magnetic field...
Solar flares are transient events occurring over a time scale of minutes to hours, characterized by a sudden release of magnetic energy in the form of heat and kinetic energy of the plasma. These events are believed to be the manifestations of the magnetic reconnection process. We have explored the effects of 3D reconnection in solar flares, focusing on (a) magnetofluid dynamics from the...
This study investigates the origins, characteristics, and impacts of Geo-effective Coronal Mass Ejections (CMEs) on Earth's space environment during Solar Cycle 24 th (2009-2019),with a focus on their contribution to space weather phenomena. Specifically, we examine Interplanetary Coronal Mass Ejections (ICMEs) detected at the first Lagrangian point (L1),using their key features such as...
The whole heliosphere is permeated by the solar wind. An important aspect of the solar wind is the suprathermal ion tail which is manifested in the form of particles in the energy range of a few keV/nucleon to several hundreds of keV/nucleon. In addition to the suprathermal ions, there are energetic ions having energy range exceeding 1 MeV/nucleon which are termed as solar energetic particles...
Magnetosonic waves and magnetic reconnection have been studied for a long time as two major processes responsible for coronal heating, solar wind acceleration, and other energetic eruptive processes in the Sun’s corona. Here, we study the mutual interactions between these two plasma processes in a physics-based numerical model. In this model, a velocity perturbation representing the effect of...
Sunspots, dark features on the Sun’s surface, consist of a central, darker umbra and a surrounding, less dark, filamentary region called the penumbra. Their penumbra to umbra area size ratio is crucial for understanding sunspot radiation and its contribution to total solar irradiance. This study explores this penumbra-to-umbra area ratio (q) for sunspots across solar cycles 21 to 24...
We investigate the temperature distribution for Alfvénic and non-Alfvénic regions in Interplanetary Coronal Mass Ejections (ICMEs). Our analysis reveals that approximately 63% of the ICME magnetic cloud regions are non-Alfvénic, while 37% exhibit Alfvénic characteristics, predominantly outward fluctuations. We observe significant temperature enhancements in Alfvénic regions, with the most...
We studied the sun’s chromosphere through Ca-K and H-alpha full-disk spectroheliograms from Kodaikanal archival data. Our study looks at the long-term correlation analysis of features such as plages, filaments, and active regions across these two chromospheric lines. By developing robust methodologies for feature extraction, we have tried to understand the long-term behavior of the...
We observe non-thermal radio emission with spectral indices ranging from 1 to 3, extending over megaparsec scales almost in the centre of the galaxy clusters containing largely collisionless plasma. To explain this, the electrons must be energized. While turbulence or shocks generated by merger events can accelerate electrons, their efficiency is relatively low. We explore an alternative...
Heating in the solar atmosphere has been a long standing problem in solar physics. Despite advancements in both observational and theoretical frameworks, the precise mechanisms that heat the corona are not yet well understood. Phenomena like magnetic reconnection and wave heating have been suggested as the cause, but the extent to which each process contributes to the overall...
A study of the long-term modulation of galactic cosmic rays in positive and negative phases of the 22-year solar magnetic cycle, including a period of anomalously low solar activity between 2008 and 2020 is performed. Solar magnetic field lines reconnect with galactic ones in the negative phases. In the positive phases, there is a magnetic barrier between these fields that must be considered...
We analyzed the inverse Evershed flow (IEF) around a sunspot (NOAA 13131) using line scan observations in the Fe I 6173 A and Ca II 8542 A lines. The line scan observations were acquired using a narrow band imager of the Multi-Aplication Solar Telescope (MAST), Udaipur, and were complimented with the data products of HMI onboard SDO. The line-of-sight velocities for different layers of the...
The toroidal to poloidal part of the solar dynamo mechanism involves some nonlinearity and stochasticity, which disturb the dynamo loop. Hence, the memory of the polar field decreases in every cycle. On the other hand, the dynamo efficiency and, thus, the supercriticality of the dynamo decreases with the Sun's age. Previous studies indicate that the memory of the polar field...
Various configurations of the magnetic field in the solar atmosphere effectively link plasma processes between the photosphere, chromosphere, and solar corona. In a majority of cases, these magnetic configurations are twisted. Therefore, studying excitation and propagation of magnetohydrodynamic waves in the magnetic flux tubes when twist is present is a key to understanding energy transport...
Kodaikanal solar observatory white light image data is used to explore the possible variation of sun's radius with respect to latitude. For the year 1904, very good calibrated digitized and limb darkening removed image is used. After unambiguously detected solar edge, circle is fitted, mean radius and central coordinates are estimated. By knowing these important parameters, heliographic...
Spicules have often been proposed as substantial contributors toward the mass and energy balance of the solar corona. While their transition region (TR) counterpart has unequivocally been established over the past decade or so, the observations concerning the coronal contribution of spicules have often been contested. This is mainly attributed to the lack of adequate coordinated observations,...
Helioseismic inferences show that sun's rotational gradient increases and is positive from base of convection zone to 0.935 radius of the sun. Whereas near surface (from 0.935 to 1.0 sun's radius) rotational gradient is decreasing and is negative. First question arises why present day sun adopted two regions of positive and negative rotational gradients. Hence, any theoretical work should not...
Parker Solar Probe has been trailblazing around the Sun for nearly half a solar cycle, delivering groundbreaking insights into its immediate atmosphere. To date, Parker has completed 21 of its scheduled 24 orbits during the prime science phase of the mission. The diverse and unparalleled quality data it gathers has captivated both the international space science community and the public. With...
The solar dynamo, believed to operate near the base of the convection zone (BCZ), generates the magnetic fields responsible for solar activity and solar cycles. Magnetic structures (flux tubes) formed near BCZ rise through the convection zone, potentially fragmenting/branching into smaller structures. These structures emerge as sunspots or active regions/sunspot groups on the Sun's surface....
Pi2 pulsations are impulsive oscillations associated with magnetospheric substorm onsets. In this study, we investigate a geomagnetic Pi2 pulsation using the electric field data from the Van Allen Probe satellites (NASA’ mission) in the magnetosphere, and on the ground. The Pi2 oscillations in the compressional components are investigated. We noticed a high degree of similarity between the Pi2...
Magnetic flux tubes in the presence of background rotational flows are abundant throughout the solar atmosphere and may act as conduits for MHD waves to transport magnetic energy throughout the solar atmosphere. We investigate the Poynting flux associated with these waves within the presence of background rotational plasma flows. The MHD wave solutions of the equilibrium configuration are...
Coronal fan loops rooted in sunspot umbra constantly show 3-min period propagating slow magnetoacoustic waves (SMAWs) in the corona. However, the origin of these waves in the lower atmosphere is still unclear. Here, we present study of these waves along a clean fan loop system using the multi-wavelength imaging and spectroscopic observations from IRIS and SDO. We traced the origin of these...
Solar atmosphere provides conducive environment for the generation, propagation, and dissipation of various mechanical waves. These waves are considered to play an important role in the heating and dynamics of the solar atmosphere. Acoustic waves are generated by turbulent convection inside the convection zone of the Sun. These waves trapped inside the acoustic cavities are formed due to high...
Temporary perturbations in the Earth’s magnetosphere and upper atmosphere driven by coronal mass ejections (CME) are called geomagnetic storms. It is important to understand the solar sources of geomagnetic storms in order to constrain physical drivers of space weather. A severe geomagnetic storm was observed during 10-11 May 2024. It was the strongest storm on record in the last two decades...
Radial velocity measuring instruments are nearing the precision needed for detecting Earth-like exoplanets, yet a new challenge emerges the star's own fluctuations. Disentangling the signatures of spurious radial velocity changes because of photospheric fluid flows is a complicated, multidimensional problem. Traditional methods, though partly successful, haven't fully tapped into the...
Quasi-periodic oscillations (QPOs) observed in the solar chromosphere and transition region during flares offer valuable insights into the atmospheric response to sudden energy releases and the evolution of the magnetic field. We analyzed an M-6.5 class flare observed by the Interface Region Imaging Spectrograph (IRIS), emphasizing QPOs in the Doppler velocity measured in the Si IV line at the...
We present two case studies on solar energetic particle (SEP) events involving type III storms and type II bursts in metric and decmetric-hectometre (DH) wavelengths. In one case, a type III storm was disrupted by an eruption, while in the other, the storm remained unaffected. Both events featured fast and wide coronal mass ejections (CMEs) and regular type III bursts. Analysing Nancay...
When distant radio point sources are observed through the foreground solar corona or solar wind, they experience angular or scatter broadening, and lead to change in peak flux density, anisotropy, and orientation of the major axis of the source. Such modulations are useful for probing solar wind parameters such as the amplitude of turbulence, density modulation index, proton heating rates, and...
We investigate the reformation of a quiescent filament and its structural and physical properties over two Carrington rotations. Utilizing intensity and magnetic field observations from various ground-based and space-based observatories, we continuously tracked the filament's evolution throughout the observation period. Our analysis reveals that the filament reformed in the same region twice...
The Solar Ultraviolet Imaging Telescope (SUIT) onboard Aditya-L1 performs spatially resolved full-disk imaging of the Sun across the 200–400 nm wavelength range with eleven bandpasses. SUIT provides a comprehensive view of different layers of the solar atmosphere, enabling the study of dynamic solar phenomena such as flares and jets, magnetic structures like plages, active regions, and network...
A Coronal Mass Ejection (CME) is a large-scale eruption of plasma and magnetic fields from the Sun into interplanetary space. In coronagraph observations, around one-third of CMEs exhibit a characteristic three-part structure consisting of a bright inner core, an outer leading edge, and a darker cavity in the middle. However, observations of the inner corona suggest this three-part structure...
Temporal and spatial variations in solar rotation with accurate determination and its correlation with solar activities are interesting topic in solar physics since earlier. Solar rotation can be measured by tracking the tracers across the solar disk, or via spectroscopy, or via flux modulation method using radio waves, X-rays, and UV rays that emitted out in the space. Solar Dynamics...
The CaII H and K resonance lines are widely used to study the solar chromospheric structures and their variability. These lines are very sensitive to the variations in temperature and the magnetic field strength, therefore they are excellent indicators of the chromospheric structural changes related to solar magnetic activity. The studies on the lower chromospheric variability using H-alpha...
Solar differential rotation plays an important role in the generation of Sun’s magnetic fields and its activities. For the present work, the digitized data of four chromospheric features viz plage area, enhanced network (EN), active network (AN), and quiet network (QN) obtained from Kodaikanal Observatory for the period 1907-1996 are used to investigate the differential rotation at different...
The coronal magnetic field (B) is predominant in forming structures such as streamers, holes, etc., and in determining their spatio-temporal evolution. Its routine estimation will most likely provide clues/answers to several unsolved problems in solar physics and, therefore, gain significance among solar physicists. Extrapolating the Photospheric magnetic field strength using the Potential...
The tilts of bipolar magnetic regions are believed to be caused by the action of Coriolis force on rising magnetic flux tubes. Here we analysed the combined Greenwich and Debrecen observatories sunspot-group data during the period 1874-2017 and the tilt angles of sunspot groups measured at Mt. Wilson Observatory during the period 1917 1986 and Debrecen Observatory during the period 1994-2013....
It is important to study the variabilities of solar EUV, UV and X-ray irradiance in heliophysics, in Earths climate, and space weather applications. Since the radiative output of the Sun is one of the main driving forces of the terrestrial atmosphere and climate system, the study of solar energy has become of great interest and importance. Although the solar energy flux integrated over the...
Ground-based telescopes have an inherent inability to attain diffraction-limited imaging due to the presence of the earth’s atmospheric turbulence. Speckle imaging technique helps to achieve diffraction-limited imaging by post-processing a series of short exposure imaging. In this poster, we report ongoing work of obtaining high-resolution (sub-arc seconds) images of solar surface features...
Space weather forecasts are of utmost importance in safeguarding navigation, communication, and electric power system operations, satellites from orbital drag, and the astronauts in the International Space Station from hazardous space radiation during extreme space weather conditions. The finest space weather prediction requires a clear understanding of solar wind-magnetosphere coupling. The...
Exploration of solar radio dynamic spectrum provides us with an opportunity to probe the multi-scale energetic phenomena during coronal transients including large-scale eruptions. To monitor solar radio bursts at metric wavelengths, the Udaipur Solar Observatory, Physical Research Laboratory (USO-PRL) operates a low-cost solar radio observation facility based on CALLISTO spectrometers. In this...
Solar wind interaction with the planetary magnetic field (or a conducting ionosphere), results in the formation of a magnetosphere which may be intrinsic or induced, depending upon whether the planet has its own magnetic field or not. Plasma waves are the means through which different subsystems of the magnetosphere like the magnetopause, ionopause, plasmasphere, etc. interact with each other,...
Coronal dimmings on the Sun are transient reductions in coronal plasma emissions, often associated with Coronal Mass Ejections (CMEs) triggered by solar flares or filament eruptions. These dimmings typically last between 3 to 12 hours, characterized by a rapid decrease in intensity followed by a gradual recovery. In this study, we conduct a differential emission measure (DEM) analysis using a...
We analyse chromospheric observations of NOAA AR 12765, which were acquired using a narrow-band imaging spectrometer installed with the 50-cm MAST at the Udaipur Solar Observatory. The active region included a large plage region in the vicinity of a sunspot, and we employed the NICOLE inversion code to determine 2D maps of temperature and velocity as a function of height. Photospheric vector...
The "Equal-Contrast technique" (ECT) methodology is developed to generate uniform long time series of Ca-K images obtained during the 20th century from the Kodaikanal Observatory (KO), India for studying the long- and short-term variations in the solar chromosphere. We investigate temporal and periodic variations of the fractional Ca-K plage area time series of the full solar disk for cycle 14...
Heliospheric exploration has soared to unprecedented heights in recent decades thanks to innovative spaceborne missions, ground-based observatories, and advancements in computing, models, and theory. However, the progress of inner-heliospheric research is hindered by observing limitations, preventing resolving long-standing problems such as understanding the solar dynamo, solar cycle, solar...
Spicules are thin, elongated jet-like features ubiquitously seen shooting upwards in observations of the solar atmosphere, appearing to protrude into the corona before (mostly) falling back to the solar surface. These features exhibit highly complex dynamics during their short lifetimes of 5-10 minutes and seem to be a necessary connecting link between the cooler, denser solar chromosphere and...
In May 2024, a series of solar eruptions occurred, triggered by a complex active region (β γδ ), leading to the extreme geomagnetic storm on May 10, 2024, the strongest storm in the last two decades. We investigate the kinematic and thermal evolution of coronal mass ejections (CMEs) responsible for this extreme event using multi-point coronagraphic data and near-Earth in-situ measurements,...
Extending the record of solar activity is very important to improving our understanding of the origins and evolution of solar magnetism. To this end, we attempt to generate solar magnetograms using the valuable century-long Ca II K image database from the Kodaikanal Solar Observatory (KSO). We set up an image-to-image translation model using conditional Generative Adversarial Network (cGAN) to...
Scattering polarization in strong resonance lines such as the Ca I 4227 Å, formed in the chromosphere, can probe the chromospheric magnetic fields via the Hanle effect. Predominantly one-dimensional (1D) semi-empirical model atmospheres were used to study the linear polarization in this line. Recently, Harsh et al. (2024) studied the resonance scattering polarization in Ca I 4227 Å using...
The Perseverance Rover has been on the Martian surface since February 2021. The rover has Mastcam-Z navigation stereo cameras (Kinch et al., 2020) that can capture direct images of the Sun’s surface. During periods of Mars’s orbit, the rover has a unique view-point of the Sun’s far-side (not visible from Earth at any given time). Solar scientists can use the rover’s conveniently positioned...
