Sun, Space Weather, and Solar-Stellar ConnectionSolar physics Conference

Jan 20, 2025, 8:00 AM → Jan 24, 2025, 8:30 PM Asia/Kolkata

To commemorate 125 years of Kodaikanal Solar Observatory (KSO), the Indian Institute of Astrophysics is pleased to organize an international conference on "Sun, Space Weather and Solar-Stellar Connections".  We aim to get together with the international community of researchers to discuss progress in our understanding of solar magnetism and its variability over diverse spatial, temporal, and energy scales, especially related to observations that have been carried out at this historic observatory and of the underlying fundamental physical processes that connect it to other stars. We will also survey progress in our understanding of processes manifesting as space weather that controls the near-Earth environment and those behind radio emissions from the solar chromosphere to 1 AU and their wider relevance for star-planet interactions. 

 

Tracing its origins to the late 19th century, with John Evershed's groundbreaking spectroscopic exploration of sunspots leading to his 1909 discovery of penumbral mass flows bearing his name, KSO stands nestled in a rich legacy of solar astronomical exploration. Digitization of century old archives of daily full-disk white light and Ca II-K photographic plates recorded at KSO was carried out in the last decade providing us with invaluable data to explore the long-term variability of the Sun. Such legacy data cross-calibrated and continued with observations using modern instruments hold promise of further discoveries on the behavior of magnetic fields inside the Sun.

 

We invite you to mark your calendars for this milestone conference that will serve as an effective platform for scientific discourse, merging historical records with modern cutting edge observations from the ground as well as space and theoretical/computational studies to uncover the secrets of our Sun.

 

List of Invited Speakers

 

Important dates

 

• Registration and abstract submission open  - 15 August 2024
• Deadline for abstract submission  - 07 October 2024  20 October 2024 
• Notification of abstract selection - 10 November 2024
• Deadline for registration - 01 November 2024   30 November 2024
• Announcement of the program - 15 December 2024

     Conference Dates: 20 - 24 January 2025

Registration Fee

Participants from India

• Regular - 12000 INR
• Student - 6000 INR

 

Participants from other countries

• Regular - 150 USD
• Student - 75 USD

 

 

book-of-abstracts.pdf

KSO-125_Conference_Inaugural_Session_20Jan2025_0900-0955hrs.pdf

kso125_SSW&SSC_sci_program.pdf

Poster_Conf_KSO125.pdf

PoSH Handbook_on_Sexual_Harassment_of_Women_at_Workplace.pdf

Monday, January 20

Inaugural Session

Long Term Synoptic Observations

1 Unveiling the Significance of Ca II K Observations for Long-Term Solar Irradiance Reconstructions

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 on both sunspots and faculae. Although sunspot observations readily exist back to early 1600s, facular data are significantly more scarce. The longest available record of facular data is Ca II K observations, dating back to 1892, with one of the most prominent such Ca II K archives being from Kodaikanal observatory. Unfortunately, the use of Ca II K data for irradiance studies has been hampered by significant challenges with analysing the Ca II K images, including the non-linear response of photographic plates and the presence of large-scale artifacts in the images. Our analysis of Ca II K data has allowed us to overcome many of these obstacles. We also reassessed the link between Ca II K brightness and magnetic field strength, enabling the conversion of Ca II K observations into detailed maps of the solar surface magnetic field. Here we will present our latest advancements in utilizing Ca II K data to reconstruct past solar irradiance variations.

Speaker: Theodosios Chatzistergos (Max Planck institute for solar system research)

2 Revisiting Sunspot Groups Tilt Angle Study from Kodaikanal Data

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 to the generation and evolution of large-scale solar magnetic fields.
Using daily sunspot group data from the Kodaikanal Solar Observatory for the period 1954-2017, we have studied the statistical properties of sunspot tilt angles. Key findings such as the distribution of sunspot groups tilt angles in both solar hemispheres, their variation with latitude etc. will be presented providing a comprehensive view of how tilt angles evolve over multiple solar cycles.

Speaker: Manjunath Hegde (Indian Institute of Astrophysics)

3 Characteristics of Supergranulation Network from Kodaikanal Archival Data

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 data. We studied the spatial and temporal variations of these parameters which give important information on the flux transport on the solar surface. Also, the lane widths and intensities are found to be dependent on the sunspot cycle. The correlation between lane widths and sunspot number is used as a prediction tool for the latter. The results have implications for solar dynamo models and space weather predictions.

Speaker: Raju K P (Indian Institute of Astrophysics)

4 Exploring Solar Magnetism Over Long Time Scales with Regular Full-Disc Observations

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 synoptic full-disc solar observations and of their exploitation in time, followed by a summary of the main results on solar magnetism derived with such data.

Speaker: Ilaria Ermolli (INAF Osservatorio Astronomico di Roma)

Poster Session-I / Coffee Break

Solar Interior Dynamics

5 Helioseismology with Inertial Modes

TBA

Speaker: Laurent Gizon

6 A Unified Family of Mixed Inertial Modes in the Sun

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 overtones may correspond to many of the inertial modes that have been recently identified by numerical eigenmode solvers. I will also discuss some properties of the mixed modes in the context of this model.

Speaker: Rekha Jain (University of Sheffield)

7 Inertial Waves in the Solar Convection Zone

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 modeled but not observed. Here, we present a 3D numerical simulation in spherical geometry that models the Sun’s convection zone and upper radiative interior. This model features many of these inertial oscillations and will provide a good overview of the current landscape. We additionally demonstrate that every inertial oscillation present in the model that is not a classical Rossby wave is part of the same family of mixed modes, greatly simplifying the theoretical picture.

Speaker: Catherine Blume (University of Colorado Boulder)

8 Reconciling Helioseismic Measurements of Solar Deep Meridional Flow from SDO/HMI and GONG Observations

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 and GONG data. We conduct a comprehensive comparison across different methods, data sources, and data preparation procedures, and analyze the multiple systematic effects in measurements by HMI and GONG. A systematic GONG-HMI offset in the North-South direction is confirmed. No discrepancies are found among independent measurements by multiple authors. After correcting for known systematic effects, the meridional-flow signals are consistent between GONG and HMI.

Speaker: Ruizhu Chen (Stanford University)

1:00 PM Lunch

Dynamo Models and Observations

9 Nonlinearities, Stochasticity, and Long-Term Modulations in Solar and Stellar Dynamos

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 nonlinear backreaction on inductive flows regulating the amplitude of magnetic cycles, or on the mechanism(s) driving long-term cyclic variability, including both quasi-periodic amplitude modulationand aperiodically recurring "Grand Minima" in activity. In this talk I will discuss results from non-kinematic mean-field-like dynamo simulations exploring the interaction between different nonlinear magnetic backreaction mechanisms acting concurrently, in the presence or absence of stochastic forcing. My presentation will be in the form of "vignettes" illustrating a number of interesting and often counter-intuitive effects of jointly acting nonlinearities, including (1) cycle amplitude regulation and modulation, (2) chaos and its suppression, and (3) stochastic amplification of deterministic long-term modulations.

Speaker: Paul Charbonneau (Université de Montréal, Canada)

10 Deep Cyclic Activity and Radial Flux Transport in the Sun by Assimilating Observed Magnetogram in a 3D Dynamo Model

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 that drive the solar magnetic cycle, detailing how toroidal and poloidal magnetic fields regenerate through differential rotation and sunspot decay. In our research, we are the first to incorporate daily magnetogram data into the 3D Babcock-Leighton model. We use a modified data assimilation technique akin to the Advective Flux Transport model. This approach allows us to generate cyclic variations in the toroidal field and investigate the role of internal dynamics in the solar magnetic cycle and polar fields. Additionally, by integrating insights from the SFT model, we also constrain the radial turbulent transport parameters. Our findings will be presented in detail.

Speaker: Soumyadeep Chatterjee (IIT Kanpur)

11 Surmounting the Solar Grand Minima: A Quantification of the Polar Flux Threshold

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 that the solar polar fields reach a minimum during such episodes, with a temporary halt in the polar field reversal. Eventually, with the accumulation of sufficient polar fluxes, the polarity reversal resumes, revitalizing regular sunspot cycles. Using multi-millennial dynamo simulations, we quantify the threshold of polar flux necessary to restart the polarity reversal and surmount the grand minimum phase. We also find that the duration of a grand minimum is independent of the onset rate and does not affect the recovery rate. These results may help forecast the Sun's recovery once it enters a grand minimum.

Speaker: Chitradeep Saha (CESSI, IISER Kolkata)

12 Observational Constraints for Dynamo Modeling & Active Region Flux Emergence Patterns

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. Locations where active regions repeatedly emerge are known as nests, of interest because they commonly host flares and CMEs but also because they inform us about the origins of sunspots. Why do ARs cluster spatially to form nests and is the bursty activity observed in quasi-biennial oscillations and Rieger periodicities related to nesting? The physical mechanism that causes nests is unknown but could be due to instabilities acting on the interior magnetic field or flow fields such as giant convection or inertial modes. We report on activity nests observed during Solar Cycle 24 as studied using HMI/SDO magnetic synoptic maps. Using a traditional definition of nests and searching the data with a narrow range of allowed rotation rates similar to the Carrington rate, we find that one-quarter of ARs and one-third of AR magnetic flux participate in nesting behavior. Using wavelet and Fourier analysis, we find hemispheric asymmetry in nesting behavior. We discuss these issues as well as report on the average characteristics such as lifetimes, rotation rates and amount of magnetic flux contained in the observed nests.

Speaker: Aimee Norton (Stanford University)

13 Statistical Properties of Solar Active Region Potential Magnetic Fields

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 for about 900 snapshots of active regions observed by SDO/HMI (CEA SHARP series) during solar cycle 24. We found that the magnetic energy follows a power law of the total unsigned photospheric flux with an index of about 1.5. We show the relationship (or lack of) between the activity solar cycle and the magnetic energy. We also provide a statistical distribution of the decay index during the solar cycle: the magnetic field strength is decaying differently (e-folding) depending on the properties of photospheric magnetic field (i.e., imbalance of flux, center of mass, characteristic size) and the stage of evolution. We discuss the implications for modelling active region magnetic fields and the requirements for advanced models.

Speaker: Stephane Regnier (Northumbria University)

SRegnier_talk.pptx

Poster Session-I / Coffee Break

Solar Cycle Variations in the Interior

14 Solar Cycle Variations in the Solar Interior

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 the solar magnetic field. The solar rotation shows a distinct pattern of variation with solar cycle and this is referred to as the zonal flows. These results will be discussed.

Speaker: H. M. Antia (CEBS, Mumbai 400098)

15 Geostrophic Nature of Flows Around Active Regions and Changes in the Near-surface Shear Layer of the Sun

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 radial gradient of rotation change sign. These results, together with a reverse pattern observed
during solar minimum period, point to the geostrophic nature of large-scale flows across latitudes as primary cause of the observed depth profile of changes in rotation gradient within the NSSL. We also find that the observed changes due to active regions only marginally change the amplitude of zonal flow and hence are not likely its driving force. Close agreements between the depth profiles of changes in rotation gradient and in meridional flows measured from very different global and
local helioseismic techniques, respectively, provide an important validation for the measurement procedures, especially for the latter.

Speaker: S.P. Rajaguru (Indian Institute of Astrophysics)

16 Global Nonlinear MHD of Solar Tachocline and Implications for Surface Magnetism

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 unstable MHD Rossby waves that are longitude-dependent perturbations of the global system. Major features produced include: (i) clam-shell opening of broad toroidal fields; (ii) tipping or deformation of narrow toroidal bands; (iii) Tachocline Nonlinear Oscillations or "TNOs", most likely responsible for short-term, quasi-annual bursts of solar activity; (iv) 'teleconnections' that cross-equatorially link the two hemispheres, as well as high and low latitudes within a hemisphere; (v) formation of organized, global patterns in the toroidal bands. If active regions observed at the surface are the manifestations of magnetic flux rising from the convection-zone base to the surface, their global-scale, spatio-temporal distribution could be originating from the nonlinear MHD of the tachocline. After describing these results, we will close by discussing our recent efforts to connect the bottom tachocline dynamics with surface magnetograms.

Speaker: Mausumi Dikpati (NSF-NCAR, High Altitude Observatory)

17 Study of Bipolar Magnetic Regions Using AutoTAB: Support of Thin Flux Tube Model?

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 assess the validity of the thin flux tube model by analyzing the tracked (Hale and Anti-Hale) BMR data obtained through the Automatic Tracking Algorithm for BMRs (AutoTAB). Our observations reveal that the tracked BMRs exhibit the expected collective behaviors and the polarity separations of BMRs increase over their normalized lifetimes, supporting the assumption of the rising flux tubes from the CZ. Furthermore, we observe an increasing trend of the tilt with the flux of the BMR, suggesting that rising flux tubes associated with lower flux regions are primarily influenced by drag force and Coriolis force, while in higher flux regions, magnetic buoyancy dominates. Additionally, we observe Joy's law dependence for emerging BMRs from their first detection, indicating that at least a portion of the tilt observed in BMRs can be attributed to the Coriolis force. Finally, we observe that the lower flux regions exhibit a higher amount of fluctuations associated with their tracked tilt measurements, suggesting that they are more susceptible to turbulent convection. All these results hint towards the thin flux tube model.

Speaker: Anu Sreedevi (Indian Institute of Technology (BHU) Varanasi)

Tuesday, January 21

High Resolution Observations of Solar Magnetic Fields

18 A High Resolution View of Solar Magnetic Fields

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 are particularly hard to achieve in the chromosphere, where non-LTE conditions must be included in the modelling of spectral lines and where spectral lines are weakly sensitive to the magnetic field. In this review, I will cover a selection of recent developments in the inference techniques, the state-of-the-art in solar observations and new results from the solar community in relation to high resolution solar magnetic fields.

Speaker: Jaime de la Cruz Rodriguez (Institute for Solar Physics, Stockholm University)

talk_delacruz_bangalore.pdf

19 High-resolution Measurements of Coronal Magnetic Field in Solar Flares and Associated Phenomena

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 energy release should be associated with a decrease of the coronal magnetic energy, which implies a decrease of the magnetic field. Quantitative measurements of the evolving magnetic field strength in the corona are required to find out where exactly and at which rate this decrease takes place. The only available methodology capable of providing such measurements employs microwave imaging spectroscopy of gyrosynchrotron emission from nonthermal electrons. Here, we present and review microwave observations of several solar flares showing spatial and temporal changes in the coronal magnetic field in the flare volume including flaring loops and the cusp region. In large flares the flaring magnetic field shows a prominent decay over a large coronal volume. The typical decay rate of the magnetic field is several Gauss per second, which continues at a given location for one-two minutes. Spatially resolved maps of the nonthermal and thermal electron densities derived from the same microwave spectroscopy data set allow us to detect the very acceleration site and also produce maps of such important physical parameters as Alfven speed and plasma beta in the flare volume. Using stereoscopic observations from different vantage points, these maps are converted to 3D measurements, thus, adding earlier unavailable constraints for 3D models. We discuss implications of these new findings for understanding the solar flare phenomenon including details of the energy release, particle acceleration process, and coronal waves.

Speaker: Gregory Fleishman (Institute for Solar Physics (KIS))

20 Unravelling the Stratification of the Chromospheric Magnetic Field Using the Hα Line

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 profiles. In our recently published work, Mathur et al. 2023, using spectropolarimetric data of a pore simultaneously recorded in the Hα and Ca II 8542 Å lines we investigated the potential of Hα Stokes V profiles in determining chromospheric magnetic fields. Our findings suggested that the line core of the Hα line probes the chromospheric magnetic field. However, the previous study was limited to a small pore. In this study, using spectropolarimetric observations of an active region recorded simultaneously in the Hα and Ca II 8662 Å lines, we inferred the stratification of the chromospheric magnetic field. The sunspot exhibits multiple structures, viz., 4 umbras and a lightbridge and a region where Ca II 8662 Å line core is in emission. The Hα line core image also displays brightening in the emission region, a signature of localized heating, with the spectral profiles showing elevated line cores. Consistent with the Mathur et al. 2023, we found that the magnetic field inferred from the Hα line core is consistently smaller than that inferred from inversions of the Ca II 8662 Å line at log τ500 = −4.5, however, in contrast with Mathur et al. 2023, uncorrelated. The field strength and morphology inferred in the heating region from the inversions at log τ500 = −4.5 is comparable to that of at log τ500 = −1. There is also a good agreement with the field strengths at log τ500 = −1 with that inferred from WFA over Hα full spectral range, except in the heating region. In addition, the fields inferred in the heating region from the WFA over Hα line core and full spectral range are similar in strengths and morphology. In addition, we have also performed a theoretical study of synthesizing the polarization profiles of the Hα line in 3D. We show that the line of sight magnetic field retrived is sensitive to log τ500 = −5.7, which is at higher heights compared to the Ca II IR line. Thus, we suggest that the line core of the Hα line always probes the chromospheric magnetic field at higher heights than that probes by the Ca II IR triplet. In case of heating events, the full Hα line becomes sensitive to the chromospheric magnetic field instead of just the line core. Consequently, the Hα line spectropolarimetry is a valuable diagnostic for studying the chromosphere, especially in regions with localized heating, where the Ca II IR triplet lines probe deeper layers of the solar atmosphere.

Speaker: Harsh Mathur (Indian Institute of Astrophysics)

21 Solar Magnetic Fields Before and During Eruptions

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 statistical analyses of flare magnetism using SDO/HMI datasets and will show examples of recent data-driven MHD models of eruptive X-class flares.

Speaker: Maria Kazachenko (University of Colorado Boulder / National Solar Observatory)

22 Unveiling the Dynamics and Genesis of Small-scale Fine Structure Loops in the Lower Solar Atmosphere

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 small loops utilizing data from the Interface Region Imaging Spectrograph (IRIS), the Goode Solar Telescope (GST) at Big Bear Solar Observatory, and the Atmospheric Imaging Assembly (AIA) and the Helioseismic Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO), aiming to elucidate the underlying process behind their formation. The GST observations revealed that these loops, with lengths of ∼3.5 Mm and heights of ∼1 Mm, manifest as bright emission structures in Hα wing images, particularly prominent in the red wing. IRIS observations showcased these loops in 1330 Å slit-jaw images, with TR and chromospheric line spectra exhibiting significant enhancement and broadening above the loops, indicative of plasmoid-mediated reconnection during their formation. Additionally, we observed upward-erupting jets above these loops across various passbands. Furthermore, differential emission measurement analysis reveals an enhanced emission measure at the location of these loops, suggesting the presence of plasma exceeding 1 MK. Based on our observations, we propose that these loops and associated jets align with the minifilament eruption model. Our findings suggest a unified mechanism governing the formation of small-scale loops and jets akin to larger-scale X-ray jets.

Speaker: Annu Bura (Indian Institute of Astrophysics)

23 Magnetic Field and Plasma Diagnostics Using Infrared Spectral Lines: Forward Modeling

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), which provides multiwavelength spectroscopic and polarimetric coronal measurements. We present maps of the magnetic field and plasma parameter distribution predicted based on the Zeeman effect and the known relationship between intensity ratio and plasma density, using the synthesized Stokes parameters of the Fe XIII 10747/10798 Å line pair. We examined the accuracy of magnetic field and density diagnostics during the pre-eruption and eruption stages, respectively, with different sets of instrumental parameters such as exposure time, spatial resolution and spectral resolution. Considering that the ionization and recombination processes do not have ample time to drive the ionic populations to their equilibrium state during CME propagation, especially at the CME front, and that the MHD model assumes the condition of equilibrium ionization (EI), we also performed the non-equilibrium ionization (NEI) calculation to obtain the ionic fractions by solving time-dependent ionization equations. This allows us to achieve a more physically realistic simulation of observation and diagnosis.

Speaker: Weihang Zhang (School of Earth and Space Sciences, Peking University, Beijing 100781, People’s Republic of China)

Poster Session-I / Coffee Break

Solar Chromospheric Dynamics

24 Solar Chromospheric Dynamics

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 accompanied by advances in state-of-the-art numerical modeling of the partially ionized chromosphere, including ion-neutral interactions and multi-fluid effects, providing novel insights into the physics that drive the dynamics of the solar chromosphere. I will review how the synergy between observations and modeling is key to make advances in our understanding of this critical layer in the Sun's atmosphere. I will also discuss the impact of chromospheric dynamics on the transition region and beyond.

Speaker: Bart De Pontieu (Lockheed Martin Solar & Astrophysics Laboratory)

25 Quiet-Sun Ellerman Bombs and Their Impact on the Upper Solar Atmosphere

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 characterized by rapid variability and flame-like morphologies. While a subset of these events showed localized heating in the transition region, indicated by UV brightenings in Si IV observations from the Interface Region Imaging Spectrograph, only a small fraction of QSEBs contributed to such heating. Additionally, we found cases where QSEBs were linked to the formation of type II spicules, suggesting that magnetic reconnection could be a driving mechanism for spicules. However, these associations account for only a small portion of the total number of QSEBs and spicules, indicating that QSEBs likely play a limited role in global upper-atmosphere heating and spicule formation.

Speaker: Jayant Joshi (Indian Institute of Astrophysics)

26 Simulations of the Solar Spicule Forest - Dependence on Magnetic Field Strength and Coronal Temperature

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 the spicules (e.g., height, acceleration) depend on the properties of the magnetic environment. We also present the analysis to understand the physics behind such dependence on the magnetic field (Kesri et al, 2024, ApJ) and coronal temperature.

Speaker: Piyali Chatterjee (IIA)

27 Vortex Dynamics in Various Solar Magnetic Field Configurations

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 all three regions. We investigate kinetic and magnetic swirling strength and find them consistent with the Alfvén wave propagation. Using a flux tube expansion model and linear magnetohydrodynamics (MHD) wave theory, we find that the deviation in kinetic swirling strength from the theoretically expected value is the highest for the Strong Plage, least for the Weak Plage, and intermediate for the Quiet Sun at chromospheric heights. It suggests that Weak Plage is the most favoured region for chromospheric swirls, though they are of smaller spatial extents than in Quiet Sun. We also conjecture that vortex interactions within a single flux tube in Strong Plage lead to an energy cascade from larger to smaller vortices that further result in much lower values of kinetic swirling strength than other regions. Fourier spectra of horizontal magnetic fields at 1 Mm height also show the steep cascade from large to smaller scales for Strong Plage. These findings indicate the potential of vortex-induced torsional Alfvén waves to travel higher in the atmosphere without damping for weaker magnetic regions such as the Quiet Sun, whereas vortices would result in dissipation and heating due to the vortex interactions in narrow flux tubes for the strongly magnetized regions such as Strong Plage.

Speaker: Nitin Yadav (Indian Institute for Science Education and Research)

28 Chromospheric and Coronal Heating in Active Regions: A Joint Perspective from Observations and Numerical Simulations

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 on small spatial scales. Here we use unique coordinated observations of the chromosphere (from the IRIS satellite) and the low corona (from the Hi-C 2.1 sounding rocket), and machine-learning-based inversion techniques, to show a strong correlation on spatial scales of a few hundred kilometers between heating in the chromosphere and emission in the upper transition region in strong magnetic field regions (‘plage’). Furthermore, we follow up on this study with coordinated SST and Solar Orbiter observations that further constrain the observed heating patterns. Our observations are compatible with an advanced three-dimensional magnetohydrodynamic simulation in which the dissipation of current sheets caused by magnetic field braiding is responsible for heating the plasma simultaneously to chromospheric and coronal temperatures. Our results provide deep insight into the nature of the heating mechanism in solar active regions.

Speaker: Souvik Bose (Lockheed Martin Solar & Astrophysics Lab/SETI Institute)

29 Small-Scale Swirls in the Solar Atmosphere

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 advancements in the automated detection of solar atmospheric swirls, highlighting their role in exciting Alfvén pulses channeling energy to the upper solar atmosphere and exploring the spatial and temporal relationship between swirls and photospheric magnetic concentrations. Furthermore, our analysis reveals periodicities in swirl parameters ranging from 3 to 8 minutes, remarkably coinciding with the dominant period of the global p-mode spectrum. This suggests a potential link between global p-modes and the triggering of both photospheric and chromospheric swirls.

Speaker: Jiajia Liu (University of Science and Technology of China)

1:00 PM Lunch

Waves in the Solar Atmosphere

30 MHD Waves in the Solar Atmosphere: Recent Advances from High-resolution Observations

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, enabling the study of MHD wave phenomena in intricate detail, and revealing their diverse manifestations and crucial role in energy transport and heating. This review talk will explore the latest observational findings, highlighting the diverse nature of MHD waves. A key challenge in this field is disentangling the various MHD wave modes superimposed on each other within the same magnetic structures, a complex task due to their overlapping signatures in observational data. This talk will emphasise how the combination of advanced instrumentation, multi-wavelength observations, and sophisticated analysis techniques is crucial for the correct identification and interpretation of these different wave modes. We will discuss the implications of these observations for our understanding of chromospheric and coronal heating, providing new insights into the overall dynamics of the solar atmosphere.

Speaker: Shahin Jafarzadeh (Queen’s University Belfast, UK/Max Planck Institute for Solar System Research, Germany)

31 Investigation of Umbral Wave Dynamics in the Chromospheric Resonator through Multi-Height 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 studying sunspots. We investigate wave propagation patterns in the chromosphere of a large sunspot using high-resolution, multi-wavelength optical data from the Goode Solar Telescope (GST) at Big Bear Solar Observatory. Our analysis focuses on intensity oscillations at various points in the Hα line profile, as well as the Doppler velocity of the Hα line. By applying wavelet analysis, we identify the periodicity of these oscillations. Statistical analysis reveals a prevalent 3-minute oscillation across all Hα line measurements. To show the phase relationships between different Ha channels, we conduct phase difference analysis, estimating the phase difference between intensity in different bandpasses (such as Hα line core, Hα±0.2Å, Hα±0.4Å, Hα±0.6Å, Hα±0.8Å, and Hα±1Å) and Doppler velocity of Hα line. We found that the umbra waves exhibit a pattern of slow wave in forms of upward propagating wave, standing wave and a mixture of both. The observed phase relationships suggest that these umbral waves are confined within a non-ideal acoustic resonator.

Speaker: Kartika Sangal (IIT BHU, Varanasi)

32 Shock Wave Propagation in the Solar Atmosphere

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 investigate the formation and propagation of these shock waves in the chromosphere, examining their implications in the higher solar atmosphere using observations from the Multi Application Solar Telescope (MAST), the Swedish 1-meter Solar Telescope (SST), the Interface Region Imaging Spectrograph (IRIS), and the Solar Dynamics Observatory (SDO). Our results show that these shock waves are predominantly observed in or near magnetic flux concentration regions and can propagate atleast up to the transition region. In this talk, I will discuss the identification of these shock waves, their propagation characteristics, and their potential implications in coronal dynamics.

Speaker: Ravi Chaurasiya (UDAIPUR SOLAR OBSERVATORY/PHYSICAL RESEARCH LABORATORY)

33 Exploring Wave Coupling and Energy Dissipation in the Solar Atmosphere

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 the high-frequency part of the spectrum plays a key role in energizing the solar atmosphere. However, probing high frequencies presents challenges for both instrumentation and modeling. On the modeling side, new physical aspects, such as the interaction between neutrals and plasma, are being incorporated. In this talk, I will review recent advances in theoretical studies of high-frequency waves, shocks, and vorticity propagation through the solar atmosphere, with a focus on multi-fluid modeling of these dynamic phenomena.

Speaker: Elena Khomenko (Instituto de Astrofisica de Canarias)

34 The Properties of Propagating Compressive Waves in a Multithermal Coronal Loop

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 generate synthetic images, which reveal that the observed propagation speeds are dependent on the temperature response of the filter used. Furthermore, we find that the slow waves are damped despite the absence of any dissipation mechanism in our model. This is because of the phase differences in their propagation across different strands. We call this the Multithermal Apparent Damping (MAD). Our results indicate that MAD is as effective as thermal conduction, especially, for the short period waves.

Speaker: Krishna Prasad Sayamanthula (Aryabhatta Research Institute of Observational Sciences (ARIES))

Poster Session-I / Coffee Break

Instruments/Facilities and Science: New and Upcoming

35 Scientific Achievements Based on Data from Solar Orbiter/EUI

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 EUI range from new insights into the smallest coronal structures ever resolved in the EUV to the large-scale evolution, e.g. of CMEs, at much larger distances above the limb than what was possible before. In this short overview I will concentrate on dynamic features in the quiet Sun, coronal holes and active regions and how these might be understood with the help of (coronal) models. The comparison of models and observations gives new insight into the mass and energy supply at the base of the solar wind through small-scale jets or of the heating of small-scale brightening through magnetic reconnection processes, to name just two examples. However, there are also coronal features or properties that elude an explanation by current models. Many modern 3D models of coronal features are driven by the near-surface magneto-convection, which allows us to address the question how (small-scale) magnetic patches evolve and through this energize the upper atmosphere of the Sun. Together with observations of the photospheric magnetic field, on Solar Orbiter with the PHI instrument, this can put new constraints on our understanding of the structure, heating and dynamics of the Solar atmosphere.

Speaker: Hardi Peter (Max Planck Institute for Solar System Research (MPS), Göttingen and Institut for Solar Physics (KIS), Freiburg, Germany)

36 Aditya-L1: An Observatory Class Mission for Solar and Heliospheric Observations

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. Remote sensing payloads observe the photosphere, chromosphere, and coronal regions of the solar atmosphere. The in-situ payloads cover the electrons, protons, heavier ions along with vector magnetic field at L1. Aditya-L1 have certain unique capabilities which allow them to carryout observations which are complementary to the other space observatories. In this presentation, Aditya-L1 capabilities will be brought out.

Speaker: Sankarasubramanian Kasiviswanathan (U R Rao Satellite Centre, Indian Space Research Organization)

Aditya-L1-Science_Capabilities_Jan2025_IIAMeeting.pdf

Aditya-L1-Science_Capabilities_Jan2025_IIAMeeting.pptx

37 The Fabry-Pérot Imaging Spectropolarimeters for the European Solar Telescope

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 chromospheric magnetic fields over large fields of view. Each of these instruments consists of a narrow-band imaging spectropolarimeter and a broad-band imager. The spectropolarimeter is based on a dual Fabry-Pérot etalon system and a polarimeter incorporating two nematic liquid crystal variable retarders. The imager consists of two large-format, fast cameras to allow reconstruction of the narrow-band images by means of multi-frame blind deconvolution and phase diversity. The three TIS/FBIs will be operated in parallel for high cadence monitoring of the lower solar atmosphere in three or more spectral lines simultaneously, greatly improving the capabilities of existing filtergraphs that measure individual lines sequentially. In addition, the TIS/FBI instruments will provide unprecedented polarimetric sensitivity due to their optimized design and the large photon collecting area of the 4.2 m diameter primary mirror of EST. In this talk we will present the science goals of the EST TIS/FBI instruments. We will also review the current status of the TIS/FBIs, focusing on the main design drivers and the technological solutions adopted in this development phase. The TIS/FBIs are expected to go through a conceptual design review in 2025, together with the other instruments of the EST Instrument Suite.

Speaker: Luis Bellot Rubio (Instituto de Astrofisica de Andalucia (IAA-CSIC))

Wednesday, January 22

Jets and Magnetic Reconnection

38 Spicules and Jets in the solar Chromosphere: A Perspective of Recent Advances

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 their driver being magnetic reconnection or waves is very much still alive, and simulations of ever increasing realism provide important clues about different drivers. The coronal connection of spicules is now placed on much stronger footing thanks to detailed multi-instrument observations. Finally, thanks to modern techniques for big data we can now analyse complex spectral and imaging data and detect events on a vast scale, providing unique statistics that give us more insight into the atmospheric impact of these enigmatic phenomena.

Speaker: Tiago Pereira (University of Oslo)

Spicules KSO 2025.pdf

39 The Magnetic Origin of Solar Coronal Jets and Campfires: SDO and Solar Orbiter Observations

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 they often appear at sites of magnetic flux cancelation between the majority-polarity magnetic flux patch and a merging minority-polarity flux patch, with a flux cancelation rate of ∼1018 Mx hr−1 (ii) majority of campfires are preceded by a cool-plasma structure, analogous to minifilaments in coronal jets. Our observations suggest that (a) the presence of magnetic flux ropes may be ubiquitous in the solar atmosphere and not limited to coronal jets and larger-scale eruptions that make CMEs, and (b) magnetic flux cancelation, most likely accompanied with magnetic reconnection in the lower solar atmosphere, is the fundamental process for the formation and triggering of most solar campfires and coronal jets. Finally, we compare fine-scale jets with those found in a Bifrost MHD simulation.

Speaker: Navdeep Panesar (LMSAL/BAERI)

40 Transition Region Brightening in a Moss Region and their Relation with Lower Atmospheric Dynamics

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 dynamics, which could provide insights into the underlying generation mechanisms of the SBs. We analyzed the data sets obtained by coordinated observations using the Interface Region Imaging Spectrograph and the Goode Solar Telescope at Big Bear Solar Observatory. We studied 131 SB events in our region of interest and found that 100 showed spatial and temporal matches with the dynamics observed in the chromospheric Hα images. Among these SBs, 98 of them were associated with spicules that are observed in Hα images. Furthermore, detailed analysis revealed that one intense SB event corresponded to an Ellerman Bomb (EB), while another SB event consisted of several recurring brightenings caused by a stream of falling plasma. We observed that Hα far wings often showed flashes of strong brightening caused by the falling plasma, creating an Hα spectral profile similar to an EB. However, 31 of the 131 investigated SB events showed no noticeable spatial and temporal matches with any apparent features in Hα images. Our analysis indicated that the predominant TR SB events in moss regions are associated with chromospheric phenomena primarily caused by spicules. Most of these spicules display properties akin to dynamic fibrils.

Speaker: Tanmoy Samanta (Indian Institute of Astrophysics)

41 Small-scale Magnetic Flux Emergence Preceding a Chain of Energetic Solar Atmospheric Events

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 Solar Telescope (SST), the Interface Region Imaging Spectrograph (IRIS), and the Solar Dynamics Observatory (SDO) to analyze an ephemeral magnetic flux emergence episode and the following chain of small-scale energetic events. These unique observations clearly link these phenomena together. The high-resolution (0.057”/pixel) magnetograms obtained with SST/CRISP allowed us to reliably measure the magnetic field at the photosphere and to detect the emerging dipole that caused the subsequent eruptive atmospheric events. Notably, this small-scale emergence episode remains indiscernible in the lower resolution SDO/HMI magnetograms (0.5”/pixel). We report the appearance of a dark bubble in Ca II K 3933 Å related to the emerging dipole, a sign of the canonical expanding magnetic dome predicted in flux emergence simulations. Evidence of reconnection is also found, first through an Ellerman bomb and later by the launch of a surge next to a UV burst. The UV burst exhibits a weak EUV counterpart in the coronal SDO/AIA channels. By calculating the differential emission measure (DEM), its plasma is shown to reach a temperature beyond 1 MK and to have densities between the upper chromosphere and transition region. Our study showcases the importance of high-resolution magnetograms in revealing the mechanisms that trigger phenomena such as EBs, UV bursts, and surges. This could hold implications for small-scale events similar to those recently reported in the EUV using Solar Orbiter. The finding of temperatures beyond 1 MK in the UV burst plasma strongly suggests that we are examining analogous features. Therefore, we recommend caution when drawing conclusions from full-disk magnetograms that lack the necessary resolution to reveal their true magnetic origin.

Speaker: Daniel Nóbrega-Siverio (Instituto de Astrofísica de Canarias (IAC))

42 Campfires and Nanoflares: Signatures of Finest-scale Magnetic Reconnection in Quiet-Sun Corona Observed by Extreme Ultraviolet Imager aboard Solar Orbiter

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 elusive due to the absence of extensive statistical studies. We perform statistical analysis of the campfires by using the highest possible resolution observations obtained by the Extreme Ultraviolet Imager (EUI) onboard SolO. We use observations in the 17.4 nm passband of the High Resolution EUV Imager (HRIEUV) of EUI obtained during the closest perihelia of SolO in the years of 2022 and 2023. SolO being at a distance 0.29 AU from the Sun, these observations have exceptionally high pixel resolution of 105 km with a fast cadence of 3 seconds. We report the detection of the smallest campfires ever in the quiet-Sun. The detected campfires have sizes of 0.01 Mm$^{2}$ to 10 Mm$^{2}$. Their lifetimes vary between 3 s and 1000 s. Their distribution of size and lifetime show the power-law behaviour. We find a positive correlation between size, lifetime, and intensity of the campfires. We estimate that about 4000 campfires appear per second on the whole Sun. Considering the HRIEUV bandpass that is most sensitive to the 1 MK plasma, the increasingly high number of campfires at smaller spatial and temporal scales over the quiet-Sun regions supports the nanoflare model of solar coronal heating.

Speaker: Nancy Narang (Royal Observatory of Belgium)

43 Localized Heating and Dynamics in Coronal and Chromospheric Plasmas due to a Symbiosis of WAves and Reconnection (SWAR)

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 generate waves. We present and review our recent observations and numerical models which show how wave-like perturbations can help forming a localized current sheets in the solar atmosphere and thereby heat it. We also demonstrate how the energetics and dynamics of the large-scale corona can be influences by waves emitted from reconnecting current sheets. Furthermore, we discuss the broad implications of such a Symbiosis of WAves and Reconnection (SWAR) for chromospheric and coronal dynamics at disparate scales.

Speaker: Abhishekh Kumar Srivastava (Department of Physics, Indian Institute of Technology (BHU))

Poster Session-II / Coffee Break

Flares and CMEs

44 Origin and Energization of Solar Eruption Events

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 their origin and energization. My talk, on the one hand, will address the new discovery of pre-eruptive configurations causing solar eruptions and deliver a new understanding of how the pre-eruptive configurations evolve from the slow-rise precursor to the violent eruption. The second part of my talk will focus on observations and simulations of magnetic reconnection within the current sheet between the erupting CME and flare loops with a preference on its turbulent nature, aiming to understand the basic energy release pattern of flare reconnection and disclose the physical origins of various flare fine structures.

Speaker: Xin Cheng (Nanjing University)

45 Low Coronal Disturbances and Coronal Mass Ejections

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) images before they emerge in coronagraph images. Among them, the coronal dimming may be the most reliable indicator, which is often accompanied by a large-scale coronal propagating front (or an EUV wave as more commonly referred to). We present an ensemble study of EUV waves based on images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (there are many hundreds of events since 2010) and from the Extreme-Ultraviolet Imager (EUVI) on board the Solar-Terrestrial Relation Observatory (STEREO). The focus of this study is on the relation of EUV waves with CMEs, which are characterized in coronagraph data from SOHO and STEREO. We discuss the relative magnitude of EUV waves, dimmings and CMEs, which may vary in different phases of solar cycles. The involvement of EUV waves in CMEs may depend on the height at which the CME starts to accelerate and on the large-scale magnetic field surrounding the eruption.

Speaker: Nariaki Nitta (Lockheed Martin Advanced Technology Center)

46 Solar Jets: Insights from High-Resolution Observations and Numerical Simulations

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 (SST), in coordination with IRIS and SDO. We compared the observed jet features with a 3D numerical simulation of reconnection-driven jets performed with the ARMS code. Three significant observational signatures were identified: (1) the formation of a hook along the circular ribbon, (2) the jet’s widening through displacement of its kinked edge toward the reconnection site, and (3) the fallback of some jet plasma toward an offset footpoint. These features, which align with the 3D asymmetric reconnection geometry of swirled-anemone loops, suggest that such characteristics are common in impulsive solar jets. The generic nature of the simulation supports the hypothesis that these features are typical in similar jet events.

Speaker: Reetika Joshi (Rosseland Centre for Solar Physics)

47 Onset, Eruption, and Thermal Properties of Coronal Jets via MHD Simulation

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 a blowout jet using observations from AIA/SDO and employing the non-force-free-field (NFFF) extrapolation model. We then simulate the magnetic field evolution via EULAG-MHD model. We have compared the simulated dynamics to the observed features as well as the emission profile obtained from the differential emission measurement (DEM) analysis. We have utilized the HMI/SDO magnetogram as an input to the NFFF model. The simulation is initialized with the non-zero Lorentz force inherent to the extrapolated magnetic field with a line-tied bottom boundary condition. Interesting are the initial magnetic configurations, where we find a bald patch and a flux rope near the jetting region. The reconnections near the bald patch may trigger the onset of the jet. The untwisting of the flux rope channels the plasma material to escape. Further to supplement the study of the onset process and thermal changes, we have analyzed different parts of the jet in detail, where we find profiles of simulated current density, and energy densities (magnetic+kinetic), in congruent with the measured emissions. We have shown the role of Lorentz force in driving the jet and compared its effect over the plasma flow during the whole simulation period. In future, to understand the role of boundary in initiating such transients and the simultaneous thermal properties, we plan to carry out a complete magnetohydrodynamics study with a data-driven boundary approach aided with spectroscopic data with high-spatial and temporal cadence from instruments like IRIS, and SP/Hinode, SST.

Speaker: Sushree Sangeeta Nayak (CSPAR/UAH)

48 Small and Large Scale Episodic Events in Smaller and Larger Scale Numerical Simulations Spanning the Convection Zone to the Corona

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 dynamo, but also the emergence of larger scale magnetic structures from deeper layers is important, even in the quiet Sun. A significant proportion of this field likely reaches the chromosphere and leaves imprints on chromospheric and coronal dynamics and energetics. Using a number of numerical models, (24x24x17) and (72x72x60) Mm, the high resolution spectra and slit jaw images from IRIS, imaging data from SDO/AIA and Solar Orbiter’s EUI/HRI, as well as ground based Ca II 854.2 and Ca II spectrograms, are synthesised and compared to observed data. We also synthesise observations from the upcoming MUSE and EUVST observatories in the context of episodic heating. The magnetic structure and dynamics of small scale events such as jets and dots, more energetic Ellerman bombs and a small C-class flare are discussed and analysed.

Speaker: Viggo Hansteen (Bay Area Environmental Research Institute/Lockheed Martin Solar and Astrophysics Laboratory and RoCS/University of Oslo)

12:45 PM Lunch

Shocks and Particle Acceleration and Transport in IP Medium

49 Energetic Particle Acceleration and Transport: Interplanetary Coronal Mass Ejections and Shocks

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 multi-point, multi-instrument observations available by a fleet of spacecraft in the heliosphere. The Solar Orbiter (SolO) and Parker Solar Probe (PSP) pioneering missions have been providing unprecedented measurements of energetic particles in the near-Sun environment. In particular, we present the properties of an Interplanetary CME-driven shock and its evolution with heliocentric distance, observed on September 5, 2022 by PSP at an unprecedentedly low heliocentric distance of 0.07 au, then reaching SolO which was radially well-aligned at 0.7 au. An overview of the characteristics of the energetic particle population at each spacecraft is also discussed in relation to magnetic and plasma structures and expectations from acceleration processes. Furthermore, we present the detailed analysis of the widespread SEP event on January 20, 2022, during which the measurements of the EPD experiment onboard SolO made the unusual observation that particles first arrived from the anti-Sun direction. i.e. streaming towards the Sun. The STEREO-A and MAVEN spacecraft also observed the event suggesting that particles spread over at least 160° in the heliosphere. The aim of the study is to show how SEPs are accelerated and transported to SolO and near-Earth spacecraft as well as the examination of the influence of a magnetic cloud present in the heliosphere at the time of the event onset on the propagation of the energetic particles. An overview of interesting observations made by multiple spacecraft in the heliosphere (e.g. PSP, BepiColombo, SolO, STEREO-A) during the widespread SEP event on February 15-16, 2022, one of the most intense SEP events observed so far in solar cycle 25 is also presented. Results from analyses of the corresponding Energetic Storm Particle (ESP) event (~0.05 – 2 MeV ions) as observed by the PSP ISʘIS/EPI-Lo instrument on February 16, 2022 at 0.35 au from the Sun is also summarized and other unique observations of multi-spacecraft events.

Speaker: Olga Malandraki (National Observatory of Athens/IAASARS, Athens, Greece)

50 Connecting Energetic Electrons at the Sun and in the Heliosphere through X-ray and Radio Diagnostics

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, while downward moving electrons produce X-rays in the chromosphere, upward moving electrons may generate coherent radio emissions when propagating through the corona, such as radio type III bursts. The launch of the Solar Orbiter in early 2020 marked a significant milestone, as it is equipped with the capability to simultaneously capture both types of emission. In this contribution, we shall present the first tresults derived from the comparison of X-ray flares observed by STIX in the 4-150 keV range on Solar Orbiter with radio type III bursts detected by RPW below 10 MHz on Solar Orbiter. The study focuses on 15 Interplanetary Type III radio bursts (IT3s) associated with HXR emission peaks, observed during the second commissioning phase of the STIX from November 17 to 21, 2020. Changes in the X-ray source morphology are found coinciding with the occurrence of IT3 emissions, and combined observations with the EUI instrument suggest a delayed access to existent open magnetic field lines within the active region. In the second part of the presentation we will investigate the link between the speed of the electron beams traveling outward (deduced from radio) and the energy density of the electrons traveling downward (deduced from X-rays). Indeed, assuming both electron populations share properties from a common acceleration region, some correlations should be found between these two quantities. Higher velocities in type III bursts are thus expected to be associated with a harder electron spectrum and larger beam density, as inferred from X-ray observations, indicating a larger amount of high-energy electrons interacting with Langmuir Waves. We shall present results derived from the comparison of more than 20 flares observed by STIX and associated in time with radio type III bursts detected by RPW below 10 MHz.

Speaker: Nicole Vilmer (LIRA Paris Observatory)

51 Suprathermal Ion Observations Associated with the Heliospheric Current Sheet Crossings by Parker Solar Probe

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 crossings. We find that these unique ST observations are remarkably different in each case, with those during E07 posing the most serious challenges for existing models of ST ion production in the inner heliosphere. In contrast, the ISOIS observations during the remaining HCS crossings appear to be consistent with a scenario in which ST ions escape out of the reconnection exhausts into the separatrix layers after getting accelerated up to ~50-100 keV/nucleon by HCS-associated magnetic reconnection-driven processes. We discuss these new observations in terms of local versus remote acceleration sources as well as in terms of expectations of existing ST ion production and propagation, including reconnection-driven and diffusive acceleration in the inner heliosphere.

Speaker: Mihir Desai (Southwest Research Institute)

52 Time Evolution of Thermal and Non-Thermal Energies in Solar Flares

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 Imaging X-rays (STIX). By utilizing these datasets, we estimate the total thermal energy for both flares by calculating the Differential Emission Measure (DEM) to track changes in thermal energy over time. For the X-class flare, we further incorporate spectra from STIX on the Solar Orbiter to estimate the non-thermal energy component. Additionally, we examine how evolving volume estimates of the flare structure affect our thermal energy calculations, highlighting the value of high-resolution imaging from multiple wavelengths and perspectives. We propose a method to accurately determine the Line of Sight (LOS) throughout the Field of View (FOV) by using near-simultaneous observations from different vantage points, leading to a more precise volume estimate of the flare arcade. For the M-class event, we also analyze the thermal structure of the fan compared to the overall thermal evolution of the flare, finding that the thermal energy decay in the fan is slower than in the flare loops, which suggests a unique heating mechanism within the fan structure.

Speaker: Soumya Roy (IUCAA, Pune)

Poster Session-II / Coffee Break

Instruments/Facilities and Science: New and Upcoming

53 National Large Solar Telescope (NLST) of India

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 Himalayas, situated above 4,000 meters. These sites offer exceptionally low water vapor content and are shielded from monsoon disruptions, providing ideal conditions for solar observations. The NLST's innovative optical design employs an on-axis Gregorian configuration with a minimal number of optical elements. This reduces the number of reflections, enhancing throughput and minimizing polarization effects. Furthermore, the telescope incorporates high-order adaptive optics to achieve near-diffraction-limited imaging, compensating for atmospheric turbulence. To mitigate atmospheric and thermal disturbances, the NLST will operate with a fully open dome, maximizing its capabilities. The telescope will be mounted on a 20-meter tall tower, providing additional stability and isolation from ground-based disturbances. The NLST's post-focus instrumentation suite includes a range of advanced devices, such as broad-band and tunable Fabry-Perot narrow-band imagers, and a high-resolution spectropolarimeter. Led by the Indian Institute of Astrophysics and supported by domestic and international collaborators, the National Large Solar Telescope (NLST) project will significantly advance our understanding of the Sun. Strategically located in Asia, the NLST will complement existing solar observatories in the United States and Europe, providing valuable new insights into our nearest star.

Speaker: Ravindra B (IIA, Bangalore)

54 Performance of the Upgraded GRIS@GREGOR Spectrograph

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 long-slit and IFU modes available to the observers. More recently, two additional spectroscopic channels have been added to make feasible simultaneous spectroscopic observations in three spectral intervals. The second channel has already been implemented, tested and commissioned during 2024, with simultaneous observations obtained in two wavelengths (mainly centered in Ca II 854 nm and He 1083 nm, but not exclusively). In this talk, the performance of the dual channel configuration will be described, presenting actual data obtained during the commissioning phase.

Speaker: Manuel Collados (Instituto de Astrofísica de Canarias)

55 Solar Orbiter/EUI Observations and a Bifrost MHD Simulaton of Fine-scale Dot-like Heating Events in Emerging Flux Regions

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, and an intensity enhancement of 30\% $\pm$10\% from their immediate surroundings. About half of the dots remain isolated during their evolution and move randomly and slowly ($<$10 \kms). The other half show extensions, appearing as a small loop or surge/jet, with intensity propagations below 30\,\kms. Many of the bigger and brighter \hri\ dots are discernible in SDO/AIA 171 \AA\ channel, have significant EM in the temperature range of 1--2 MK, and are often located at polarity inversion lines observed in HMI LOS magnetograms. The Bifrost MHD simulations of an emerging flux region do show dots in synthetic \fe\ images, although dots in simulations are not as pervasive as in observations. The dots in simulations show distinct Doppler signatures -- blueshifts and redshifts coexist, or a redshift of the order of 10 \kms\ is followed by a blueshift of similar or higher magnitude. The synthetic images of \oxy\ and \siiv\ lines, which form in the transition region, also show the dots that are observed in \fe\ images, often expanded in size, or extended as a loop, and always with stronger Doppler velocities (up to 100 \kms) than that in \fe\ lines. Our results, together with the field geometry of dots in the simulations, suggest that most dots in emerging flux regions form in the lower solar atmosphere (at $\approx$1 Mm) by magnetic reconnection between emerging and pre-existing/emerged magnetic field. The dots are smaller in \fe\ images (than in \oxy, and \siiv\ lines) most likely because only the hottest counterpart of the magnetic reconnection events is visible in the hotter emission. Some of these dot-like heating events might be manifestations of magneto-acoustic shocks (driven from the lower atmosphere) through the line formation region of \fe\ emission. Because these fine-scale heating events carry magnetic energy of the order of 10$^{26}$ erg, they contribute significantly to a CBP's heating, and mark where exactly the heating happens within CBPs.

Speaker: Sanjiv Tiwari (Lockheed Martin Solar & Astrophysics Laboratory & Bay Area Environmental Research Institute, CA, USA)

56 The Gauribidanur Radio Observatory: Current Status and Future Plans

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 simultaneously images the Sun at two spot frequencies, viz., 53 and 80 MHz, during its local meridian transit; the spatial resolution at 80 MHz is 4′×7′(RA×Dec.), and the image-dynamic range is ≈22 dB. The GLOSS observes the Sun as a point source and produces the solar radio dynamic spectrum in 50-500 MHz over 2:30-10:30 UT. The frequency resolution and the dynamic range of a dynamic spectrum are ≈500 kHz and 40 dB, respectively. The GRIP observes the polarized radio emission from the Sun in 30-130 MHz over 2:30-10:30 UT. The dynamic range of the total and circularly polarized flux profiles is ≈30 dB and has a spectral resolution of about 1.5 MHz. The GRASP observes the Sun as a point source and produces the dynamic spectra of the total and circularly polarized flux in the 15-35 MHz during 2:30-10:30 UT. The spectra have a dynamic range of ≈30 dB and a spectral resolution of 2 kHz. Apart from the solar facilities, we have recently established a new small array to observe the non-solar radio transients, the Pulsars, FRBs, etc. The talk will briefly cover the observing facilities, highlight the results, the ongoing facility upgrade, and the plans for the future.

Speaker: Kathiravan Chidambaram (Indian Institute of Astrophysics)

57 Investigations on Suprathermal Ions Observed by ASPEX/STEPS on board Aditya-L1 During its Earth-Bound Orbits

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 to numerous particle detectors on board various spacecraft. Recently launched India’s Aditya-L1 includes the SupraThermal Energetic Particle Spectrometer (STEPS), a subsystem of the Aditya Solar wind Particle EXperiment (ASPEX) suite, which can measure suprathermal and high energetic ions from multiple directions. After the launch on 02 September 2023, the Aditya-L1 spacecraft completed several highly elliptical earth-bound orbits before it started cruising towards the halo orbit around the L1 point on 19 September 2023. Two detector units, Parker Spiral (PS) and North Pointed (NP), were the first to start measurements from 10 September 2023 onwards whenever the altitude of the spacecraft crossed ~ 52000 km. During 10 – 18 September 2023, STEPS units sampled suprathermal ions from the Earth’s magnetosphere, magnetosheath, and IP medium. Coincidentally, three ICMEs hit the Earth during the above interval. The results from this interesting observation will be discussed in this presentation.

Speaker: Bijoy Dalal (Physical Research Laboratory, Ahmedabad, India)

Thursday, January 23

The Sun as a Prototype of Stellar Variability

58 The Sun as a Proxy for Stellar Variability

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 planet-hunting missions CoRoT and Kepler initiated a new era in examining the magnetically-driven brightness variations of stars. Such brightness variations, on both the rotational timescale, but also on the timescales of decades, are well studied and understood for the Sun. The plethora of data available now allows to accurately compare solar and stellar brightness variations. An intriguing question is whether the observed trends in the stellar photometric variability can be explained by utilising the solar paradigm, in particular the physical concepts of brightness variations learnt from the Sun. In this talk, I will present recent efforts of modelling stellar variability by following the path of extending the solar paradigm (e.g. the physical mechanisms causing solar variability) to stars with higher activity and rotation rates.

Speaker: Nina-Elisabeth Nemec (CSIC-ICE)

IIAP_Nemec_talk.pdf

59 The Role of Meridional Flow in the Generation of Solar/Stellar Magnetic Fields and Cycles

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 generating magnetic fields in Sun and sun-like stars using STABLE [Surface flux Transport And Babcock–LEighton] dynamo model. We find that a moderate meridional flow increases the polar field by efficiently driving the trailing polarity flux toward the pole. In contrast, a strong flow tends to transport both polarities of BMRs poleward, potentially reducing the polar field. Our findings agree with what one can expect from the surface flux transport model. Similarly, the toroidal field initially increases with moderate flow speeds and then decreases after a certain value. This trend is due to the competitive effects of shearing and diffusion. Furthermore, our study highlights the impact of meridional flow on the cycle strength and duration in stellar cycles. By including the meridional flow from a mean-field hydrodynamics model in STABLE, we show that the magnetic field strength initially increases with the stellar rotation rate and then declines in rapidly rotating stars, explaining the observed variation of the stellar magnetic field with rotation rate.

Speaker: Vindya Vashishth (Indian Institute of Technology (BHU) Varanasi)

60 Dynamics of Photospheric Magnetic Flux Distribution and Variations in Solar RVs: A Study Using HARPS-N Solar and SDO Observations

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 searches. In this work, we employ high resolution images of the solar magnetic field and continuum intensities from SDO/HMI to understand the activity contributions to RVs from HARPS-N solar observations. Using well-observed physical relationships between strengths and fluxes of photospheric magnetic fields, we show that the strong fields (spots, plages, and network) and the weak inter-network fields leave distinguishing features in their contributions to the RV variability. We also find that the fill factors and average unsigned magnetic fluxes of different features correlate differently with the RVs and hence warrant care in employing either of them as a proxy for RV variations. In addition, we examine disk-averaged UV intensities at 1600 and 1700 Å wavelength bands imaged by SDO/AIA and their performances as proxies for variations in different magnetic features. We find that the UV intensities provide a better measure of contributions of plage fields to RVs than the Ca II H-K emission indices, especially during high activity levels when the latter tend to saturate.

Speaker: Anisha Sen (Indian Institute of Astrophysics)

61 In Situ Observation of Mass Ejections Caused by Magnetic Reconnections in the Ionosphere of Mars

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 field regions with open magnetic fields. A plasma density cavity with signatures of magnetic reconnection that is directly evident for an eruptive mass ejection caught in the act indicates that a considerable amount of ionospheric mass has been rapidly ejected into space. Although Martian mass loss associated with magnetic reconnection has been reported previously, our results demonstrate that explosive mass ejections can occur even on partially magnetized planets without global magnetic fields. In this scenario, we suggest that strong localized magnetic fields extending above the exobase are needed. In situ observations reveal explosive mass ejections due to magnetic reconnection in the ionosphere of Mars, with a density cavity as direct evidence. Reconnection between strong open crustal fields can rapidly eject a large amount of mass from Mars.

Speaker: Yudong Ye (Sun Yat Sen University, Zhuhai, China)

20250123_MR_ION_MARS_ydye.pdf

62 The Sun as a Prototype of Stellar Variability

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 highly active cool stars, by magnetic features. Only stars showing large amplitude brightness fluctuations were detected as variable. Moderately active Sun-like stars were considered to be constant as their variability was hidden in the noise of most stellar observations. Only thanks to the advent of space missions doing highly sensitive photometry (mainly aimed at detecting exoplanets via planetary transits) have other sun-like stars been found to be variable in ways similar to the Sun. Whereas the causes of solar variability have been identified and are reasonably well understood, for stars, we are still at the start of the journey leading to a good understanding. Here the Sun serves as a prototype and guide, helping to interpret and understand the observed variability of cool stars. Stellar observations in turn also give new insights into the possible behavior of the Sun, particularly on timescales that are longer than those for which we have good solar data.

Speaker: Sami Solanki (Max Planck Institute for Solar System Research)

10:35 AM Coffee Break

Asteroseismology

63 Solar-like Stars: Seismology and Stellar Magnetic Activity

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 solar-like stars observed by space missions such as CoRoT and Kepler. By combining these observables with the internal structure from asteroseismic models, we can obtain a broader picture of how magnetic activity operates in stars. Thanks to the larger sample stars observed by space missions, we can study how magnetic activity evolves with different stellar parameters and with time. This also means that p-mode amplitudes are suppressed for very active stars preventing us from detecting them. For those more active stars, surface magnetism can be measured with photometric data, increasing the sample to several tens of thousands of stars. With this enlarged sample we can study the evolution of magnetic activity with age and Rossby number.

Speaker: Savita Mathur (Instituto de Astrofísica de Canarias)

64 Latitudinal Differential Rotation in Red Giants

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 asteroseismology in studying the differential rotation in stars. The envelope of a star doesn’t rotate with a constant rate along the latitude. For eg., the differential rotation between the equator and poles of the Sun is 30% of the average rotation rate. Measurements of differential rotation in stars could provide insights into the mechanisms of angular momentum transport and magnetic activity in stars. Theoretical simulations have predicted the possibility of anti-solar rotation (i.e. the poles rotating faster than the equator) in stars with slower rotation rates. However, so far, there have been only a couple of reliable observations of anti-solar rotation. I will present our results of detecting significant differential rotation in several red giants, with nearly half of them showing anti-solar rotation, and the others showing solar-like rotation. We use a machine learning algorithm to infer the key seismic parameters of a star, and then we use these inferences to set the prior probability distributions for MCMC (Markov chain Monte Carlo), a standard method for fitting the oscillation spectra of stars.

Speaker: Meenakshi Gaira (Tata Institute of Fundamental Research)

65 Anomalous Rotators and New Evolutionary Pathways in Red Giants

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 models applied to Kepler observations have revealed new physical insights into angular momentum transport, magnetism and structure evolution in the red-giant phase.

Speaker: Shravan Hanasoge (Tata Institute of Fundamental Research)

12:05 PM Lunch

Solar/Stellar Dynamo and Activity

66 Progress in Modelling Solar and Stellar Activity Cycles

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 advancements addressing this challenge, drawing connections with mean-field dynamo theory and Direct Numerical Simulations (DNS). Additionally, I will explore the implications of these findings for the modelling of solar and stellar cycles.

Speaker: Alfio Maurizio Bonanno (INAF Osservatorio Astrofisico di Catania)

67 Dynamo Modelling for Cycle Variability and Occurrence of Grand Minima in Sun-Like Stars at Different Rotation Rates

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 first time, model these observational trends using flux transport dynamo models. We build kinematic dynamo models of one solar mass star with different rotation rates. Differential rotation and meridional circulation are specified by computing them using equivalent mean-field hydrodynamic models of these stars. We include stochastic fluctuations in the Babcock-Leighton source of the poloidal field to capture the inherent fluctuations in the stellar convection. Based on extensive simulations, we find that rapidly rotating stars produce highly irregular cycles with strong magnetic fields and rarely produce Maunder-like grand minima, whereas the slowly-rotating stars (with a rotation period of 10 days and longer) produce smooth cycles of weaker strength, long-term modulation in the amplitude, and occasional extended grand minima. The average duration and the frequency of grand minima increase with decreasing rotation rate. These results can be understood as the tendency of less supercritical dynamo in slower rotating stars to be more prone to produce extended grand minima. We further conclude that even in rapidly rotating stars for which the star spots appear at high latitudes, the Babcock-Leighton dynamo operates.

Speaker: Bidya Binay Karak (IIT (BHU) Varanasi)

68 3D Radiative MHD Models of Cool Main-Sequence Starspots

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 model a K2V and an M0V starspot, along with a reference G2V starspot. The models show considerable complexity in thermodynamic structure, velocities and field distribution. Various properties like contrast between spot and quiet star region, as well as horizontal velocities at the surface, scale with stellar type. These models represent a first step towards modelling this aspect of stellar variability more accurately.

Speaker: Tanayveer Singh Bhatia (Max Planck Institute for Solar System Research)

IIAP2025.odp

IIAP2025.pdf

69 Star-Planet Interactions: From Solar System Planets to Exoplanets

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 implications for protection of space-based technologies and (exo)planetary habitability. In this talk, I shall discuss the fascinating science underlying star-planet interactions – focussing on our research on the interplay of magnetized stellar winds and (exo)planets with and without magnetospheres.

Speaker: Dibyendu Nandi (IISER Kolkata)

2:45 PM Coffee Break

Stellar Activity as a Limiting Factor for Characterising Exoplanets

70 Stellar Activity as a Limiting Factor for the Discovery and Characterisation of Exoplanets

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 stellar hosts can overwhelm the instrument error and become the dominant source of uncertainty. An ambitious, comprehensive effort to model and correct for stellar activity effects must therefore be undertaken if we wish to explore the realm of exo-Earths. In this talk, I will review the current understanding of the impact of stellar activity on planet detection and characterisation, as well as some of the most promising efforts to decontaminate RV and transmission spectroscopy data. I will specifically discuss our approach, which is based on the unique combination of a physical model and contemporaneous multi-technique monitoring. The SPOTLESS project will implement this methodology by building a realistic stellar activity simulator and developing correction strategies using, for example, machine learning algorithms and direct inversion. With ongoing efforts, we should be able to attain new, challenging exoplanet RV discoveries and unbiased transmission spectra.

Speaker: Ignasi Ribas (Institut d'Estudis Espacials de Catalunya (IEEC) & Institut de Ciències de l'Espai (ICE, CSIC))

71 Magnetospheric Dynamics and Atmospheric Mass Loss Driven by Solar-Stellar Winds and Storms

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 magnetotail current density during reconnection events in (exo)planetary magnetospheres. We find a highly correlated polarity reversal of the induced magnetosphere with stellar wind magnetic field orientations for unmagnetised planets, and as the planetary magnetospheric field strength increases, the polarity reversal in the vicinity of the planet becomes less pronounced. Detailed analysis of the magnetotail current density during polarity reversals for unmagnetized planets aligns closely with observations of the Venusian-induced magnetosphere. We discuss the implications of our findings for solar forcing of planetary atmospheres that are relevant for upcoming space missions.

Speaker: Sakshi Gupta (Indian Institute of Science Education and Research Kolkata)

72 Magnetic Interaction of Stellar Coronal Mass Ejections with Close-In Exoplanets

Coronal Mass Ejections (CMEs) erupting from the host star are expected to have enormous effects on the atmospheric erosion processes of the orbiting planets. For planets with a magnetosphere, the embedded magnetic field in the CMEs is thought to be the most important parameter to affect planetary mass loss. In this work, we investigate the effect of different magnetic field structures of stellar CMEs on the atmosphere of a hot Jupiter with a dipolar magnetosphere. We use a time-dependent 3D radiative magnetohydrodynamics (MHD) atmospheric escape model that self-consistently models the outflow from hot Jupiters magnetosphere and its interaction with stellar CMEs. For our study, we consider three configurations of magnetic field embedded in stellar CMEs – (a) northward Bz component, (b) southward Bz component, and (c) radial component. We find that both the CMEs with northward Bz component and southward Bz component increase the mass-loss rate when CME enters the stellar side but the mass-loss rate becomes higher for the CME with northward Bz component when it arrives at the opposite side. The largest magnetopause is found for the CME with a southward Bz component when the dipole and the CME magnetic fields have the same direction. We also find that during the passage of a CME, the planetary magnetosphere goes through three distinct changes - (1) compressed magnetosphere, (2) enlarged magnetosphere, and (3) relaxed magnetosphere for all three considered CME configurations. We compute synthetic Ly-𝛼 transits at different times during the passage of the CMEs. The synthetic Ly-𝛼 transit absorption generally increases when the CME is in interaction with the planet for all three magnetic configurations. The maximum Ly-𝛼 absorption is found for the radial CME case when the magnetosphere is the most compressed.

Speaker: Gopal Hazra (IIT Kanpur)

Friday, January 24

Solar Active Regions and Eruptions

73 Eruptive and Non-Eruptive Solar Active Regions: What Sets them Apart?

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 significant topological feature of eruptivity, namely, the magnetic polarity inversion line (PIL) and adjacent subregions in active regions, along with their size and intensity characterizations. How all these diagnostics, inferred as low in the solar atmosphere as vector magnetic field measurements exist, transpire to the overlying coronal volume will also be discussed. This is an action often overlooked, despite being necessary to enforce consistency between different physical layers, from where active-region observations and physically meaningful moments are available to where eruptions actually occur. A key question is how one might tell of imminent flaring activity or eruptivity in active regions, at physically meaningful timescales of hours or days before these instability manifestations. This question has physical and operational aspects, the latter in terms of space weather forecasting efforts, but we will be focusing on physics. Space missions along and beyond the Sun-Earth line, such as SOHO, SDO, STEREO and, to an increasing extent, Solar Orbiter and Parker Solar Probe, have also made important or even decisive contributions to our present understanding of solar active regions. We will sample key observations from these missions that have shaped this understanding and have enabled us to pursue further progress.

Speaker: Manolis Georgoulis (Johns Hopkins Applied Physics Laboratory)

74 Coronal Structure and Rotation Enforced by Nested Active Region Emergence: Near-Continuous Monitoring of an Active Nest with Solar Orbiter

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 contribute significantly to solar activity and modify the structure of the Sun’s coronal magnetic field. As a large fraction, up to 50%, of active regions form in this way, a better understanding of their formation and evolution is needed to improve space weather forecasts as well as model the magnetic connectivity of spacecraft in the heliosphere. The strong magnetic fields that develop in active nests couple the surface rotation rate to the coronal plasma, leading to enhanced rotational flows in the solar wind. ESA’s Solar Orbiter now acts as a far-side monitor of solar activity for several months each year. This facilitates near-continuous observations of long-lived active regions that span multiple solar rotations. We use these observations to build a complete record of activity for an active nest identified in 2022 (during the rising phase of activity for cycle 25). We constrain the influence this active nest had on the coronal magnetic field and solar wind outflow using measurements from NASA’s Parker Solar Probe in the inner heliosphere.

Speaker: Adam Finley (CEA Paris-Saclay)

75 Global Coronal Magnetic Field Modelling to Study Solar Eruptive Events

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 evolution over many months demonstrate that the non-potential evolution of the corona leads to the accumulation of magnetic free energy and helicity, which is periodically shed in eruptive events. We find that these events fall into two distinct classes: One set of events is caused by eruption and ejection of low-lying coronal flux ropes, and they could explain the origin of filament-erupting CMEs. The other set of events is not driven by the destabilisation of low-lying structures but rather by the eruption of overlying sheared arcades. These are associated with streamer blowouts or stealth CMEs, which are sources of problematic geomagnetic storms. Further investigation into the second class of events predicts the occurrence of repeated eruptions without clear low-coronal signatures from such arcades, provided that the high, overlying magnetic field lines are sufficiently sheared by differential rotation. Thus, our study suggests that magnetofrictional models can, in principle, provide early indication - pre-onset of CMEs, irrespective of whether they originate from the eruption of a low-coronal flux rope.

Speaker: Prantika Bhowmik (Department of Physics, Indian Institute of Science Bangalore)

76 What Could Bridge the Gap Between Medium and Shorter-Term Solar Flare Prediction Methods?

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 predictions provide a broad understanding of solar activity, facilitating better preparedness for heightened periods of solar activity. In contrast, short-term predictions are based on recent solar observations and the rapidly evolving phenomena on the solar surface, offering warnings within hours or a daily timeframe. By merging medium-term and short-term insights, a more robust and effective solar flare prediction framework can be established. This comprehensive approach enhances the accuracy of specific flare event predictions and significantly advances our grasp of solar dynamics.

Speaker: Marianna Korsos (University of Sheffield)

77 Reconstruction of Interplanetary Magnetic Field: A Novel Approach to Constrain the Solar Source Surface and Its Response to Solar Activity

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 integrating a data-driven photospheric flux transport model, coronal magnetic field extrapolations, and historical geomagnetic data. We introduce a novel technique for optimizing polar flux to match observations to address the persistent challenge of solar open flux, which is critical for accurate IMF reconstruction. We also explore long-term variations in solar open flux across different phases of solar activity, offering improved physical constraints on the solar source surface height and its response to solar activity levels. This work enhances our ability to reconstruct and predict solar open flux and solar wind dynamics.

Speaker: Shaonwita Pal (IISER Kolkata)

78 Multiwavelength Study of Pre-flare Signatures Using Aditya-L1

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 originating from different layers of the solar atmosphere. In this study, we use simultaneous observations from Solar Ultraviolet Imaging Telescope (SUIT), High Energy L1 Orbiting X-ray Spectrometer (HEL1OS) and SOlar Low Energy Spectrometer (SoLEXS) that observe the sun in the near ultraviolet (NUV) Soft X-ray and Hard X-ray to study the signatures during multiple pre-flare conditions. We also use HMI onboard SDO to study the magnetic parameters. Preliminary results suggest enhancements in NUV, especially in calcium and magnesium emissions, which are connected with the flux emergence during preflare conditions.

Speaker: Adithya HN (Manipal Centre for Natural Sciences, Manipal Academy for Higher Education, Manipal, Karnataka, India)

Poster Session-II / Coffee Break

Extreme Events

79 Connecting Sun to Heliosphere over Time and Space: Extreme Events

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 magnetic content/complexity. Ultimately, the energy that powers CMEs and flares are stored in active regions, so regions of extraordinary size and magnetic field strength have the potential to produce extreme events. The mass and magnetic field of CMEs and solar flare photons propagate into the heliosphere that can cause widespread impact on planets and human-made technological systems. Obvious examples of extreme consequences are super-intense geomagnetic storms caused by CME impact on Earth’s magnetosphere and high energy/intensity solar energetic particle (SEP) events caused by CME-driven shocks in the corona and interplanetary medium. Geomagnetic storms and SEP events result in a number of effects in various layers of planetary environment, especially in geospacer. Cumulative distribution of all available observations of event sizes can be used to identify the tail of the distribution and estimate the extremeness on various timescales (e.g., one-in-100-year events). I discuss cumulative distribution of CME kinetic energy, flare size, SEP fluence, and strength of geomagnetic storms and how historical space weather events fall on the tail of these distributions. If the mechanism that produces an extreme event is no different from the regular events, the extreme event if often referred to as a “black swan” event. On the other hand, if an extreme event deviates significantly from the tail, a different mechanism may be coming into play, making it a “dragon king” event. This talk summarizes some of these aspects of extreme events in the Sun-Earth system.

Speaker: Nat Gopalswamy (NASA Goddard Space Flight Center)

80 A Study Of The May 10-11 Superstorm : Solar Sources And Technological Impacts

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, the energy transferred from the solar wind also causes increased Joule heating, which leads to the thermosphere expanding upward. This expansion raises the thermospheric density at satellite altitudes, increasing drag and affecting their orbital lifetimes. Extreme geomagnetic storms can also severely disrupt GPS-dependent technology by altering radio signal paths through the atmosphere. The geomagnetic storm of May 10-11, 2024, produced vivid auroras seen as far south as 34° N in Ladakh and 18° N in Puerto Rico, highlighting the storm's intensity. Multiple reports of GPS-reliant farm equipment failures in the U.S. and satellite de-orbiting from various regions surfaced as the storm intensified. In fact, geomagnetic indices indicate that this storm was the most powerful in the past 20 years. In our study, we investigate the solar sources of the geomagnetic storm and identify their near Earth counterparts from an extremely complex in-situ solar wind profile at L1. We apply magnetohydrodynamic and empirical simulations to assess the impact of the CMEs on Earth's magnetosphere and satellite orbital lifetimes. Additionally, our work examines this storm in a historical context to compare its strength to previous extreme storms and likelihood of occurrence.

Speaker: Yoshita Baruah (Center of Excellence in Space Sciences India, Indian Institute of Science Education and Research Kolkata)

81 Constraining CME Magnetic Flux in EUHFORIA Using Helicity Content: Case Study of the 10 March 2022 CME Observed by Solar Orbiter

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 magnetic helicity content of the CME to determine its axial field strength (B0), which we equate to the magnetic field strength (Bspheromak) at the spheromak's magnetic axis. The amount of helicity transported to the CME has been estimated by taking the net helicity difference between the pre- and post-eruptive phase of the source active region (AR). This estimated helicity budget of the associated CME is further used to constrain a Lundquist flux-rope model with geometrical parameters obtained through a graduated cylindrical shell (GCS) model to determine B0 at the GCS-fitted height. From this, Bspheromak and radius derived from the geometrical parameters of the CME, we estimate the CME’s toroidal magnetic flux, which is then used as input for the EUHFORIA simulation. We validate our approach by applying the method to the CME that erupted on 10 March 2022 from NOAA AR 12962, observed by Solar Orbiter at 7.8 degrees east of the Sun-Earth line at a distance of 0.43 AU, complemented by WIND measurements at L1 (0.99 AU). The CME’s helicity was estimated to be $(-7.1 ± 1.2) x 10^{41} Mx^2$. The CME’s axial magnetic field at GCS fitted height of 7.6 Rs was B0=2067 ± 405 nT, with a power-law variation with distance extending to L1 and characterised by an index of −1.23 ± 0.18. Extrapolating this magnetic field to the inner boundary of EUHFORIA (21.5 Rs), we obtained Bspheromak=1058 ± 288 nT, from which we estimate the spheromak’s toroidal flux as (10.32 ± 6.4) × 10¹² Wb. By modelling this CME from 21.5 Rs to Earth, we assess how well in situ magnetic field measurements align with the model’s predictions at 0.43 AU and 0.99 AU. We report a reasonable agreement which demonstrates our method’s efficiency and value.

Speaker: Shifana Koya (University of Ioaninna Greece)

82 Interplanetary Shocks at 1 AU: Automated Detection and Characterization Over Solar Cycles (1996–2023)

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 speed, Mach number, shock normal direction, and compression ratio were calculated, with their annual variations examined across two solar cycles. The origins of these shocks are also investigated, differentiating between those driven by coronal mass ejections (CMEs) and corotating interaction regions (CIRs). Additionally, we explored the impact of these shocks on Earth by correlating them with storm sudden commencement (SSC) events. This work offers new insights into shock physics, space weather, and their broader implications.

Speaker: Wageesh Mishra (IIA, Bengaluru)

12:30 PM Lunch

Representative Results from New Heliospheric Missions

83 Recent Results on Solar Wind and Suprathermal Ions in the Interplanetary Medium and the Relevance of Aditya Solar Wind Particle Experiment (ASPEX) On-Board Aditya-L1

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 interaction region (SIR). On some occasions, AHe goes to very low values (compared to what is expected in the solar wind in general) as well. Some of the insights obtained from the recent results will be presented related to the above themes. Also, changes in the suprathermal ions in the quiet interplanetary medium during the last two solar cycles will be presented and contrasted with the corresponding variations in the stream interaction regions. Recent results obtained by analysing the upstream (of the terrestrial bow shock) events will also be discussed. It will be argued that directional, alpha-proton separated measurements of the ions in the interplanetary medium in both low and high energies by the Aditya Solar wind Particle Experiment on-board Aditya-L1 holds great potential to address some of the unresolved problems related to solar and heliospheric processes.

Speaker: Dibyendu Chakrabarty (Physical Research Laboratory)

84 Multi-Spacecraft Exploration of the Formation Stages of a Coronal Mass Ejection During a Composite Flare: Heating, Particle Acceleration, and Hot-Channel Eruption

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 large-scale reconnection in triggering the activation and eruption of an MFR. The eruption occurred in solar active region NOAA 12975 and observed from a suite of instruments including two solar X-ray telescopes: Solar X-ray Monitor (XSM) on board Chandrayaan-2 (Ch-2) and the Spectrometer Telescope for Imaging X-rays (STIX) on board Solar Orbiter (SO). During our observing period, the SO-Sun-Earth angle was 85.2 degree, making it possible to address the relationship between emission from different segments of the flare loops, viz. coronal loop-tops and foot-points sources. A comparison between the imaging observations from Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO) in extreme ultraviolet (EUV) channels and X-ray time profiles at multiple energy bands clearly reveal the physical connection between the two events as the rising EUV hot channel (i.e. MFR in low corona) attains eruptive motions around the transition period between the two flaring episodes. Our observations indicate that the MFR initially ascended with a projected speed of ≈80 km s-1 while the corresponding halo-CME expanded with a speed of ≈900 km s-1 within ≈3−11 RꙨ. The analysis of high-resolution X-ray spectra at 1-15 keV energies from XSM/Ch-2 reveal that the highest plasma temperature was attained at the peak C6.3 flare which did not show significant increase during the subsequent M1 event; on the other hand, the emission measure (EM) almost doubled during the peak of M-class event in comparison to that at the peak of the preceding event. The observations provide new insights on the role of precursor emission toward the destabilization of MFR. A distinct C6.3 event happening as a precursor to M1.0 flare clearly points toward a feedback relationship between large-scale, two-phase magnetic reconnection and corresponding step-wise evolution of the MFR.

Speaker: Bhuwan Joshi (Udaipur Solar Observatory, Physical Research Laboratory)

85 Investigating the Possible Origin of Magnetic Switchbacks in the Low Solar Atmosphere

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 they are ubiquitous in the young solar wind. There is currently no unique generation model explaining all the switchback’s observed properties. However, there is a growing consensus that dynamical processes, such as a variety of jetting activity in the solar atmosphere can be the seed of deflections becoming switchbacks in the expanding solar wind. I will present two recent works, one observational and one numerical, in which we aim to test this hypothesis. These two approaches are complementary as from the observations (in situ and remote-sensing ones) alone we are missing informations on the propagation of the structures. I will conclude on the current state of knowledge and on what one should focus on in future studies.

Speaker: Clara Froment (CNRS/LPC2E-Orléans)

86 The Coherent Morphology and Evolution of Solar Coronal Loops

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 better understand the dynamics of the magnetic field and the nature of plasma heating processes operating in the corona. The spatial morphology of coronal loops is still not fully understood. Some studies have indicated that coronal loops might be apparent optical illusions, similar to veils, caused by folds in the two-dimensional current sheets. Stereoscopic observations of coronal loops will be crucial to decipher their morphology. To this end, we used high-resolution imaging data from the Extreme Ultraviolet Imager (EUI) on the Solar Orbiter spacecraft and the Atmospheric Imaging Assembly on the Solar Dynamics Observatory to stereoscopically analyze a set of coronal loops in an active region. Our findings show that the loops have nearly circular cross-sectional widths and consistent intensity variations along their lengths over timescales of 30 minutes. We suggest that the morphology of coronal loops is consistent with three-dimensional flux tube-like structures and not emissions from randomly aligned two-dimensional current sheets along the line of sight as proposed in the 'coronal veil' hypothesis.

Speaker: Bhinva Ram (Max Planck Institute for Solar System Research)

87 Polarization Characteristics of Active Solar Radio Emissions: Studies with SKAO Precursors and Pathfinders

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 use of imaging techniques for solar and coronal studies at low radio frequencies. Most existing research is based on analyzing dynamic spectra, which do not provide imaging information. This is now set to change due to two primary reasons. The first is the availability of the next-generation telescopes, such as the Murchison Widefield Array (MWA), LOw Frequency ARray (LOFAR), and the upgraded Giant Metrewave Radio Telescope (uGMRT), all precursors or pathfinders for the Square Kilometre Observatory (SKAO) expected to become available by the end of this decade. The second is the advances in calibration and imaging algorithms, which have enabled the generation of high fidelity, full polarimetric spectroscopic snapshot images of the Sun from the data obtained using these instruments. These images facilitate the study of active emissions varying on small spectral and temporal scales. We have conducted full polarization imaging studies of multiple active solar radio emissions using MWA, LOFAR, and uGMRT. Our findings reveal that these emissions are predominantly circularly polarized, with polarization fractions exhibiting significant variation, and almost always remaining significantly lower than theoretical expectations. Notably, the location of the polarized sources appears to be shifted by several arcseconds to few arcminutes relative to total intensity sources with the polarized source being more compact, hinting that a substantial amount of polarization might have been lost due to scattering.
We will summarize our results and discuss their potential implications.

Speaker: Soham Dey (National Centre for Radio Astrophysics)

Poster Session-II / Coffee Break

Radio Input to Heliospheric Studies and Space Weather

88 Solar and Heliospheric Science from the New Generation Radio Telescopes: Status and Opportunities

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 and pathfinders of the Square Kilometre Array Observatory (SKAO) and the SKAO itself (expected first-light 2029). The vastly improved observational abilities of these instruments are very well aligned with the needs of heliophysics. Between the various instruments and available techniques, they can be used to study regions from the base of the corona to beyond an AU and address a large variety of science targets. Considerable work has already been devoted towards enabling heliophysics with these instruments, which are optimized to look at faint radio sources orders of magnitude weaker than the Sun. This talk will showcase some example science areas where considerable progress has been made, share the status and near-term plans for radio heliophysics observations with the new-generation instruments and the science opportunities they present.

Speaker: Divya Oberoi (National Centre for Radio Astrophysics, Tata Institute of Fundamental Research)

89 Bringing Together World’s Best Radio Telescopes for Remote Sensing of Heliospheric Magnetic Field

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 (LoS) integrated magnetic fields when a plasma blob intercepts that LoS. To date, this technique has been limited at coronal heights <15 R_sun using high-frequency telescopes with lower sensitivity to magnetic field strength and narrow fields of view (FoV), such as the JVLA. Over the past two decades, new-generation ground-based radio telescopes like MWA, LOFAR, ASKAP, and MeerKAT have become operational. These telescopes offer wide FoVs and lower observing frequencies, which can overcome previous limitations. Despite their capabilities, these instruments face challenges in calibration and trigger time-of-opportunity observations for space-weather events. This talk presents our recent efforts to address these challenges by utilizing these leading radio telescopes and preparing for upcoming new-generation radio telescopes (like ngVLA, SKAO) for heliospheric magnetic field measurements using radio polarimetry, a technique we call "Heliopolarimetry." By leveraging these advancements, along with other white-light missions (like PUNCH), we aim to enhance space-weather research and prediction capabilities.

Speaker: Devojyoti Kansabanik (University Corporation for Atmospheric Research)

90 Radio Eyes for the Sun, Heliosphere and Ionosphere: Status and Plans for the LOFAR2.0 Era.

The Low-Frequency Array (LOFAR) has established itself as a formidable instrument in the field of solar physics and space weather, providing a unique vantage point for observing the Sun, heliosphere, and ionosphere. As we transition into the LOFAR2.0 era, this abstract outlines the current status and future plans for leveraging LOFAR's capabilities, and the LOFAR IDOLS (Incremental Development of LOFAR Space-weather) project. LOFAR's current work in solar physics involves high-resolution imaging and dynamic spectral analysis, enabling detailed observations of solar radio bursts and other coronal heliosphere and ionosphere phenomena. These observations are critical for understanding the mechanisms behind solar activity and improving our predictive models of space weather events. The LOFAR IDOLS station, a dedicated space-weather science facility, has been instrumental in advancing this work. It currently provides continuous monitoring of the ionosphere and Sun, tracking disturbances that can affect space wetaher on Earth, but also the astronomical observations of LOFAR itself. The LOFAR2.0 upgrade promises to enhance these capabilities significantly. Plans include improving the sensitivity and spatial resolution of the array, and the simoultaneus observations in LBA and HBA, which will allow for even more precise and broad imaging and tracking of solar phenomena. This will enable researchers to dissect the fine structures within the solar corona and track the development of space weather events with greater accuracy. Furthermore, the LOFAR IDOLS project is set to continue observation during the period of transition to LOFAR2.0 enabling us to test the monitorning capabilities. In conclusion, the LOFAR2.0 era opens a new opportunity for solar and space weather research. With the ongoing work and future plans for the LOFAR IDOLS station and LOFAR2.0 observations, we are preparing to gain deeper insights into the Sun's influence on our space environment and to develop more robust forecasting capabilities for space weather phenomena.

Speaker: Pietro Zucca (ASTRON)

91 The First Detailed Polarimetric Study of a Type-II Solar Radio Burst with the MWA

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 concern of space weather. The evolution and geo-effectiveness of these eruptions are governed by their entrained magnetic fields and interactions with the ambient magnetized plasma medium. Hence, understanding the entrained magnetic fields and the ambient medium is crucial. Polarimetric properties of metric type-IIs are promising diagnostics to understand the strength and topology of the CME-shock entrained magnetic fields and ambient plasma medium at the low-coronal heights where only a handful of direct probes are available. The majority of previous studies are based on dynamic spectra that do not provide spatially resolved information. Polarized emissions can be both positive and negative; hence, spatially integrated information may lead to incorrect measurements of polarization properties. For robust estimations of these spatio-temporally variable emissions, high-fidelity spectro-polarimetric images are essential. Instruments like the Murchison Widefield Array (MWA) and its dedicated robust solar calibration and imaging pipeline have made such studies possible. We have used this pipeline to carry out a detailed polarimetric study of a type-II solar radio burst observed with the MWA. Here we summarize the new findings from this work and discuss the potential of high-fidelity spectro-polarimetric imaging studies for understanding the shock-entrained magnetic fields and the plasma medium at the lower corona.

Speaker: Puja Majee (National Centre for Radio Astrophysics, Tata Institute of Fundamental Research)

92 Type II Radio Burst Without Coronal Mass Ejection

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 observed on November 2, 2023, characterised by split band features. Notably, no CME was detected with space-based coronagraphs during this event. However, a M1.6 class flare was observed just before the type II burst and an EUV disturbance was observed expanding into surrounding regions. Further analysis will be performed to determine the cause of the EUV disturbance as due to a failed eruption. This talk will discuss preliminary findings on the generation of the shock and shed light on the occurrence of type II bursts in the absence of white-light CMEs.

Speaker: Anshu Kumari (Physical Research Laboratory (PRL))

Closing Session - KSO Specific Screening/Release of Documents