Udaipur Solar Observatory | Physical Research Laboratory

2026

Spectroscopic and Imaging Diagnostics of Thermodynamic and Magnetic Conditions in Solar Active Regions

Date: 2026-02-06
Speaker: Mr. B. Suresh Babu
Venue: USO Seminar Hall

Abstract

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

2025

Introduction to Solar Radiophysics: Theory and Observations

Date: 2025-12-16
Speaker: Ms Divya Paliwal
Venue: USO Seminar Hall

Abstract

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

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

High resolution imaging with MAST

Date: 2025-12-15
Speaker: Shruti Sinha
Venue: USO Seminar Hall

Abstract

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

Probing Solar Polar Activity through EUV and Radio Observations

Date: 2025-11-18
Speaker: Rohan Bose
Venue: USO Seminar Hall

Abstract

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

Observational study of the atmospheric gravity waves in the lower solar atmosphere

Date: 2025-11-12
Speaker: Ravi Chaurasiya
Venue: USO Seminar Hall

Abstract

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

Navigation with Indian Constellation

Date: 2025-11-10
Speaker: Ms. Aakanksha Avnish Bhardwajan
Venue: USO Seminar Hall

Abstract

Navigation with Indian Constellation

Numerical exploration of a B-Class flare using the synergy between XSM, GOES, AIA, and HMI

Date: 2025-11-07
Speaker: Simrat Kaur
Venue: USO Seminar Hall

Abstract

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

Unraveling solar eruptions using high resolution ground-based and space-borne observations

Date: 2025-09-12
Speaker: Dr. Reetika Joshi
Venue: USO Seminar Hall

Abstract

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

Radio eyes for the Sun, Heliosphere and Ionosphere: Status and plans for the LOFAR2.0 era.

Date: 2025-01-17
Speaker: Dr. Pietro Zucca
Venue: USO Seminar Hall

Abstract

The Low-Frequency Array (LOFAR) has established itself as a formidable instrument in the field of solar physics and spaceweather, 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.

On the Propagation of Shock Waves in the Transition Region and the Corona

Date: 2025-01-10
Speaker: Mr. Ravi Chaurasiya
Venue: USO Seminar Hall

Abstract

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 Î»-time plots of chromospheric spectral lines, such as HÎ± and Ca II. In this study, we investigate the formation and propagation of these shock waves in the chromosphere, examining their possible 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 at least up to the transition region. In this talk, I will discuss the identification of these shock waves, their propagation characteristics, and their potential implications for coronal dynamics.

Electron Density Mapping: Insights from Radio and In-Situ Observations & EUHFORIA Modeling

Date: 2025-01-09
Speaker: Ms Ketaki Despande
Venue: USO Seminar Hall

Abstract

Mapping the coronal electron density remains a challenging task, as we still rely on rather old 1D electron density models, most of which are derived from remote sensing observations and lack validation with in situ measurements. The novel observations from Parker Solar Probe (PSP) provide a unique opportunity to validate these models and enhance space weather modeling capabilities. In this study, we analyze type III radio bursts observed during PSP’s second perihelion. By employing radio triangulation, we estimate the 3D radio source positions and map the electron densities along the burst propagation path. These results are then compared with in situ electron density measurements from PSP. Additionally, we use EUHFORIA (European Heliospheric Forecasting Information Asset) to model electron densities at the PSP location and the radio source positions. Our findings indicate that bursts occurring within a few minutes from the same source can exhibit significantly different propagation paths. A comparison between radio-derived and in situ densities reveals a discrepancy of one order of magnitude. We also perform simulations using GONG and ADAPT-GONG magnetic maps as input. Both simulations suggest that type III bursts propagate along higher-density regions; however, results obtained with ADAPT-GONG maps show a better match with PSP in situ densities and predict higher density values overall. These results highlight the importance of validating remote sensing electron density models with in situ observations and demonstrate the impact of different magnetic field inputs on space weather modeling. The improved agreement with ADAPT-GONG maps suggests that incorporating more dynamic and data-driven models can enhance the accuracy of electron density estimations, ultimately improving our understanding of solar wind structures and radio wave propagation in the heliosphere.

2024

Observational determination of magnetic helicity and energy flux in the solar active regions.

Date: 2024-12-27
Speaker: Mr. Dinesh Mishra
Venue: USO Seminar Hall

Abstract

Magnetic helicity measures the degree of twisting of magnetic flux tubes, the shearing of magnetic arcades, and the interlinking of magnetic flux tubes. It plays an essential role in understanding the evolution of magnetic fields in the solar active regions and the triggering mechanism of solar transients that take place in the solar atmosphere, viz., flares and CMEs. In this talk, I will discuss about the estimation of magnetic helicity and the associated energy flux in the solar active regions using the observed photospheric vector magnetic fields and their importance.

Introduction to Solar Flares and Magnetic Reconnection.

Date: 2024-12-26
Speaker: Ms. Simrat Kaur
Venue: USO Seminar Hall

Abstract

Solar flares are sudden explosive events on the Sun that release energy through heating, electromagnetic radiation, and the acceleration of charged particles. These events are believed to be the manifestations of the magnetic reconnection process and can release energy ranging from 10^23 erg to 10^32 erg. In this seminar, I will discuss Solar flares and how they are connected to magnetic reconnection.

Solar Flares: Multi-wavelength Observations

Date: 2024-12-24
Speaker: Mr. Vishwa Vijay Singh
Venue: USO Seminar Hall

Abstract

Solar flares are among the most energetic events in the solar system, characterized by the sudden release of magnetic energy stored in the Sun’s corona. These phenomena emit radiation across the entire electromagnetic spectrum, from radio to γ-rays. Multi-wavelength observations provide a comprehensive understanding of the physical processes driving solar flares, including energy release, particle acceleration, plasma heating, and large-scale coronal restructuring. In this seminar, I will highlight the complementary nature of multi-wavelength observations in understanding the temporal and spatial evolution of solar flares. Additionally, we will discuss the role of magnetic reconnection and its association with large-scale phenomena such as coronal mass ejections (CMEs).

Properties of Sunspot Umbral Dots

Date: 2024-12-20
Speaker: Mr. Amit Chaturvedi
Venue: USO Seminar Hall

Abstract

Umbral Dots (UDs) are small, bright structures seen in the dark umbral core of pores and sunspots. They represent convective intrusions in the highly magnetized surroundings of the sunspot's umbra. In this talk, I will review the photometric, kinematic, and magnetic properties of UDs from high resolution ground- and space-based observations.

Exploring small-scale transient brightenings in the context of solar atmospheric heating

Date: 2024-12-19
Speaker: Mr. Hasil Dixit
Venue: USO Seminar Hall

Abstract

Improving Solar Wind Forecasting Model Over the Phase of Solar Cycle - Source Surface Height Optimization and Magnetogram Impact

Date: 2024-12-16
Speaker: Mr. Sandeep Kumar
Venue: USO Seminar Hall

Abstract

The operational solar wind velocity prediction models used by the community are based on the Potential Field Source Surface (PFSS) model of the magnetic field. The output of PFSS serves as input in the heliospheric models to provide solar wind velocity predictions at L1. Previous studies in the context of the prediction of open magnetic flux observed at L1 have suggested different source surface heights ($R_{ss}$) in the PFSS model at different phases of the solar cycle (SC). We investigate the effects and necessity of optimizing the $R_{ss}$ in the PFSS model in the context of its use in the popular Wang Sheeley and Arge (WSA) model for solar wind velocity prediction. We used Heliospheric Upwind Extrapolation (HUX) to extrapolate solar wind velocity in the heliosphere. We performed a study of 16 Carrington Rotations (CR) at different phases of the SC24 and SC25, using different types of magnetograms and WSA model parameters. We combine the coronal models (PFSS+WSA) with the heliospheric model (HUX) to predict solar wind velocity at L1 in our framework, i.e., PFSS+WSA+HUX. Our study suggests using a higher $R_{ss}$ ($3.0$ $R_\odot$) compared to the conventional $R_{ss}$ (2.5 $R_\odot$) near the solar minimum, resulting in an increase in the average performance of the framework. We found that the improved performance of the framework by 2 times with zero-point corrected maps, as compared to the standard full Carrington maps, can be attributed to its capability to capture the global magnetic field. This was also confirmed by comparing the extrapolated global magnetic field structures with the large-scale corona observed in the extended field of view of the PROBA2/SWAP images.

An X-ray Perspective on Multi-scale Solar Flares: Spectroscopy to Polarimetry

Date: 2024-12-06
Speaker: Dr. Mithun Neelakandan P S
Venue: USO Seminar Hall

Abstract

Solar flares have a wide range of intensity scales ranging from large X-class flares to microflares to hypothesized nanoflares that may be responsible for coronal heating. Investigations of multi-scale solar flares, from large flares to the smallest microflares, are key to the missing pieces in our understanding of the flaring process and coronal heating. As the flaring plasma and accelerated electrons emit profusely in soft and hard X-rays, X-ray spectroscopic observations offer the most direct diagnostics of the thermal and non-thermal particle populations in flares and, thus, insights into the energy release mechanisms in flares. Solar X-ray Monitor (XSM) onboard the Chandrayaan-2 mission provides disk-integrated X-ray spectral measurements of the Sun in the energy range of 1-15 keV, with a high dynamic range to observe sub-A class micro flares to large X-class flares. XSM has recently completed five years of continuous solar observations and in this talk I will highlight some of the major results using XSM observations on various aspects of multi-scale solar flares. I will also introduce other recently operational solar soft X-ray spectrometers on other missions and on the advantages of simultaneous analysis of soft X-ray spectra with the hard X-ray spectra from instruments such as Solar Orbiter STIX and Aditya L-1 HEL1OS. Going beyond spectroscopy, I will also discuss the potential of X-ray polarimetric observations of solar flares and our efforts towards a small satellite experiment, which would also be a pathfinder to an X-ray astronomy mission.

Studying solar flares with the X-ray telescope STIX on Solar Orbiter

Date: 2024-12-05
Speaker: Dr. Alexander Warmuth
Venue: USO Seminar Hall

Abstract

Of the six remote-sensing instruments aboard ESA's Solar Orbiter spacecraft, the Spectrometer/Telescope for Imaging X-rays (STIX) is the one dedicated to the study of solar flares. It performs X-ray imaging spectroscopy in the hard X-ray regime, which provides key physical diagnostics on both the hot thermal plasma as well as on the accelerated energetic electrons. During its operation since launch in 2020, STIX has detected over 56,000 solar flares. I will discuss how the STIX data are used to study energy release and particle acceleration in solar flares. In particular, I will focus on studies that use STIX jointly with other observational assets, such as the other remote-sensing instruments on Solar Orbiter, various instruments on other spacecraft, and in-situ particle detectors.

Fast Radio Bursts, a recent discovery in the field of Transients

Date: 2024-11-29
Speaker: Shruti Bhatporia
Venue: USO Seminar Hall

Abstract

Fast radio bursts (FRBs) are high-energy transient signals of millisecond duration detected by radio telescopes around the world. The origins of such FRBs are unknown. Therefore multiple theoretical models have been put forward to explain the phenomena. The frequency distribution of energy, duration, and waiting time for solar radio bursts is similar to that of FRBs. There is a correlation between the X-ray and radio luminosity of solar radio bursts, which suggests that the energetic electrons that cause radio emissions and X-ray flares have a common origin. In this talk, I will give an introduction to fast radio bursts and elaborate on ongoing multi-wavelength observation efforts.

PROBA-3 mission

Date: 2024-11-25
Speaker: Dr. Marek Jerzy Stęślicki
Venue: USO Seminar Hall

Abstract

Understanding Solar Eruptions: Ongoing and Future Research Programs at Space Research Centre of Polish Academy of Sciences.

Date: 2024-11-25
Speaker: Dr. Tomasz Maciej Mrozek
Venue: USO Seminar Hall

Abstract

Solar Physics Division, Space Research Centre of the Polish Academy of Sciences aims to observe and interpret solar X-rays. The group performed the first Polish space experiment (54 years ago) resulting in X-ray images obtained using several filters. SPD's increasing heritage led us to participate in the STIX experiment onboard the Solar Orbiter mission. The STIX's data analysis and interpretation is now our main activity. Apart from this, we are involved in CubiXSS experiment (NASA-lead) and MIRORES (all-Polish). During my seminar, I will shortly present the team, our experience, achievements and future ideas that we hope to realize.

Probing the Physics of Radiation and Particles Emitted During Energetically-Rich Solar Flares

Date: 2024-11-21
Speaker: Dr. Arun Kumar Awasthi
Venue: USO Seminar Hall

Abstract

Solar flares are one of the earliest observational signatures of solar eruptions. Although the X-class flares are the largest in intensity class, weaker (micro/nano) flares are more frequently occurring. Therefore, they are not only a suitable candidate for coronal heating, but their investigation may also provide crucial insights into the origin of particle emission from the Sun. By reconciling multi-wavelength observations, the standard flare energy release scheme puts forth the physical mechanism responsible for the radiation and particle emission during flares. However, this scheme is often challenged by the observations, particularly during weak flares that remained less investigated in the past owing to observational limitations. Therefore, it is yet to be understood if the weak flares are just a scaled-down version of large flares in the sense of physical processes. In this context, I will provide an overview of the role of weak flares as unique tracers of pre-eruptive plasma and magnetic field environment from the insights gained from our research investigations. I will also provide an overview of our future plans associating the physics of solar flares with the initiation mechanism of the coronal mass ejections with an emphasis on combining the observations from the ADITYA-L1 and the Solar orbiter missions.

Formation of homologous blowout jets and their large-scale consequences

Date: 2024-11-14
Speaker: Dr. Binal Patel
Venue: USO Seminar Hall

Abstract

Coronal jets are identified as transient coronal-temperature ejections from near the solar surface into the corona. A particular type of coronal jet, known as a blowout jet, has gained significant attention in recognizing the physical mechanism governing the jet-coronal mass ejection (CME) relationship. In this talk, I will discuss the formation of four CMEs originating from homologous blowout jets. All of the blowout jets originated from NOAA Active Region (AR) 11515 on 2012 July 2, within a time interval of 14 hr. All of the CMEs were wide (angular widths between 95–150 deg), and propagated with speeds ranging between 300 and 500 km/s in LASCO coronagraph images. Observations at various EUV wavelengths in Solar Dynamics Observatory/Atmospheric Imaging Assembly images reveal that in all the cases, the source region of the jets lies at the boundary of the leading part of AR 11515 that hosts a small filament before each event. Coronal magnetic field modeling based on nonlinear force-free extrapolations indicates that in each case, the filament is contained inside of a magnetic flux rope that remains constrained by overlying compact loops. The southern footpoint of each filament is rooted in the negative polarity region where the eruption onsets occur. This negative polarity region undergoes continuous flux changes, including emergence and cancellation with opposite polarity in the vicinity of the flux rope, and the EUV images reveal brightening episodes near the filament’s southeastern footpoint before each eruption. Therefore, these flux changes are likely the cause of the subsequent eruptions. These four homologous eruptions originate near adjacent feet of two large-scale loop systems connecting from that positive polarity part of the AR to two remote negative polarity regions, and result in large-scale consequences in the solar corona.

Flare Response in the Photosphere and Chromosphere: A Multi-line Spectropolarimetric Study

Date: 2024-10-04
Speaker: Dr. Rahul Yadav
Venue: USO Seminar Hall

Abstract

Solar flares, driven by magnetic reconnection in the corona, rapidly release immense energy into the solar atmosphere. Observations have shown that a flare influences different layers of the solar atmosphere almost simultaneously. However, it is still unclear how a flare impacts the lower solar atmosphere. Multi-line spectropolarimetric observations, covering different layers, are necessary to present a comprehensive view of flares. In this talk, I will explore the lower atmospheric response to flares using multi-line spectropolarimetric observations. I will demonstrate how these observations, combined with state-of-the-art multi-line inversion code, can be used to construct a stratification of physical parameters such as temperature, magnetic field vector, line-of-sight velocity, and macroturbulent velocity within a flaring atmosphere. The resulting semi-empirical model will be directly compared with theoretical flare models. Additionally, I will present recent findings from the 4-meter Daniel K. Inouye Solar Telescope, focusing on the rotation of pores associated with flares on a significantly smaller scale.

Understanding the Space Weather Impact of Coronal Mass Ejections Utilising Observations and Modelling

Date: 2024-09-30
Speaker: Dr. Ranadeep Sarkar
Venue: USO Seminar Hall

Abstract

The most challenging problem in space weather research is to predict the intensity of geomagnetic storms at Earth. During these storms modern infrastructure in space and on ground can experience significant hazards, such as disruptions of communication and power lines, and malfunctions or even a failure of satellites in orbit. The storms occur when an Earth-directed interplanetary coronal mass ejection (ICME) and/or their frontal sheath carries a strong southward interplanetary magnetic field (IMF) Bz. Therefore, the prediction of Bz inside both the ICME and sheath regions, is the prime requirement to forecast the severity of geomagnetic storms. Since the magnetic field of solar eruptions cannot reliably be measured via remote means, and direct continuous measurements of the Earth impacting solar transients are routinely available only very close to our planet, modelling of CME magnetic properties is paramount. In this talk, I will present a space weather modelling framework using both analytical and global MHD approaches that could prove to be an operation space weather forecasting tool to predict the geo-effectiveness of CMEs. This talk will also showcase the utilisation of multi-wavelength remote-sensing observations as well as multi-spacecraft in-situ observations at different heliocentric distances to constrain the space weather forecasting models. I will further discuss how data from India's space-based solar observatory, Aditya L1, and ISRO’s upcoming mission to Venus will play a crucial role in enhancing our understanding on the initiation and space-weather effects of CMEs.

Understanding the Space Weather Impact of Coronal Mass Ejections Utilising Observations and Modelling

Date: 2024-09-30
Speaker: Dr. Ranadeep Sarkar, Postdoctoral Fellow, Space Physics Department, University of Helsinki
Venue: USO Seminar Hall

Abstract

The most challenging problem in space weather research is to predict the intensity of geomagnetic storms at Earth. During these storms modern infrastructure in space and on ground can experience significant hazards, such as disruptions of communication and power lines, and malfunctions or even a failure of satellites in orbit. The storms occur when an Earth-directed interplanetary coronal mass ejection (ICME) and/or their frontal sheath carries a strong southward interplanetary magnetic field (IMF) Bz. Therefore, the prediction of Bz inside both the ICME and sheath regions, is the prime requirement to forecast the severity of geomagnetic storms. Since the magnetic field of solar eruptions cannot reliably be measured via remote means, and direct continuous measurements of the Earth impacting solar transients are routinely available only very close to our planet, modelling of CME magnetic properties is paramount. In this talk, I will present a space weather modelling framework using both analytical and global MHD approaches that could prove to be an operation space weather forecasting tool to predict the geo-effectiveness of CMEs. This talk will also showcase the utilisation of multi-wavelength remote-sensing observations as well as multi-spacecraft in-situ observations at different heliocentric distances to constrain the space weather forecasting models. I will further discuss how data from India's space-based solar observatory, Aditya L1, and ISRO’s upcoming mission to enus will play a crucial role in enhancing our understanding on the initiation and space-weather effects of CMEs.

Exploring three-dimensional magnetic nulls in the solar atmosphere: Theory and Simulations

Date: 2024-06-26
Speaker: Yogesh Kumar Maurya
Venue: USO Seminar Hall

Abstract

A three-dimensional (3D) magnetic null is a location where the magnetic field is zero. These nulls are abundant and are known to be important magnetic topologies in the solar atmosphere, playing vital roles in phenomena such as magnetic reconnection, jets, and circular ribbon flares. However, the mechanisms behind the generation of 3D nulls in such a dynamic atmosphere are yet to be fully explored. Recent magnetohydrodynamics (MHD) simulations propose that magnetic reconnection is responsible for both generating and annihilating 3D nulls, starting from an idealized magnetic field with a single proper radial null. In this seminar, we will briefly discuss the summary of the above work, highlighting the importance, structure, and properties of 3D nulls. We will further delve into the applications of these understandings to a more realistic scenario, incorporating the field line complexities inherent to a complex active region with thousands of preexisting nulls, and discuss the results. Additionally, we will explore the theme with an initially chaotic magnetic field devoid of any 3D nulls and discuss the results.

Plasma Motion in Sunspots

Date: 2024-06-25
Speaker: Prof. Debi Prasad Choudhary
Venue: USO Seminar Hall

Abstract

In this talk, I shall present the results to determine three dimensional thermal, magnetic and flow structure of sunspots using spectropolarimetric diagnostic in multiple spectral lines. We have used the observations with the spectropolarimeters at the focal plane of the Dunn Solar Telescope and analysis tools such as inversion codes and magnetic field extrapolation techniques developed by our group. In a series of investigations, we determine the detailed properties of Inverse Evershed Flow. Our results show that these flows are aligned along magnetic field lines that connect the outer penumbra with the outer end of the moat cell in the form of arched loops. We find that there is a positive field strength difference and the negative temperature difference between the inner and outer end point connected by these magnetic arches. This pressure difference induces a flow towards the sunspot following the siphon flow principle, which is in quantitative agreement of the observed flow speeds and those predicted from the pressure balance equation. I shall also introduce the ongoing and future research goals of our group. We are developing an analysis package for spectropolarimetric observations for the following purpose. 1. Develop and apply LTE and NLTE inversion codes to extract stratifications of temperature, velocity and magnetic field structure using multiple chromospheric and photospheric lines. 2. Develop an analysis tool for observations of the Halpha line. 3. Develop an automatic technique for integrating the piecewise continuous results of the H, He I at 1083 nm, and other lines into the analysis for a physically consistent stratification. 4. Determine magnetic and thermal atmospheric properties of sunspots for a full characterization of the solar atmospheric structure and its temporal evolution.

Probing the Physics of Radiation and Particles Emitted During Energetically-Rich Solar Flares

Date: 2024-06-21
Speaker: Dr. Arun Kumar Awasthi
Venue: USO Seminar Hall

Abstract

Solar flares are one of the earliest observational signature of solar eruptions. Although the X-class flares are the largest in intensity class, weak (micro/nano) flares are more frequent, making them a suitable candidate for coronal heating. By reconciling multi-wavelength observations, the standard flare energy release scheme to put forth the physical mechanism responsible for the production of emission and charged particles during flares. However, this scheme is often challenged by the observations, particularly during weak flares. Essentially, it is yet to be understood if the weak flares are just a scaled down version of large flares in the sense of physical processes. In this context, I will provide an overview of the research investigation conducted by us revealing the role of weak flares as unique tracers of pre-eruptive plasma and magnetic field environment. I will also provide an overview of future plans associating the physics of solar flares with the initiation mechanism of the coronal mass ejections with an emphasis on combining the observations from the ADITYA-L1 and the Solar orbiter missions.

On the Response of Transition Region and Corona to Rapid Excursions in the Chromosphere

Date: 2024-06-04
Speaker: Mr. Ravi Chaurasiya
Venue: USO Seminar Hall

Abstract

Spicules are the thin, hair/grass-like structures that are prominently observed at the chromospheric solar limb. It is believed that fibrils and Rapid Blue and Red Excursions (RBEs and RREs; collectively referred to as REs) correspond to on-disk counterparts of type I spicules & type II spicules, respectively. Our investigation focuses on observing the response of these REs alongside similar spectral features in the chromosphere, transition Region (TR), and corona, utilizing space-time plots derived from co-ordinated observations from SST/Hα, IRIS, and SDO. Our analysis reveals upflowing REs, promptly reaching temperatures characteristic of the TR and corona, indicating a multi-thermal nature. Similarly, downflowing features exhibiting similar spectral signatures over the disk display plasma motion from the corona to chromospheric temperatures, demonstrating a multithermal nature. In addition to distinct upflows and downflows, we observe sequential upflow and downflow along the same path, depicting a distinctive parabolic trajectory in space-time plots of observations sampling TR and various coronal passbands. Similar to isolated upflows and downflows, these REs also exhibit a multi-thermal nature throughout their trajectory. Furthermore, our results reveal a more intricate motion of the REs in which both upflow and downflow coexist at the same spatial location. On a different note, our analysis, utilizing coordinated IRIS spectral observations, shows spatio-temporal redshifts/downflows in both the TR and chromosphere due to the upper atmosphere flow of plasma in the form of bundles of spicules or features exhibiting similar spectra. Our analysis suggests that at least subsets of the strong redshifts/downflows observed in TR temperature spectra are due to these bundles of spicules or features exhibiting similar spectra.

On the Response of Transition Region and Corona to Rapid Excursions in the Chromosphere

Date: 2024-05-27
Speaker: Mr. Ravi Chaurasiya
Venue: USO Seminar Hall

Abstract

Spicules are the thin, hair/grass-like structures that are prominently observed at the chromospheric solar limb. It is believed that fibrils and Rapid Blue and Red Excursions (RBEs and RREs; collectively referred to as REs) correspond to on-disk counterparts of type I & type II spicules, respectively. Our investigation focuses on observing the response of these REs alongside similar spectral features in the chromosphere, transition Region (TR), and corona, utilizing space-time plots derived from co-ordinated observations from SST/H-alpha, IRIS, and SDO. Our analysis reveals upflowing REs, promptly reaching temperatures characteristic of the TR and corona, indicating a multi-thermal nature. Similarly, downflowing features exhibiting similar spectral signatures over the disk display plasma motion from the corona to chromospheric temperatures, demonstrating a multithermal nature. In addition to distinct upflows and downflows, we observe sequential upflow and downflow along the same path, depicting a distinctive parabolic trajectory in space-time plots of observations sampling TR and various coronal passbands. Similar to isolated upflows and downflows, these REs also exhibit a multi-thermal nature throughout their trajectory. Furthermore, our results reveal a more intricate motion of the REs in which both upflow and downflow coexist at the same spatial location. On a different note, our analysis, utilizing coordinated IRIS spectral observations, shows spatio-temporal redshifts/downflows in both the TR and chromosphere due to the upper atmosphere flow of plasma in the form of bundles of spicules or features exhibiting similar spectra. Our analysis suggests that at least subsets of the strong redshifts/downflows observed in TR temperature spectra are due to these bundles of spicules or features exhibiting similar spectra.

Propagation and damping of slow magnetoacoustic waves from photosphere to corona along the fan loops rooted in sunspot umbra

Date: 2024-05-21
Speaker: Ms. Ananya Rawat
Venue: USO Seminar Hall

Abstract

Coronal fan loops rooted in sunspot umbra constantly show propagating slow magnetoacoustic waves (SMAWs) of various periods in the corona. However, the origin of these waves found along the whole umbral atmosphere is still unclear. Here, we studied these waves along a clean fan loop system using multi-wavelength imaging and spectroscopic observations from SDO and IRIS. We traced the origin of 3-min waves at the photosphere by utilizing amplitude and frequency modulations of 3-min waves from the corona to the photosphere. This loop tracing also provides the first observational evidence of loop area divergence with height in the umbral atmosphere. We calculated the energy flux of these waves with height in the umbral atmosphere and further obtained the damping lengths of SMAWs propagating along the fan loops to be approx. 208 km and 170 km for 3-min and 1.5-min periods respectively. To investigate the role of area expansion on the damping of these SMAWs, we calculated the total wave energy content within the loop cross-sectional area at each atmospheric height. We further deduced the damping lengths of total wave energy content to be approx. 303 km and 172 km for 3-min and 1.5-min period waves respectively, and thus present the actual damping of SMAWs after taking into account the geometric effect of area expansion of the loops. Our finding highlights the role of loop expansion and frequencies in the damping of SMAWs from the photosphere to corona along fan loops.

Exploring Reconnection in Data-Based MHD Simulations of Solar Flares

Date: 2024-05-13
Speaker: Mr. Satyam Agarwal
Venue: USO Seminar Hall

Abstract

Solar flares are believed to be the manifestation of magnetic reconnection, dissipating magnetic energy in the form of heat, kinetic energy of plasma, and particle acceleration. As a result, the net magnetic energy of the magnetofluid decreases. Further, reconnection changes connectivity of magnetic field lines with respect to the plasma parcels, causing a topological reconfiguration. To explore reconnection and its implications, we perform data-based MHD simulations of flares. In this regard, notable is the use of magnetic field extrapolation for modeling the magnetic field in active-regions. The extrapolated field is utilized as an initial condition for the MHD simulation. In the presence of two contemporary models, namely the nonlinear force-free field (NLFFF) and non force-free field (NFFF), it is imperative to explore the effect of these two varying models on reconnection and consequently on the simulated dynamics of flares. Further, owing to decrease of magnetic energy during flares, the magnetofluid is expected to relax toward an equilibrium of lower energy. Consequently, the simulated dynamics merits interest from the perspective of MHD relaxation theory also. Toward such explorations, we investigate the data-based simulation of solar flares and in this seminar, I will be discussing the results of these studies.

Influence of solar wind medium on the propagation of Earth impacting Coronal Mass Ejections in Heliosphere

Date: 2024-03-20
Speaker: Mr. Sandeep Kumar
Venue: USO Seminar Hall

Abstract

Coronal Mass Ejections (CMEs) are subject to changes in their direction of propagation, tilt, and other properties. We investigated 15 Earth-impacting coronal mass ejections (CME) observed during April 2010 to August 2018 in the Heliospheric Imager (Onboard STEREO) field of view (FOV) to study their propagation in the heliosphere. Out of 15 events, approximately 50 % followed self-similar expansion up to approximately 40 R⊙. Only two events showed significant rotation in HI FOV. The rest of 50 % events showed deflection either in latitude or longitude. This study suggests that CME rotation is not very common in the heliosphere. Our study emphasizes the importance of considering both the ambient magnetic field and solar wind environment to understand the heliospheric propagation of CMEs. The observed deflections and rotations of CMEs can be attributed to a combination of factors, including their interaction with the ambient solar wind, the influence of the ambient magnetic field, and the favorable conditions in the heliosphere required for rotation. These findings contribute to our understanding of the complex dynamics involved in CME propagation and highlight the need for comprehensive modeling and observational studies to improve space weather predictions.

Umbral flashes and their possible association with running penumbral waves

Date: 2024-03-14
Speaker: Mr. Sandeep Dubey
Venue: USO Seminar Hall

Abstract

Sunspots ; being magnetic hotspots ; play a vital role in governing dynamics of the solar atmosphere. Umbral flashes are one of the most dynamic phenomena observed in the sunspot umbral chromosphere. Flashes are observed as small scale intensity enhancements having an approximate periodicity of 3 minutes, interpreted as manifestation of shock developed due to steepening of slow mode waves. Slow mode waves with frequencies above acoustic cutoff frequency get channeled to higher layers of atmosphere along inclined magnetic field lines. Another interesting wave phenomenon observed in sunspot penumbra are running penumbral waves (RPW), appearing as concentric dark and bright rings of disturbances propagating from the umbra-penumbra boundary to edge of penumbra, with a periodicity of 5 minutes approximately. RPWs are also considered as slow mode waves propagating along inclined magnetic fields. In this division seminar; I shall discuss results obtained by analyzing spectroscopic observations of umbral flashes in Ca II 8452 Å line; recorded by narrow-band imager working with the Multi-Application Solar Telescope (MAST). I shall also discuss the aspect of association of running penumbral waves with umbral flashes.

Understanding the Impact of Coronal Mass Ejections on Space Weather: Integrating Observations and Modelling

Date: 2024-02-12
Speaker: Dr. Ranadeep Sarkar
Venue: USO Seminar Hall

Abstract

Coronal mass ejections (CMEs), the most violent eruptive phenomena occurring in the heliosphere, are recognized as one of the major sources for space weather disturbances. CMEs erupt in the form of gigantic clouds of magnetized plasma from the Sun and can reach Earth within several hours to days. If the magnetic field inside an Earth-directed CME or its associated sheath region has a southward-directed north-south magnetic field component (Bz), then it interacts effectively with the Earth’s magnetosphere, leading to severe geomagnetic storms. Therefore, it is crucial to predict the strength and direction of Bz inside Earth-impacting interplanetary CMEs (ICMEs) in order to forecast their geo-effectiveness. Since the magnetic field of solar eruptions cannot reliably be measured via remote means, and direct continuous measurements of the Earth impacting solar transients are routinely available only very close to our planet, modelling of CME magnetic properties is paramount. In this talk, I will present a space weather modelling framework using both analytical and global MHD approaches that could prove to be an operation space weather forecasting tool to predict the geo-effectiveness of CMEs. This talk will also showcase the utilisation of multi-wavelength remote-sensing observations as well as multi-spacecraft in-situ observations at different heliocentric distances to constrain the space weather forecasting models. Further, I will discuss how data obtained from India's space-based solar observatory, Aditya L1 will play a crucial role to enhance our understanding on the CME initiation mechanism.

Multi-line Spectropolarimetry: Our Key to Understand the Solar Atmosphere

Date: 2024-02-06
Speaker: Dr. Rahul Yadav
Venue: USO Seminar Hall

Abstract

Multi-wavelength observations from various telescopes reveal frequent heating and eruptive events in the solar atmosphere, such as Ellerman bombs, UV bursts, jets, surges, and flares. These events not only heat the lower atmosphere (the chromosphere and transition region) but also impact the dynamics of the corona. Despite decades of study, predicting these events and understanding their detailed mechanisms throughout the solar atmosphere remains unclear. Multi-line spectropolarimetric observations spanning different layers of the solar atmosphere are crucial for understanding various aspects of heating events. In this talk, I will discuss how such observations can be used to construct an observationally driven model of heating events using state-of-the-art multi-line inversion methods. Additionally, I will present recent results from the analysis of multi-line spectropolarimetric observations of a C4-class flare observed with the Daniel K. Inouye Solar Telescope. Finally, I will explore the potential for investigating heating events through coordinated observations from the MAST, IRIS, and Aditya-L1 telescopes.

Observations and modelling of coronal mass ejections to understand their space weather effect

Date: 2024-01-04
Speaker: Dr. Ranadeep Sarkar
Venue: USO Seminar Hall

Abstract

Coronal mass ejections (CMEs) are one of the major sources for space weather disturbances. If the magnetic field inside an Earth-directed CME or its associated sheath region has a southward-directed north-south magnetic field component (Bz), then it interacts effectively with the Earth’s magnetosphere, leading to severe geomagnetic storms. Therefore, it is crucial to predict the strength and direction of Bz inside Earth-impacting interplanetary CMEs (ICMEs) in order to forecast their geo-effectiveness. Since the magnetic field of solar eruptions cannot reliably be measured via remote means, and direct continuous measurements of the Earth impacting solar transients are routinely available only very close to our planet, modelling of magnetic properties is paramount. In addition to forecasting the strength of Bz, another significant challenge in space weather prediction involves accurately estimating the arrival time of ICMEs. An in-depth understanding of the initiation mechanism of CMEs is crucial for enhancing our ability to provide extended lead times in predicting when ICMEs will reach Earth. In this talk, I will highlight how data obtained from India's space-based solar observatory, Aditya L1 will play a crucial role to enhance our understanding on the CME initiation mechanism. This talk will also showcase the utilisation of Aditya-L1 data in conjunction with the resources of existing space-based observatories as assets for space weather forecasting. In particular, a space weather forecasting framework will be presented using both analytical and global MHD approaches. Further, I will discuss a recently developed flux-rope model implementation to the global MHD models that could prove to be a major step-forward in forecasting the geo-effectiveness of CMEs.

2023

Multi-instrument studies of solar flares and energetic particles

Date: 2023-12-14
Speaker: Dr. Frederic Schuller and Mr. Malte Victor Philipp Broese
Venue: USO Seminar Hall

Abstract

A Tale of Two Spicules

Date: 2023-12-13
Speaker: Mr. Ravi Chaurasiya
Venue: USO Seminar Hall

Abstract

Spicules are the thin, elongated, hair-like features seen through a high-resolution telescope in chromospheric spectral lines such as H-alpha and Ca II lines. These spicules move upward and downward in the solar atmosphere with velocities ranging between 20 and 150 km/sec. They are believed to carry a mass flux several times greater than that of the solar wind. In this seminar, I will briefly discuss the history and initial development of the spicules and how type II spicules were discovered along the flows associated with these type II spicules in the solar atmosphere.

Phase Shift Measurement of Acoustic Waves in the Lower Solar Atmosphere

Date: 2023-11-24
Speaker: Dr. Hirdesh Kumar
Venue: USO Seminar Hall

Abstract

Solar atmosphere provides a conducive environment for the generation, propagation, mode-conversion, and dissipation of various magnetohydrodynamics (MHD) waves. Acoustic waves are generated by compressibility, whereas the buoyancy-restoring force generates gravity waves. The acoustic waves generated inside the Sun's convection zone are trapped in the acoustic cavities and form standing waves. In the quiet-Sun photosphere, the cutoff frequency is 5.2 mHz, and low-frequency acoustic waves are evanescent. Utilizing the near-simultaneous photospheric and chromospheric line-scan observations in Fe I 6173 A and Ca II 8542 A, respectively, obtained from the Narrow Band Imager instrument installed with the Multi-Application Solar Telescope operational at USO, we have estimated seven height velocities within the Fe I line and nine height velocities within the Ca II line using the bisector method. The analysis of phase shift vs frequency and height shows a non-zero phase shift, indicating the non-evanescent nature of low-frequency acoustic waves in the quiet-Sun. In this talk, I will discuss the possible factors responsible for the non-evanescent nature of low-frequency acoustic waves.

Investigation of Atmospheric Clouds and Boundary Layer over the Western-Indian Region

Date: 2023-10-23
Speaker: Mr. Dharmendra Kumar Kamat
Venue: USO Seminar Hall

Abstract

Atmospheric clouds are crucial in the Earth’s hydrological cycle, radiation budget, and manifest regional and global weather conditions. The formation process of clouds starts in the lowest layer of the atmosphere (known as the Atmospheric Boundary Layer, ABL)and forms at heights ranging from a few hundred meters to several kilometers. Clouds are highly dynamic in space and time, and their proper representation in climate models remains challenging. The true representation of clouds in weather and climate models and a better understanding of physical processes governing cloud formation and dynamics are essential for predicting future climate. This seminar will discuss the cloud processes, cloud-boundary layer interaction, and different techniques for investigating clouds and ABL. Results derived using Lidar observations under the PRL’s Indian Lidar Network (ILIN) Programme over the three western-Indian regions (Ahmedabad, Mount Abu, and Udaipur) will be presented.

How radio techniques can give insights into solar eruptions

Date: 2023-10-20
Speaker: Dr. Anshu Kumari
Venue: USO Seminar Hall

Abstract

The coronal magnetic field (B), the ultimate driver of space weather, plays an essential role in the formation, evolution, and dynamics of the small and large-scale structures in the solar corona. These structures lead to gigantic explosions in the solar atmosphere in the form of large-scale eruptions, such as coronal mass ejections (CMEs), which may severely impact near-Earth space. CMEs are often accompanied by radio emissions, which provide access to observations of the related solar, heliospheric, and ionospheric space weather phenomena. Radio techniques can provide early signatures of particle acceleration associated with solar flares and CMEs. In this seminar, I will talk about state-of-the-art ground and space-based radio instrumentation for solar and space weather studies. Using radio observations and time-dependent data-driven numerical modelling of active regions, I study the formation and eruption of the coronal flux ropes. I will highlight the radio techniques to constrain the initial CME properties close to the Sun and the numerical modelling approach to understand the initiation and evolution of large-scale solar eruptions.

Interplanetary Coronal Mass Ejections

Date: 2023-10-09
Speaker: Ms. Binal Patel
Venue: USO Seminar Hall

Abstract

Interplanetary coronal mass ejections (ICMEs) are interplanetary manifestations of CMEs. ICMEs are essential to study as they are attributed to various space weather phenomena such as solar energetic particle (SEP) events, interplanetary (IP) shocks, and geomagnetic storms, etc. An interesting subset of ICMEs have enhanced magnetic fields (>10 nT) that rotate slowly through a large angle, low proton temperatures, and low plasma Beta; (ratio of the thermal and magnetic field pressure) are called as magnetic clouds. Magnetic clouds are often termed interplanetary magnetic flux ropes (IMFR). There are clear evidences that magnetic clouds are the drivers of intense geomaganetic storms. Hence, understanding the geometry of the magnetic clouds at 1 AU is crucial for analysing their interaction with Earth’s magnetosphere. In this talk, I will discuss the physical connection between the IMFRs at near-Earth enviornment and corresponding CMEs at the near-Sun region by comparing the magnetic field structures of IMFRs and CME source regions. We attempt to identify the flux rope structure in 18 selected events that occurred during Solar Cycle 24 by fitting models with a cylinder and torus magnetic field geometry, both with a force-free field structure. Our results show that the observed flux rope parameters are well reconstructed with the models. The helicity signs of the magnetic clouds remain conserved during their Sun-Earth transit. Our results further support the idea that a flux rope with the main axis parallel to the PIL erupts in a CME, and the erupted flux rope propagates through the interplanetary space with its orientation maintained and is observed as an IMFR.

Mechanical and Electronics design and development of Sun Tracking system for 2m dish antenna.

Date: 2023-08-04
Speaker: Vaibhav Jain, Ketan Agarwal, Hariom, and Yogesh Tailor
Venue: USO Seminar Hall

Abstract

Observations of Solar Corona Using Ground and Space-based Facilities

Date: 2023-07-27
Speaker: Dr. Sasikumar Raja
Venue: USO Seminar Hall

Abstract

Coronal Mass Ejections: From Observations to Simulations

Date: 2023-07-21
Speaker: Dr. Anshu Kumari
Venue: USO Seminar Hall

Abstract

The coronal magnetic field (B), the ultimate driver of space weather, plays an essential role in the formation, evolution, and dynamics of the small and large-scale structures in the solar corona. These structures lead to gigantic explosions in the solar atmosphere in the form of large-scale eruptions, such as coronal mass ejections (CMEs), which may severely impact near-Earth space. CMEs are often accompanied by radio emissions, which provide access to observations of the related solar, heliospheric, and ionospheric space weather phenomena. Radio techniques can provide early signatures of particle acceleration associated with solar flares and CMEs. Using radio observations and time-dependent data-driven numerical modeling of active region, I study the formation and eruption of the coronal flux ropes. I will highlight the radio techniques to constrain the initial CME properties close to the Sun and the numerical modeling approach to understand the initiation and evolution of large-scale solar eruptions. I will also talk about state-of-the-art ground and spaced-based radio instrumentation for solar and space weather studies.

Introduction to Evershed and Inverse Evershed flows

Date: 2023-06-13
Speaker: Mr. Sandeep Dubey
Venue: USO Seminar Hall

Abstract

The Evershed flow is an outflow of plasma in the penumbra of a sunspot, first observed in 1909 by John Evershed at the Kodaikanal Solar Observatory, India. The Evershed effect is observed mainly in photospheric lines. The chromospheric lines such as H-alpha,CaII 8542 present an opposite picture in which an inflow of plasma is observed at chromospheric heights in the solar atmosphere. The inflow of plasma at chromospheric height, known as Inverse evershed flow, is present mainly outside the penumbral region of sunspots. In this talk, I shall introduce the flows with a brief discussion on observations dealing with different physical properties of the flows and models providing a possible mathematical structuring to the flows. I shall also discuss the aspects of these flows that we are working on at present.

Probing the Solar Corona and Solar Wind Using Ground and Space-based Facilities

Date: 2023-05-09
Speaker: Dr. K. Sasikumar Raja
Venue: USO Seminar Hall

Abstract

Ground-based, low-cost low-frequency radio telescopes provide valuable insights into solar transient emissions such as solar flares and coronal mass ejections, and their association with solar radio bursts. Even after decades of intense research on solar radio bursts, we do not thoroughly understand their origin, emission mechanisms, polarisation properties, associated magnetic fields, white light counterparts, association with space weather, and many more. In this presentation, I will discuss the results derived using the observations from various facilities of the Gauribidanur radio observatory, space-based wind/waves, etc. Furthermore, I will discuss solar wind density turbulence and heating rates derived using the Crab Nebula occultation technique. I will also present the way the amplitude of solar wind turbulence, density modulation indices, and proton heating rates vary with the heliocentric distance and solar cycle. Apart from these scientific investigations, I will summarise my contributions to radio instrumentation and the Visible Emission Line Coronagraph (VELC) project. VELC is the internally occulted coronagraph onboard the Aditya-L1 mission, the first Indian mission to explore the Sun and solar corona.

On the chromospheric jets and the associated flows in the solar atmosphere

Date: 2023-05-04
Speaker: Mr. Ravi Chaurasiya
Venue: USO Seminar Hall

Abstract

Chromosphere forms one of the layers of the solar atmosphere sandwiched between the photosphere and the highly structured corona. It is highly complex and dynamic in nature, largely dominated by local magnetic field configuration, associated with spicules, jets, mottles, fibrils, etc. It is believed that they carry mass from the lower atmosphere to the higher atmosphere and are generated due to the leakage of p-mode oscillations or magnetic reconnection. In this seminar, I will talk about jet like structures, particularly spicules observed in the chromosphere, their generation mechanism, and the associated flows as they evolve through the solar atmosphere, using the observations from SST, MAST, IRIS, and SDO/AIA.

Magnetic coupling of sunspot umbral atmosphere

Date: 2023-04-17
Speaker: Ms. Ananya Rawat
Venue: USO Seminar Hall

Abstract

Sunspots host various oscillations and wave phenomena like umbral flashes, umbral oscillation, running penumbral waves, and coronal waves. All the fan loops rooted in the sunspot umbra constantly show a 3-min period propagating slow magnetoacoustic waves in the corona. However, their origin in the lower atmosphere is still unclear. In this work, we studied these oscillations in detail along the clean fan loop system rooted in active region AR12553 for a 4-hour duration on June 16, 2016 observed by Interface Region Imaging Spectrograph (IRIS) and Solar Dynamics Observatory (SDO). We traced the footpoints of several fan loops at different atmospheric heights from the corona to the photosphere. We found presence of 3-min oscillations in the footpoints of all the loops at all the atmospheric heights. We traced the origin of these waves by utilising their amplitude modulation characteristics with time while propagating in the solar atmosphere. We found several amplitude modulation periods, such as 12 min, 22 min, and 35 min of these 3-min oscillations at all heights. Based on our findings, we interpret that 3-min slow magnetoacoustic waves propagating in the coronal fan loops are driven by 3-min oscillations observed at the photospheric footpoints of these fan loops in the umbral region. Results provide clear evidence of magnetic coupling of the solar atmosphere through the propagation of 3-min waves along the fan loops at different atmospheric heights.

Study of Reconnection Dynamics and Plasma Relaxation in MHD simulation of a Solar Flare

Date: 2023-03-27
Speaker: Mr. Satyam Agarwal
Venue: USO Seminar Hall

Abstract

During solar transients such as solar flares and jets, the stored magnetic energy is released explosively in the form of heat and acceleration of the charged particles. The underlying cause of these transients, i.e. the magnetic reconnection process has long been associated with the self-organization or relaxation of magnetized plasmas. In this regard, Taylor's theory (1974) has been investigated quite extensively during the past few decades but a thorough understanding of the relaxation process is still a long way off. While previous studies have focused mostly on analytical magnetic fields, we adopt a novel approach in this study and utilize the data-constrained magnetohydrodynamics (MHD) simulation of an observed solar flare as the governing framework to explore relaxation and to test the predictions of Taylor's theory. The selected active region NOAA 12253 hosts a GOES M1.3 class flare. The investigation of extrapolated coronal magnetic field in conjunction with spatiotemporal evolution of the flare reveals a hyperbolic flux tube (HFT), overlying the observed brightenings. Further, MHD simulation is carried out with the EULAG-MHD numerical model to explore reconnection dynamics. Three distinct sub-volumes are chosen and are subjected to analysis of magnetic field line dynamics along with time evolution of various physically relevant quantities such as magnetic energy, current density, twist, and gradient in magnetic field. In my talk, I will be presenting the theory of self-organization, helicity, MHD relaxation, and Taylor’s relaxation followed by results, summary, and discussion.

Spontaneous generation and annihilation of three-dimensional magnetic nulls

Date: 2023-03-23
Speaker: Mr. Yogesh Maurya
Venue: USO Seminar Hall

Abstract

Three dimensional (3D) magnetic nulls are the location where magnetic field is zero. They are preferential sites for magnetic reconnection and triggering solar coronal transients, for example: solar flares, coronal mass ejections and coronal jets. Such 3D nulls are abundant in solar atmosphere but mechanism of their generation or the reason of their abundance is yet a puzzle. Toward solving this puzzle, the dynamics of an analytical initial magnetic field having an isolated current-free 3D null is numerically simulated with initially prescribed flow. The flow facilitates reconnections, which lead to the generation of primary null pairs in a way that preserves the topological degree. The formation process of these null pairs is novel and different from the standard pitchfork bifurcation. In standard pitchfork bifurcation the additional nulls get created within the current layer developed at the central null. Contrarily, here we found creation of null pairs away from the central null, which we hypothesize is due to the interaction of the imposed flow and the reconnection outflow from the central current layer. Intriguingly, further evolution spontaneously generates new null pairs, which have a novelty by itself. As theorized, these spontaneously generated null pairs also preserve the net topological degree—adding credibility to the simulation. The simulation also shows null pair annihilation. In the talk, I will discuss the results in detail together with the identified mechanism responsible for the generation and annihilation of the nulls.

2022

Observational dynamics of solar atmosphere : Spicules

Date: 2022-12-22
Speaker: Ravi Chaurasiya
Venue: USO Seminar Hall

Abstract

The chromosphere forms one of the atmospheric layers of the solar atmosphere, and it is complex and dynamic in nature, largely dominated by the local magnetic field configuration. Almost all of the mechanical energy that drives solar activity and solar atmospheric heating is converted into heat and radiation within this region. Chromosphere exhibits different dynamic phenomena; one of them is Spicules. In this seminar, I will discuss about spicules, their generation mechanism, properties and how these features can contribute to the mass supplying and coronal heating.

Exploring the source region of 3-min slow magnetoacoustic waves observed in coronal fan loops

Date: 2022-12-09
Speaker: Ananya Rawat
Venue: USO Seminar Hall

Abstract

Sunspots host various oscillations and wave phenomena like umbral flashes, umbral oscillation, running penumbral waves, and coronal waves. All the coronal fan loops rooted in the sunspot umbra constantly show a 3-min period propagating slow magnetoacoustic waves. However, their origin in the lower atmosphere is still unclear. We studied these oscillations in detail along the clean fan loop system rooted in active region AR12553 for a 4-hour duration on June 16, 2016 observed by Interface Region Imaging Spectrograph (IRIS) and Solar Dynamics Observatory (SDO). We traced the footpoints of several fan loops at different atmospheric heights from the corona to the photosphere. We found presence of 3-min oscillations in the footpoints of all the loops at all the atmospheric heights. We traced the origin of these waves by utilising their amplitude and frequency modulation characteristics with time while propagating in the solar atmosphere. We found several modulation periods, such as 11 min, 19 min, and 30-35 min, in both amplitude and frequency modulations of these 3-min oscillations at all heights. Based on our findings, we interpret that 3-min slow magnetoacoustic waves propagating in the coronal fan loops are driven by 3-min oscillations observed at the photospheric footpoints of these fan loops in the umbral region. We also explored any connection between 3-min and 5-min oscillations observed at photospheric footpoints of these loops and found them to be weakly coupled. Results provide clear evidence of magnetic coupling of the solar atmosphere through the propagation of 3-min waves along the fan loops at different atmospheric heights.

Multi wavelength study of solar activities and KASI programs for Heliophysics

Date: 2022-10-20
Speaker: Dr. Kyung-Suk Cho
Venue: USO Seminar Hall

Abstract

Effects of magnetic fields on the propagation of gravity waves in the solar atmosphere

Date: 2022-09-19
Speaker: Mr. Hirdesh Kumar
Venue: USO Seminar Hall

Abstract

Gravity waves in the solar atmosphere are now increasingly recognised as an important contributor to the dynamics and energetics of the lower solar atmosphere. Their characteristic negative phase-shift over height, while propagating energy upwards, is a well recognised observational signature. Since their first detailed observational detection and estimates of energy content, a number of studies have explored their propagation characteristics and interaction with magnetic fields and other wave modes in the solar atmosphere. Recently, numerical simulations have shown that gravity waves are suppressed or scattered and reflected back into the lower solar atmosphere in the presence of magnetic fields. In order to investigate the propagation characteristics, we utilize intensity observations that cover photospheric to chromospheric heights over different magnetic configurations of quiet-Sun (magnetic network regions), a plage, and a sunspot as well as velocity observations within the photospheric layer over a quiet and a sunspot region. We construct two-height intensity - intensity and velocity - velocity cross-spectra and study phase and coherence signals in the wavenumber -frequency dispersion diagrams and their association with background magnetic fields. In this talk, I will discuss the signatures of association between magnetic fields and much reduced phase shifts over height from intensity-intensity and velocityvelocity phase and coherence diagrams both indicating suppression/scattering and reflection of gravity waves by the magnetic fields and thereby provide a qualitativeobservational verification of numerical simulations of such phenomena.

Design of Optical Filters for Solar Observations

Date: 2022-06-23
Speaker: Ms. S. Parvathy
Venue: USO Seminar Hall

Abstract

Propagation characteristics of slow magnetoacoustic waves along coronal fan loops

Date: 2022-03-11
Speaker: Ms. Ananya Rawat
Venue: USO Seminar Hall

Abstract

The upper solar atmosphere i.e, corona (>1 MK) is much hotter than the surface of the Sun i.e, photosphere (<6000 K) which is unexpected according to second law of thermodynamics. To maintain such a high temperature there must be a constant supply of heat/energy to balance the various energy losses. Identification of such atmospheric heating mechanism is one of the major puzzle in solar and stellar physics. Several heating mechanisms have been proposed which are broadly classified into either magnetohydrodynamic (MHD) waves or magnetic reconnection based heating models. In this presentation, focus will be mainly on wave heating mechanism which are further divided into three steps such as generation, propagation, and damping of waves. In this talk, I will present analysis carried out by us to study the evolution and dynamics of propagating intensity disturbances characteristics of waves observed along the clean fan-loop system rooted in active region AR 12553.

The Sun’s Twisted Magnetic Mysteries

Date: 2022-02-18
Speaker: Prof. Lucie Green

Abstract

This talk takes an in-depth look why the Sun produces the most energetic eruptions in the Solar System; events known as coronal mass ejections. Since their discovery in the early 1970s it has been realised that these eruptions occur due to changes in the Sun’s magnetic field. The eruptions appear to be related to a certain magnetic field configuration known as a flux rope. Understanding how and where flux ropes form has unravelled some of the mysteries around coronal mass ejections and understanding their magnetic structure has not only helped explain why these eruptions occur, but also what their space weather impact might be if they are ejected toward the Earth. This talk will explore further the role of the shapes that magnetic fields have in relation to eruptions and introduce a concept known as magnetic helicity. The most recent studies of magnetic helicity have shed new light on how eruptions might be forecast ahead of time. An exciting step forward that might be useful in the years to come for space weather forecasting.

Energy releases and transfer in the solar atmosphere

Date: 2022-01-31
Speaker: Prof. Toshifumi Shimizu
Venue: Online

Abstract

This talk will focus on two topics: results from the first example of ALMA-Hinode-IRIS observations for solar microflares, and the introduction of the future Solar-C (EUVST) mission. Solar microflares are among the major energy input sources to form the active nature of the solar corona. The response of the lower atmosphere to events can provide new clues to investigate dynamical behaviors of microflares. Our Cycle 4 ALMA observation coordinated with Hinode and IRIS satellites allows us to investigate the response. The first half of the talk will discuss what we learned from this novel example of ALMA-Hinode-IRIS observations for solar microflares. The latter half of the talk will introduce our next solar physics mission Solar-C (EUVST), which has been approved for launch in the next 3-4 years. This mission will have a powerful EUV spectroscopic tool to investigate energy releases and energy transfer through the entire outer atmosphere.

2021

Initiation and Driving of Solar Eruptions

Date: 2021-12-10
Speaker: Dr. Bernhard Kliem
Venue: Online

Abstract

An overview will be given of our current knowledge how solar eruptions are initiated and driven, with an emphasis on the eruptive filament/CME component. The Ideal MHD (aka Flux Rope or Loss of Equilibrium) model will be compared with the Reconnecion (aka Arcade) models (primarily the Tether Cutting and Breakout models). This is closely related to the source-region core structure, whose formation will be briefly discussed. Next, I will consider what could lead to confined eruptions instead of CMEs, which is related to the properties of the overlying flux. Partial eruptions will be briefly touched. Finally, some aspects of the numerical modeling of flux rope eruptions will be considered. Here I will show some examples of event modeling that use the active-region model by Titov & Demoulin and examples that use a data-constrained source-region model.

Dr. Arvind Bhatnagar Memorial Lecture 01, The Sun's Magnetic Field and Global Climate Change

Date: 2021-11-17
Speaker: Prof. Sami K. Solanki
Venue: Online

Abstract

The Sun is a restless star. It shows a wide variety of transient or active phenomena, such as dark sunspots, the continuously changing hot corona, energetic flares and immense coronal mass ejections, together with the associated output of energetic radiation and particles. The single quantity that is responsible for the continuing unrest of the Sun is its tangled and dynamic magnetic field. It produces these and many more fascinating phenomena, including variations in the Sun's radiative output or irradiance, which has been invoked as a source of solar influence on the Earth's climate. After an introduction to the Sun and its magnetic field, a short history of solar activity will be given and how that relates to the changing climate on Earth. Finally, the question is considered to which extent the Sun is responsible for the global warming seen in the last century.

Probing Solar and Stellar Physics by Helio- and Asteroseismology

Date: 2021-11-12
Speaker: Prof. Dr. Markus Roth
Venue: Online

Abstract

The Sun and the stars are subject to sound waves that probe their interiors. Observations of these solar and stellar oscillations have emerged as a powerful tool to gain information on the processes inside the Sun and the stars. Through helio- and asteroseismology detailed inferences of the stellar internal structure and of the physical processes inside stars can be obtained. In particular, helioseismology allows studying large-scale flows, sunspots and other magnetic active areas on the Sun. The latter have an important impact on our technological society through potentially harmful solar eruptions. However, a complete understanding of the Sun, and in particular of its magnetism, can only be obtained by understanding the internal structure and properties of the stars in general. Asteroseismology offers the possibilities to address this problem.

The European Solar Telescope: A telescope for the XXI century

Date: 2021-10-22
Speaker: Prof. Manolo Collados
Venue: Online

Abstract

With first light expected at the end of the present decade, the European Solar Telescope (EST) represents the most important technological joint effort made by the European ground-based Solar Physics community. EST will improve considerably the present observational capabilities thanks to its 4-metre diameter. Its optical design is especially designed to study magnetic phenomena taking place in the solar atmosphere, optimising two crucial aspects. On the one hand, its polarimetrically-compensated design is conceived to cancel out the instrumental polarisation induced by the individual elements of the telescope optical train. This property is crucial to detect very small, both spatial and temporal, fluctuations of the magnetic field. Secondly, its design includes a powerful multi-conjugate adaptive optics system (MCAO) to optimally correct the wave-front distortions introduced by the Earth's atmosphere. With this MCAO system, EST is intended to measure the Sun at diffraction limit, with a spatial resolution of 20-30 km and a cadence of few seconds. The design is complemented with the most advanced suite of instruments that will operate simultaneously, to extract the maximum information about the dynamics, thermodynamics and magnetism of the solar plasma at different layers. In this talk, the status of the project will be presented, putting emphasis on the most recent technical developments, the instrumentation and on the scientific goals that will be addressable with this facility.

The Inverse Evershed Flow - Data, Analysis Methods, Results, Physics, Model

Date: 2021-10-17
Speaker: Dr. Christian Beck, National Solar Observatory (NSO), USA
Venue: Online

Abstract

The (inverse) Evershed Flow ((I)EF) was discovered by J. Evershed in 1908 in spectroscopic observations taken at the Kodaikanal Observatory. He found that all photospheric spectral lines in the penumbrae of sunspots showed a persistent pattern of Doppler shifts. On the limb side of the sunspot, the spectral lines were displaced to the blue and on the center side to the red. This "regular" EF can be well explained by a radial outflow away from the umbra at photospheric heights inside the penumbra of sunspots. In all chromospheric lines, the exact opposite pattern was observed with an inflow towards the sunspot in the superpenumbra. The EF has been studied extensively ever since, but corresponding studies of the IEF are rare. In this talk I will present the recent results of our group of a series of studies on the properties of the IEF. We applied a variety of analysis techniques such as bi-sector analysis, thermal or magnetic inversions, magnetic field extrapolations, and a center-to-limb variation study with simplified modeling to high-resolution observations of the IEF. Our results demonstrate that the IEF is a field-aligned flow along magnetic field lines that connect the outer penumbra with the outer end of the moat cell in the form of arched loops. The positive field strength difference and the negative temperature difference between the inner and outer end point induce a flow towards the sunspot through the pressure balance and the siphon flow principle. We find to first order a quantitative agreement of the observed flow speeds and those predicted from the pressure balance equation.

Heating of the solar chromosphere by acoustic waves

Date: 2021-08-20
Speaker: Dr. Michal Sobotka, Astronomical Institute of the Czech Academy of Sciences, Ondrejov, Czech Republic
Venue: Online

Abstract

Acoustic and magnetoacoustic waves play an important role in the chromospheric heating, exhibiting the capability of depositing a main part of their energy in the chromosphere. To study the heating of solar chromospheric magnetic and non-magnetic regions by acoustic and magnetoacoustic waves, the deposited acoustic-energy flux, derived from observations of strong chromospheric lines (Ca II 854.2 nm, H-alpha, H-beta, and Mg II k & h), is compared with the total integrated radiative losses. A set of quiet-Sun and weak-plage regions was observed with the Dunn Solar Telescope (DST), Vacuum Tower Telescope (VTT), Goode Solar Telescope (GST), and Interface Region Imaging Spectrograph (IRIS). The deposited acoustic-energy flux is derived from Doppler velocities observed at two different reference heights corresponding to the middle and upper chromosphere. A set of scaled non-LTE 1D hydrostatic semi-empirical models, obtained by fitting synthetic to observed line profiles, is applied to compute the radiative losses. In the quiet chromosphere, the deposited acoustic flux is sufficient to balance the radiative losses and maintain the semi-empirical temperatures in layers between the two reference heights. In the magnetic active-region chromosphere, the contribution of magneto-acoustic energy flux to the radiative losses is only 10–30 %, too small to balance the radiative losses in the active chromosphere, which has to be heated by other mechanisms.

Triggering of solar eruptions and their large-scale consequences

Date: 2021-07-30
Speaker: Mr. Suraj Sahu, SRF, USO/PRL
Venue: Online

Abstract

Solar eruptions are spectacular magnetic explosions in the Sun’s corona. These explosive events manifest themselves in the forms of filament eruptions, flares, and coronal mass ejections (CMEs) which are collectively termed as solar eruptive events. Decades of studies on these eruptive events have revealed that a common physical process must be the driver mechanism behind all these phenomena. The physical process involves disruption and reconfiguration of the coronal magnetic field, which ultimately leads to an ejection of magnetized plasma. However, even though eruptions have been observed extensively for many years, the specific build-up and trigger mechanisms remain rather elusive. Due to the wide variety of pre-eruptive magnetic configurations, various trigger mechanisms have been proposed. Once the eruption is triggered, it either erupts successfully from the solar atmosphere leading to a CME or contained by the restraining overlying magnetic field to be termed as confined eruption. In this talk, I will discuss about some mechanisms responsible for the triggering of solar eruptions. These works involve extensive analysis using multi- wavelength and multi-instrument solar observations. I will specifically focus on the eruptive features leading to CME. The large-scale aspects in the course of their evolution in the solar corona will also be discussed.

Topological Properties of Three-dimensional Magnetic Null

Date: 2021-07-29
Speaker: Mr. Yogesh Kumar Maurya, JRF, USO/PRL
Venue: Online

Abstract

Three dimensional magnetic null points are one of the potential sites for the magnetic reconnection. They are responsible for the eruptive events like solar flares, jets, coronal mass ejections occurring in the solar corona. In this presentation, the local configurations of three-dimensional magnetic null points are investigated by a linear analysis about the magnetic null point. The configurations are first classified as either potential or non-potential depending on the electrical current as a parameter. Then in non-potential cases the role of the electrical current as a parameter is discussed. In non-potential case the two component of current, one which is parallel to spine determines the spiral nature of field lines near the null while the other component which is perpendicular to the spine affects the inclination of the fan plane to the spine. Further, depending on the sign of real part of the eigenvalue of Jacobian matrix, which is obtained when we do first order Taylor’s expansion of the magnetic field near the null. The sign of the real part of eigenvalues of the Jacobian matrix determines the direction of the field lines. The topological degree is assigned as +1 or -1 depending on the direction of the magnetic field lines of either spine or fan towards the magnetic null point. For an example, if the Magnetic field lines of the spine axes are directed towards the magnetic null point, then the topological degree of magnetic null is +1 and vise-versa. Subsequently, we explore the concept of the net topological degree conservation of three-dimensional magnetic null point in both the cases in ideal as well as in resistive plasma, which can be exploited to understand the sympathetic flaring.

The Secrets of Sunspot Penumbra and a Status Description of the European Solar Telescope

Date: 2021-07-27
Speaker: Dr. Rolf Schlichenmaier, Leibniz-Institut für Sonnenphysik (KIS), Freiburg Germany
Venue: Online

Abstract

I will review our understanding of sunspots confronting theoretical modelling with key observations. Sunspots consist of two distinct stratifactions that are manifested in the photosphere as umbra and penumbra. Only recently, it was found that the photospheric boundary between umbra and penumbra, hitherto defined by an intensity threshold, can be determined with a threshold value for the vertical component of the magnetic field strength (Jurcak 2011). As it turns out, ‘realistic’ sunspot simulation that nicely reproduce the intensity morphology and flow field geometry of observed sunspots (Rempel 2011) fail in reproducing the topology of the magnetic field (Jurcak et al. 2020). At KIS (in collaboration with M. Rempel), we succeeded in setting up intial and boundary conditions that lead to a numerical sunspot model that has the proper photospheric properties, but this leads to another unsolved riddle... In a second part of the talk, I will present the goals and status of the European Solar Telescope. The second edition of the Science Requirement Document was published in the end of 2019 describing the scientific objectives of EST that infer from the main theme to study the fundamental MHD processes of the solar atmosphere at its intrinsic scales. A major recent technical development allows to have the 2nd mirror as an adaptive mirror, which resulted in an optimised optical design of only 6 mirrors (instead of 14 in the old design). I will also address the conceptual design of the EST instrument suite that is currently under way.

Role of magnetoacoustic waves in chromospheric heating

Date: 2021-07-26
Speaker: Mr. Hirdesh Kumar, SRF, USO/PRL
Venue: Online

Abstract

The complete understanding of the chromospheric heating still needs investigation. There are two competing theories that have been proposed to explain the heating of solar atmosphere : (1) mechanical heating by upward-propagating waves (Alfven 1947, Schwarzschild 1948, Stein 1972), and (2) Joule heating associated with the magnetic field reconnection (Parker, 1988) and resistive dissipation of electric currents (Rabin & Moore, 1984). Albeit, some studies have ruled out high frequency (>5.2 mHz) acoustic waves (Fossum & Carlsson, 2005), magnetic reconnection & electric currents (Socas-Navarro, 2005) as being too weak to heat the solar chromosphere. Earlier studies (Jefferies et al. 2006, Rajaguru et al. 2018) show that low-frequency acoustic waves (2-5.2 mHz) can also propagate into solar atmosphere along inclined magnetic fields, and thereby can contribute to the heating of the solar atmosphere. In this talk, I will discuss observational aspects of the propagation of low-frequency acoustic waves into the solar chromosphere in the magnetic network regions using the observations from MAST facility of USO.

CMEs associated with DH type II bursts and their Sun-Earth propagation

Date: 2021-07-20
Speaker: Ms. Binal Patel, SRF, USO/PRL
Venue: Online

Abstract

It is well accepted that the type II solar radio bursts are caused by magneto-hydrodynamic shocks which propagate through the solar corona and interplanetary medium. Type II bursts are associated with flares and coronal mass ejections (CMEs), hence their investigations provide important insights toward understanding the influence of transientsolar activity on the corona and heliosphere. We present the characteristics of decameter-hectometer (DH) type II bursts for the Solar Cycle 23 and 24. For the present study, we have classified the bursts according to their end frequencies into three categories, i.e. Low Frequency Group (LFG; 20 kHz <= f <= 200 kHz), Medium Frequency Group (MFG; 200 kHz < f <= 1 MHz), and High Frequency Group (HFG; 1 MHz < f <= 16 MHz). Our analysis shows a drastic reduction of the DH type II events during Solar Cycle 24 which includes only 35% of the total events (i.e. 179 out of 514). Despite having a smaller number of DH type II events in the Solar Cycle 24, it contains a significantly higher fraction of LFG events compared to the previous cycle (32% versus 24%). However, within the LFG group the cycle 23 exhibits significant dominance of type II bursts that extend below 50 kHz, suggesting rich population of powerful CMEs travelling beyond half of the Sun-Earth distance. Our analysis also indicates that CME initial speed or flare energetics do not have direct link with duration of DHtype II bursts. The profiles relating CME heights with respect to the end frequencies of DH type II bursts suggest that for HFG and MFG categories, the location for majority of CMEs (~65%–70%) is in well compliance with ten-fold Leblanc coronal density model, while for LFG events a lower value of density multiplier (~3) seems to be compatible. We further studied the Sun-Earth propagation characteristics of interplanetary CMEs (ICMEs) arriving at 1 AU that are associated with DH type II radio bursts (type II ICMEs). We provide a detailed comparison of ICME parameters (mean ICME speed, magnetic field) at 1 AU along with Sun-Earth propagation parameters (transit time, acceleration) between the type II and non-type II ICME groups. Our results confirm that the ICME characteristics at 1 AU primarily depend on near-Sun CME characteristics and solar wind conditions in the interplanetary medium. However, to understand complex cases effectively in near-Earth space weather, the analysis needs to be made on a case to case basis and should include the possibilities of CME-CME and CME-corotating interaction region (CIR) interactions.

Solar eruptive event as an Initial Value Problem

Date: 2021-07-06
Speaker: Mr. Satyam Agarwal, JRF, USO/PRL
Venue: Online

Abstract

Coronal magnetic field extrapolations are necessary to understand the magnetic field topology of the source region in solar coronal transients. There are various extrapolation models, broadly classified into non force-free or force-free—depending on whether the model allows for a non-zero Lorentz force or not. Presently, these models are employed to carry out data-driven and data-constrained magnetohydrodynamics (MHD) simulations to explore the underlying magnetic reconnection (MR). It is then imperative to study the dependence of the simulated evolution on the particular extrapolation model used. The focus is that with MRs—a dissipative-process—being responsible for the transients, evolution from two different initial extrapolated fields would not differ since, presumably the dissipation erases the memory. The paper addresses this novel question by comparing numerical simulations of active region NOAA 11977, hosting a C6.6 class eruptive flare, initiated from non force-free and force-free initial fields. For MHD simulations, we employ the EULAG-MHD model which allows for MRs in the spirit of Implicit Large Eddy Simulations (ILESs) while preserving the condition of flux-freezing away from reconnection sites. We find that both the extrapolations yield good agreement with the observed line of sight magnetic field while non force-free field (NFFF) shows a higher degree of correlation with the transverse component compared to non linear force-free field (NLFFF). Nevertheless, broadly, the differences between the two extrapolated fields are not vastly different, except at the neighborhood of three dimensional (3D) magnetic nulls. Further, the topological comparison suggests that most of the magnetic field line structures are reproducible in both the models, although the extent of the agreement between the two varies. Importantly, the MHD simulations suggest the magnetic field lines (MFLs) undergoing MRs evolve similarly, reconnection details being nearly independent of the models—as theorized upfront. Consequently, both extrapolation techniques are suitable for initiating data driven and data-constrained simulations.

Multi-wavelength observations and coronal magnetic field modeling of complex cases of circular ribbon flares

Date: 2021-06-10
Speaker: Mr. Prabir K Mitra, SRF, USO/PRL
Venue: Online

Abstract

Circular ribbon flares are characterized by the circular, quasi-circular or elliptically shaped chromospheric ribbon brightening. Such flares occur from the so-called ‘anemone’ type active regions which are identified by photospheric magnetic configurations where a magnetic patch of one polarity is surrounded by opposite polarity magnetic flux regions. The associated complex coronal arrangement involves a fan-spine configuration in a null point topology. In most of the circular ribbon flares, onset of a set of parallel ribbons are observed prior to the onset of the circular/quasi-circular ribbon brightening that surrounds the parallel ribbons. On the basis of such observations, a general understanding on the circular ribbon flares has been developed; according to which, a flux rope is first developed within the anemone-type active region via the tether-cutting magnetic reconnection. Activation of the flux rope triggers null point reconnection leading to the triggering of the flux rope, a process resembling the coronal breakout at low coronal heights. As a result, we observe the onset of parallel and circular ribbon brightenings sequentially. Our multi-wavelength analysis on circular ribbon flares, complemented by NLFFF extrapolation and associated numerical techniques have provided interesting and important results in this regard. Our studies have revealed that circular flare ribbons can also initiate with the reconnection at the null point, caused by other external factors, that leads to the triggering of the flux rope; resulting in the onset of the circular ribbon brightening prior to the onset of the parallel ribbons. Our analysis has further provided evidence that circular ribbon flares can occur within active regions lacking null points, which can be justifiably considered as a revolutionary idea. In this talk, I will explain the results of our studies on circular ribbon flares and discuss how our new works contribute toward understanding the 3D magnetic reconnection and its role in governing the complex evolution of circular ribbon flares.

Evolution of the complex magnetic structures in AR 12734 using Hall magnetohydrodynamics

Date: 2021-05-20
Speaker: Ms. Kamlesh Bora, SRF, USO/PRL
Venue: Online

Abstract

Hall Magnetohydrodynamics (HMHD) is well known to support faster magnetic reconnection and magnetic field lines (MFLs) evolution having richer complexity compared to its MHD counterpart. In this work, for the first time, we compare data-constrained HMHD and MHD evolution of a solar active region (AR) to explore magnetic reconnections (MRs) triggering a flare by employing numerical simulations augmented with relevant multiwavelength observations. The coronal magnetic field is constructed by employing non-force-free-field (NFFF) extrapolation on the photospheric vector magnetogram.The particular AR under consideration is the AR 12734 during the C1.3 flare on 2019 March 8 around 03:18 UT, followed by a coronal mass ejection (CME). Magnetic structures involved in the flare are identified to be a fluxrope with its overlying MFLs along with a three-dimensional null. Also, the evolution of highly twisted MFLs located beneath its fan and at the middle of a W-shaped flare ribbon are found to be important. Contrary to the MHD simulation, the HMHD simulation shows a higher and faster ascend of the rope along with the overlying MFLs which, further reconnect at a Quasi-separatrix Layer (QSL) located higher up in the corona. The footpoints of the MFLs match better in the HMHD with the central part of a W-shaped flare ribbon visualised on the chromosphere. Additionally, MFLs are found to rotatein a circular pattern in the HMHD whereas no such rotation is seen in the MHD simulation. Interestingly, plasma is observed to be rotating in a collocated chromospheric region which, adds more credibility to the HMHD simulation. Overall, the HMHD simulations are found to agree better with observations and opens up a new avenue to be explored.

On the role of null points and quasi-separatrix layers in magnetic reconnection

Date: 2021-05-13
Speaker: Ms. Sushree Sangeeta Nayak, SRF, USO/PRL
Venue: Online

Abstract

Potential sites of reconnection like null points (where |B|=0) and quasi-separatrix layers (QSLs; regions with sharp change in magnetic field line connectivity) play a major role at the onset of magnetic reconnection and drive the solar transients. However, their simultaneous presence in multiple flux systems makes the process more intriguing to understand the magnetic reconnection in three-dimension. In this direction, the talk will present the results of a set of MHD simulations initiated with both data and analytical boundaries to investigate the impact of null points and QSLs on reconnection in a complex magnetic topological system.

2020

Radio diagnostics of impulsive events on the Sun

Date: 2020-12-22
Speaker: Ms. Sherry Chhabra, New Jersey Institute of Technology & NASA Goddard Space Flight Center, USA
Venue: Online

Abstract

Radio diagnostics hold great importance in exploring strong, impulsive bursts, consequently characterizing the space environment at the Sun, near Earth, and elsewhere in the solar system. In recent years, new instruments have come online that can be used for imaging spectroscopy of the Sun at high temporal, spectral, and spatial resolution. This talk reviews the radio emission that is observed from the Sun during impulsive bursts. Using the data obtained from different radio instruments such as Expanded Owens Valley Solar Array (EOVSA) and Very Large Array (VLA), I will go over a few cases of radio emission at high frequencies and the diagnostics they provide. At lower frequencies, I will discuss in detail, a CME-Associated solar radio event observed by the new instrument Owen Valley Radio Observatory - Long Wavelength Array (OVRO-LWA).

Solar type II radio bursts in the decameter-hectometer wavelength region

Date: 2020-08-25
Speaker: Ms. Binal Patel, JRF, USO/PRL
Venue: Online

Abstract

Type II solar radio bursts are caused by magneto-hydrodynamic shocks which propagate through the solar corona and interplanetary medium. They can be observed as a slowly drifting feature in the dynamic spectra recorded from the ground and space based radio instruments. Type II bursts are associated with flares and coronal mass ejections (CMEs), hence their investigations provide important insights toward understanding the influence of transient solar activity on the corona and heliosphere. Depending on the starting frequency of the radio burst they are classified into three different groups: metric (30 MHz ≤ f ≤ 300 MHz), decameter- hectometer (decameter: 3 MHz ≤ f ≤ 30 MHz, and hectometer: 300 kHz ≤ f ≤ 3 MHz), and kilometric (300 kHz ≤ f ≤ 30 kHz) type II bursts. Out of these groups the decameter-hectometer (DH) domain is of particular interest due to its association with the energetic and wider CMEs that frequently cause space-weather manifestations. The radio bursts in the DH region are observed from Radio and plasma wave experiment (WAVES) on-board Wind spacecraft and SWAVES instruments on-board STEREO spacecrafts. In this talk, I will present the characteristics of DH type II bursts for the solar cycle 23 and 24. The bursts are classified according to their end frequencies into three categories, i.e. High Frequency Group (HFG; 1 MHz ≤ f ≤ 16 MHz), Medium Frequency Group (MFG; 200 kHz ≤ f < 1 MHz), and Low frequency Group (LFG; 20 kHz ≤ f < 200 kHz). We find that the sources for LFG, MFG, and HFG events are homogeneously distributed over the active region belt. Our analysis shows a drastic reduction of the DH type II events during solar cycle 24 which includesonly 35% of the total events (i.e. 179 out of 514). In spite of having smaller number of DH typeII events in the solar cycle 24, it contains a significantly higher fraction of LFG events (34% vs. 23%). This result suggests that cycle 24 is rich in terms of producing CMEs that are able todrive shocks up to larger heliocentric distances in comparison to cycle 23. The profiles relating CME heights with respect to end frequencies of type II bursts suggest that for HFG and MFG categories, the location for majority of CMEs (≈65%-70%) is in well compliance with ten-fold Leblanc coronal density model, while for LFG events a lower value of density multiplier (≈3) seems to be compatible. The properties of the type II associated CMEs and flares will also be discussed for each group in detail for both the solar cycle.

Active region filaments: structure, instability, and eruption

Date: 2020-07-31
Speaker: Mr. Suraj Sahu
Venue: Online Platform

Abstract

Solar filaments are large-scale magnetic structures containing cool and dense plasma suspended in the chromosphere and corona.Filaments form both in active and quiet regions of the Sun; they are classified as active region filaments (ARFs) and quiescent filaments (QFs), respectively. The ARFs are much shorter in length-scale and time-scale in comparison with QFs, yet they undergo dramatic activation and their eruption subsequently leads to solar flares. A fundamental condition governing the formation and development of ARFs is the local coronal magnetic field topology and magnetic flux evolution through the photosphere below. The detailed observations of morphology, evolution, and dynamic processes in disturbed filaments and neighboring coronal magnetic fields during the course of the filament activation may provide clues to understand the onset and energy release mechanisms during the large-scale eruptive phenomena, which have direct impact on space weather. With this motivation, I present studies of filament eruptions from active regions NOAA 12371 and NOAA 12017. Our first analysis deals with the eruptive expansion of an ARF leading to a major solar flare of class M6.6 and a halo, fast CME, which occurred on 2015 June 22. We identify a magnetic flux rope (MFR) along the main polarity inversion line of the active region by employing non-linear-force-free-field modeling of the coronal magnetic field. Our observations reveal that, the MFR is cospatial with an Hα filament and a hot EUV coronal channel. A very remarkable finding of the study lies in the detection of elongated as well as localized HXR sources of energies up to 25 keV that lie exactly over the extended central part of the MFR. This is the first time an activated MFR has been detected in direct HXR observations. In our second ongoing work, we study recurrent homologous eruptions of three filaments leading to major flares of gradually increasing SXR intensities, viz., M2.0, M2.6, and X1.0. We study the evolution of photospheric magnetic field as well as the structural changes in the coronal magnetic configuration during a period of ≈44 hr. We discuss the observed dynamics in the framework of resistive and ideal MHD instabilities.

Wave heating of lower Solar atmosphere

Date: 2020-07-21
Speaker: Mr. Hirdesh Kumar
Venue: Online Platform

Abstract

The complete understanding of the heating of lower solar atmosphere (i.e. chromosphere) still needs investigation. To address the chromospheric heating problem, the following mechanisms have been proposed by solar researchers: (I) mechanical heating by waves (Alfven 1947; Schwarzschild 1948; Narain & Ulmschneider 1996), and (II) Joule heating associated with magnetic field reconnection (Parker 1988) and the resistive dissipation of electric currents (Robin & Moore 1984). In this connection, the analysis of Jefferies et al. (2006) using the low- resolution (~5.2 arcsec/pixel) Doppler velocity observations of photosphere and chromosphere, suggests that the acoustic p-modes (2-5 mHz) which generate inside the convection zone of the Sun can also propagate into the higher solar atmosphere along the inclined magnetic fields and thereby can heat the solar chromosphere by dissipating their energy. However, their observations were insensitive to the signal from small-scale convective cells. In this talk, I will discuss the propagation of low-frequency acoustic waves & their role in the heating of solar chromosphere, along with our planned observations using high resolution (~0.2 arcsec/pixel) chromospheric Ca II 8542 Angstrom Doppler velocity observations obtained from the Multi-Application Solar Telescope (MAST) of USO/PRL in co-ordination with the high resolution (~0.5 arcsec/pixel) photospheric Fe I 6173 Angstrom Doppler velocity observation obtained from HMI instrument aboard SDO spacecraft.

Impact of Hall MHD on Development and Evolution of Magnetic structures during Reconnection

Date: 2020-07-14
Speaker: Ms. Kamlesh Bora
Venue: Online Platform

Abstract

We have extended the well-established magnetohydrodynamic model EULAG-MHD to include the Hall-magnetohydrodynamics. Such an extension is necessary to study a variety of physical systems where the magnetic reconnection scale is of the order of ion inertial scale. Examples of such systems include solar transients, magnetosphere and magnetotail reconnections and laboratory plasmas. The results of two set of simulations using EULAG- HMHD will be discussed in the talk. The first simulation with and without the Hall term is initiated with a sinusoidal magnetic field to benchmark the code. Notably, the magnetic reconnections onset earlier in presence of the Hall term---signifying the reconnections to be faster. Additionally, the Hall term generates magnetic field directed out of the reconnection plane and destroys any inherent symmetry to ultimately make the evolution three dimensional. The resulting three dimensional reconnections develop magnetic flux ropes and magnetic flux tubes. Projected on a plane, the ropes and tubes appear as magnetic islands which with time further breaks into secondary islands and finally coalesce to generate an X-type neutral point. These findings are in agreement with the theory and contemporary simulations of Hall- magnetohydrodynamics, benchmarking the the Hall extension. A novel set of simulations are also executed to explore the activation of a magnetic flux rope from sheared magnetic arcades. Such simulations are instructive to understand solar transients. The results show development of a magnetic flux rope and its ascend as the rope evolves through intermediate complex structures---ultimately undergoing secondary reconnections which locally breaks the flux rope. Interestingly the breakage of the rope occurs earlier in presence of the Hall term, signifying a faster dynamics that leads to magnetic topology favourable for reconnections. We found that the evolution of magnetic field in three dimension is much more complex than their two dimensional idealisation.

Magnetic flux rope eruptions from complex active regions: Initiation and early evolution

Date: 2020-07-09
Speaker: Mr. Prabir K. Mitra
Venue: Online Platform

Abstract

Solar transient phenomena include eruptive filaments, flares, coronal mass ejections (CMEs) etc., which are among the most spectacular and most energetic events occurring in the solar system. Observationally it is established that flares are frequently associated with filament eruptions and CMEs and such flares are called eruptive flares. The ‘standard flare model’ which is also known as the ‘CSHKP model’, considers the presence of a magnetic flux rope (MFR) as a pre-requisite whose activation and upward rising motion is essential for the initiation of a flare. However, the formation and triggering of the MFR is still less understood and has remained a topic of discussion in solar physics. Our multi-wavelength observational analysis, complemented by coronal magnetic field modeling have provided remarkable results on the formation and activation of MFRs in the form of coronal hot channels as well as on the origin of pre-flare activities. Our analysis further reveals that small-scale activities can initiate a series of small-scale activities that lead to a large-scale eruption which is similar to a ‘domino effect’. It is also understood that sufficient storage of magnetic energy can enable even mini-filaments to lead to a CME and large flares, provided overlying magnetic conditions are favorable for eruption. Further, analysis of magnet free energy evolution has provided important information on the capability of active regions to produce powerful eruptive events.

The spontaneous generation of three dimensional magnetic nulls and study of their dynamics during an eruptive event

Date: 2020-06-30
Speaker: Ms. Sushree Nayak
Venue: Online Platform

Abstract

The magnetic null points are well known potential sites of magnetic reconnection in the solar corona. Although their ubiquity in the proximity of coronal transients are thoroughly studied, their generation was unclear in the first place. To investigate this problem, in our work, we have explained two cases analytically, where magnetic null points are generated as the self- organized states towards the end of the magnetohydrodynamic (MHD) evolution followed by repeated magnetic reconnections. The final state of the simulation also shows a conservation of the topological degree in the volume. For a reference, the conservation of topological degree means that the number of positive and negative null points within a volume remains equal irrespective of the system’s dynamics. Alongside this work, we have also explored the dynamics of 3D nulls during an X-class flare associated with a coronal mass ejection (CME) where the eruption mechanism was not straightforward. We have tried to study the change in the topological behaviour and found one 3D null, a set of twisted magnetic field lines and a set of sheared arcades near the vicinity of the flaring region. The dynamics of these complex topologies is then analyzed from the MHD simulation and the process of eruption seems to follow a break-out model scenario. Details of the work will be discussed in the seminar.

Statistical study of radio-loud and radio-quiet Earth-reaching coronal mass ejections and their influence on cosmic ray intensity and geomagnetic storms

Date: 2020-06-25
Speaker: Dr. Hema Kharayat
Venue: Online Platform

Abstract

We present a statistical investigation and geo-effectiveness of Earth-reaching CMEs of solar cycles 23 and 24 in regard to their ability to produce interplanetary DH type II radio bursts during Sun-Earth transit. CMEs associated with DH type II radio bursts are termed as radio-loud (RL) while rest of the CMEs are called radio-quiet (RQ). We further explored the effects of these two CME populations on the variation of cosmic ray intensity (CRI) and occurrence of geomagnetic storm (GS). We found 60% Earth-reaching CMEs as RQ and only 40% as RL. The mean speed of RL CMEs ( 1170 km s^-1) was found to be significantly higher (almost twice) than the mean speed of RQ CMEs ( 519 km s^-1) at near-Sun region while their speed became comparable ( 536 km s^-1 for RL and 452 km s^-1 for RQ CMEs) at near-Earth region. The yearly-averaged speeds of Earth-reaching CMEs follow solar cycle variations. The CRI and geomagnetic Dst index are found to have good negative correlation with speed of Earth-reaching CMEs. RL CMEs were found to be more effective in producing CRI depressions and GSs in comparison to RQ CMEs; in about 70% cases RL CMEs produced CRI depression and GSs earlier than the RQ CMEs. Superposed epoch analysis suggests strongest depression in CRI occurs 2-5 days and 4-9 days after the onset of RL and RQ CMEs, respectively. Further, GS events show a time-lag of 1-5 days and 3-8 days, respectively, with respect to RL and RQ CMEs.

Origin, evolution and space weather consequences of CMEs

Date: 2020-06-03
Speaker: Mr. Ranadeep Sarkar
Venue: Online Platform

Abstract

Development of a Confined Circular-cum-parallel Ribbon Flare and associated Pre-flare Activity

Date: 2020-01-31
Speaker: Ms. Pooja Setia
Venue: USO Seminar Hall

Abstract

Role of active region filaments in triggering solar flares

Date: 2020-01-23
Speaker: Mr. Suraj Sahu
Venue: USO Seminar Hall

Abstract

2019

Machine Learning and its Application in Remote Sensing Data Classification

Date: 2019-12-12
Speaker: Dr. Anil Kumar
Venue: USO Seminar Hall

Abstract

Propagation of Coronal Mass Ejections during Solar Cycles 23 and 24

Date: 2019-12-05
Speaker: Dr. Syed Ibrahim
Venue: USO Seminar Hall

Abstract

Three-dimensional magnetic field structure of a flux emerging region in the solar atmosphere

Date: 2019-11-15
Speaker: Dr. Rahul Yadav
Venue: USO Seminar Hall

Abstract

We analyze high-resolution spectropolarimetric observations of a flux emerging region (FER) in order to understand its magnetic and kinematic structure. Our spectropolarimetric observations in the He I 1083.0 nm spectral region of a FER are recorded with GRIS at the 1.5 m aperture GREGOR telescope. A Milne-Eddington based inversion code was employed to extract the photospheric information of the Si I spectral line, whereas the He I triplet line was analyzed with the Hazel inversion code, which takes into account the joint action of the Hanle and the Zeeman effect. The spectropolarimetric analysis of Si I line displays a complex magnetic structure near the vicinity of FER. Moreover, we find supersonic downflows of 40 km/sec appears near the footpoints of loops connecting two pores of opposite polarity, whereas a strong upflows of 22 km/sec appears near the apex of the loops. Furthermore, non-force-free field extrapolations were performed separately at two layers in order to understand the magnetic field topology of the FER. We determine, using extrapolations from the photosphere and the observed chromospheric magnetic field, that the average formation height of the He triplet line is 2 Mm from the solar surface. The reconstructed loops using photospheric extrapolations along an arch filament system have a maximum height of 10.5 Mm from the solar surface with a foot-points separation of 19 Mm, whereas the loops reconstructed using chromospheric extrapolations are around 8.4 Mm high from the solar surface with a foot-point separation of 16 Mm at the chromospheric height. The magnetic topology in the FER suggests the presence of small-scale loops beneath the large loops. Under suitable conditions, due to magnetic reconnection, these loops can trigger various heating events in the vicinity of the FER.

IRIS2: using representative profiles to invert IRIS Mg II h & k lines

Date: 2019-10-31
Speaker: Dr. Alberto Sainz Dalda, Bay Area Environmental Research Institute, CA USA
Venue: USO Seminar Hall

Abstract

IRIS2: using representative profiles to invert IRIS Mg II h & kline

Date: 2019-10-31
Speaker: Dr. Alberto Sainz Dalda
Venue: USO Seminar Hall

Abstract

The thermodynamics of the solar chromosphere and the transition region (TR) is critical for understanding how the solar corona is energized from the photosphere. The most common method to recover the stratified information in the solar atmosphere is through 'inversion codes' which employ an iterative algorithm to solve the radiative transfer equation for a given model atmosphere by minimizing the difference between the observed and synthetic spectra. Since 2013, NASA's Interface Region Imaging Spectrograph (IRIS) has been providing unprecedented observations of the solar atmosphere from the upper photosphere to the corona, with special attention to the chromosphere and the TR. IRIS is equipped with both spectral and imaging capabilities in several wavelengths spanning the far- and the near-UV domain. In this talk, I will present inversions of the Mg II h&k lines observed by IRIS using the STiC inversion code which considers non-LTE, partial redistribution, and plane-parallel geometry. The results from this code, while being comprehensive of the thermodynamic conditions in the chromosphere, are unfortunately, computationally intensive and expensive. An alternative approach is using the concept of the Representative Model Atmosphere with the STiC inversion code, called IRIS2. The foundation of this novel code is based on easy-to understand, easy-to-use, representative elements obtained with a basic machine learning technique, such as k-mean clustering. This allows us to obtain a depth-stratified model atmosphere from the upper photosphere to the chromosphere in a few CPU-minutes for any IRIS Mg II h&k data set. I will illustrate how the concepts behind this code can be applied to any spectro(polarimetric) data.

Long term study of the Sun using Kodaikanal Digitized data

Date: 2019-09-19
Speaker: Prof. Dipankar Banerjee
Venue: USO Seminar Hall

Abstract

Solar Physics at ARIES Nainital

Date: 2019-09-19
Speaker: Prof. Wahab Uddin
Venue: USO Seminar Hall

Abstract

Long term study of the Sun using Kodaikanal Digitized data

Date: 2019-09-19
Speaker: Prof. Dipankar Banerjee, Indian Institute of Astrophysics Bengaluru
Venue: USO Seminar Hall

Abstract

At the Kodaikanal (KKL) observatory we have four sets of data which consist of While light photoheliograms since 1904, the Ca-K line spectroheliograms since 1906, H-alpha spectroheliograms from 1912 to 1998, and Ca-K spectroheliograms of prominences from 1912 to 1998. All these data are collected with the same instruments with no change in their optics in the last 100 years. Thus, these uniform and contiguous images are extremely valuable to study the long term variations of the Sun over a century. We have recently digitized all these datasets and made them open to the global community through the portal https://kso.iiap.res.in. In this talk I will present a summary of recent science results from this digitized archive.

Magnetoconvective Flows and Waves in the Lower Solar Atmosphere

Date: 2019-08-22
Speaker: Dr. Sangeetha C R
Venue: USO Seminar Hall

Abstract

Solar flares in the context of filament eruptions

Date: 2019-07-26
Speaker: Mr. Suraj Sahu
Venue: USO Seminar Hall

Abstract

Seismic Emission Accompanying Solar Flares

Date: 2019-07-04
Speaker: Mr. Hirdesh Kumar
Venue: USO Seminar Hall

Abstract

Tracking of solar eruptive filaments and finding the temporal connection with associated flare-CME events

Date: 2019-06-03
Speaker: Mr. Suvadip Sinha
Venue: USO Seminar Hall

Abstract

Autonomous generation of three dimensional magnetic nulls

Date: 2019-05-21
Speaker: Ms. Sushree Sangeeta Nayak
Venue: USO Seminar Hall

Abstract

Observationally Constrained Analytical Model for Predicting Magnetic Field Vectors of ICMEs at 1 AU

Date: 2019-05-09
Speaker: Mr. Ranadeep Sarkar
Venue: USO Seminar Hall

Abstract

Solar flares from delta sunspots: Insights from a simulation

Date: 2019-04-22
Speaker: Dr. Piyali Chatterjee
Venue: USO Seminar Hall

Abstract

Multi-wavelength Investigations of Magnetic Reconnection, Triggering and Stability of Solar Eruptions

Date: 2019-03-28
Speaker: Dr. Navin Chandra Joshi
Venue: USO Seminar Hall

Abstract

Daytime Studies of Earth's Upper Atmospheric Behavior Using Multiwavelength Imaging Echelle Spectrograph

Date: 2019-03-20
Speaker: Dr. Deepak Kumar Karan
Venue: USO Seminar Hall

Abstract

The magnetic structure of a flux emerging region in the photosphere and the chromosphere.

Date: 2019-03-18
Speaker: Dr. Rahul Yadav
Venue: USO Seminar Hall

Abstract

The emerging flux region (EFR) at the solar surface shows a complex structure with magnetic bipolar (MBP) fields. The magnetic loops generated in MBPs connect the photosphere and the upper solar atmosphere. The interaction between the loops of opposite direction can trigger various explosive heating events located at different heights of the loop. Thus, their study is crucial in understanding the coupling of the solar atmosphere. An emerging magnetic loop was recorded by GRIS/GREGOR in 1083 nm spectral region, which includes a chromospheric He I triplet and a photospheric Si I line. In this talk, I will discuss how we can extract the magnetic field vector and other physical parameters of the magnetic canopies from the spectropolarimetric observations in He I 1083 nm.

The Development of MFOSC-P : Mount Abu Faint Object Spectrograph-Camera – Pathfinder on PRL 1.2m Telescope.

Date: 2019-03-15
Speaker: Dr. Mudit K. Srivastava
Venue: USO Seminar Hall

Abstract

Mt. Abu Faint Object Spectrograph and Camera-Pathfinder (MFOSC-P) is a fully in house developed instrument on PRL 1.2m telescope at Mt. Abu. MFOSC-P is designed to provide seeing limited imaging in Bessell's B,V, R and I filters over the field of view of ~5X5 arc-min^2. Slit limited resolutions of 2000, 1000 and 500 around 6500, 5200 and 6500 angstroms would be provided using three plane reflection gratings. The instrument has been designed fully in-house including its optical, mechanical, electronics motion control system and user's interface software, while commercially available off-the-shelf ANDOR 1KX1K CCD camera system is used as the detector. MFOSC-P has seen telescope first light in February 2019 very successfully and has been successfully verified for its imag/spectrum quality. We shall be discussing various design and development aspects of MFOSC-P in the talk.

Role of Hall-MHD in coronal magnetic reconnection.

Date: 2019-02-26
Speaker: Ms. Kamlesh Bora
Venue: USO Seminar Hall

Abstract

Triggering and evolution of the largest solar flare of solar cycle 24

Date: 2019-02-13
Speaker: Mr. Prabir Kumar Mitra
Venue: USO Seminar Hall

Abstract

Properties of Chromospheric Magnetic Field of Sunspots

Date: 2019-01-22
Speaker: Dr. Jayant Joshi
Venue: USO Seminar Hall

Abstract

The photospheric structure of magnetic field of sunspots has been studied extensively in the last few decades through Zeeman diagnostics of various magnetically sensitive spectral lines. Observation of magnetic field in the chromosphere is much more challenging than that in the photosphere. Therefore, the chromospheric magnetic field of sunspots has remained lesser explored. In addition to understanding three-dimensional structure of sunspots, knowledge of the chromospheric magnetic field is very essential for understating the small scale transient events in sunspots, e.g. ,penumbral micro-jets, transition region penumbral bright dots, and chromospheric oscillations. Using ground based telescopes, 1.5-meter GREGOR telescope and Swedish 1-meter Solar Telescope (SST), different aspects of chromospheric magnetic field of sunspots have been explored. In this seminar, I will focus on the fine-structure of magnetic field in a sunspot penumbra in the upper chromosphere. I will also present results from our recent study on the chromospheric magnetic field variations associated with umbralflashes and running penumbral waves.

2018

Advances and Challenges in Space Plasma Modelling and Its Application to Space Weather Forecasting

Date: 2018-12-18
Speaker: Dr. Bhargav Vaidya
Venue: USO Seminar Hall

Abstract

Numerical simulation, which provides a natural bridge between theory and observations, is an essential tool for understanding complex plasma behaviour. Space plasma modelling typically span a tremendous scale of densities and temperature with scales ranging ten orders of magnitude in space and time. Additionally, multiple processes developing at the electron, ion and global scales strongly interact with each other. For example, processes like supersonic shocks, magnetic reconnection and turbulence play a very crucial role at these different scales and significantly alter the structure of space plasma. These physical phenomena are also responsible for acceleration of particles to very high energies. I will describe our recent development of an hybrid framework with PLUTO code to study space and astrophysical plasmas at various scales. As a potential application to this novel framework, I will present some the very recent and ongoing work on space weather forecasting. Developing prediction models for space weather has lately come into tremendous focus within the space science community. The key ingredient to develop such a model requires a detailed understanding of the magnetic activities on the Sun, formation of CMEs and associated high energy particles, propagation of CME shocks through the heliosphere and finally its impact on Earth's magnetosphere. In this talk, I will review recent advances in developing a numerical framework for space weather forecasting. Further, I will also outline some of the challenges that the space plasma modelling community is facing today and in the future.

Complex Evolution of Magnetic Helicity in Active Regions

Date: 2018-12-06
Speaker: Dr. B. Ravindra
Venue: USO Seminar Hall

Abstract

Active regions on the Sun emerge on different scales, latitudes and time of the solar activity. These active region magnetic fields are believed to be generated through dynamo action at the shear layer located beneath the convection zone. These magnetic fields are concentrated into flux tubes which rise through the convection zone and form bipolar sunspots at the photosphere. The simulations show that magnetic fields emerge from the photosphere with a twist. Some of the active regions show more twist than the others. The twists in the active regions are measured through a quantity called magnetic helicity. With the available long time sequence of magnetograms, several studies have been reported in the literature about the measure of helicity flux density in active region coronae. In this talk, I will discuss the components of helicity flux measured through the partitioning of the magnetograms into a set of unipolar regions; the methodology adapted for the magnetograms partitioning; the magnitude of the helicity flux components and its application to rotating and emerging sunspot regions.

Solar Wind Density Turbulence from 2 to 45 Rsun

Date: 2018-11-28
Speaker: K. Sasikumar Raja
Venue: USO Seminar Hall

Abstract

Various types of remote sensing observations have been used so far to probe the weakly compressible density turbulence in the extended solar corona and solar wind. Using the angular broadening observations of radio celestial point like sources, we have studied various turbulent parameters in the solar wind: anisotropic broadening, amplitude of density turbulence, density fluctuations, proton heating rate and the dissipation scales. For this study, we used the observations of Gauribidanur radioheliograph, Very Large Array and other historical observations carried out during 1952-2017. In this talk, I will discuss, the way these parameters vary with heliocentric distance and the solar cycle. The newly launched Parker Solar Probe and upcoming Solar Orbiter missions are going to play a crucial role in understanding long standing mysteries of the solar wind. Apart from these, I will briefly discuss the CALLISTO spectrometer which we have recently installed at IISER Pune to monitor the transient radio emissions from the solar corona.

Type II radio bursts, coronal mass ejections and geoeffectiveness

Date: 2018-11-16
Speaker: Dr. A. Shanmugaraju
Venue: USO Seminar Hall

Abstract

Solar Radio Astronomy "CALLISTO instrument and the e-Callisto network"

Date: 2018-10-04
Speaker: Mr. Christian Andreas Monstein
Venue: USO Seminar Hall

Abstract

Propagation characteristics of Coronal Mass Ejections

Date: 2018-09-18
Speaker: Mr. M. Syed Ibrahim
Venue: USO Seminar Hall

Abstract

Propagation characteristics of Coronal Mass Ejections (CMEs) are very important in the concept of space weather studies. In this presentation, I want to discuss three published works; these papers are published during my PhD. First, we tried to understand the CME propagation differences between the rising phase of solar cycles 23 and 24. Second, we analyzed the relationship between CME initial parameters and corresponding Geo-effectiveness (i.e. Dst, geomagnetic storm disturbances index). Using these relationships, we developed empirical equations for Dst forecasting with the function of CME initial parameters. Finally, we predicted ICME arrival times for four major Geo-effective CMEs during the rising phase of solar cycle 24 using Empirical CME Arrival model (ECA), and these estimated arrival times are compared with the observational results.

Evolution of Coronal Cavity from Quiescent to Eruptive Phase in Association with Coronal Mass Ejection

Date: 2018-08-07
Speaker: Mr. Ranadeep Sarkar
Venue: USO Seminar Hall

Abstract

The initiation mechanism of coronal mass ejections (CMEs) remains among the most elusive topics in solar physics. The initiation and triggering of CMEs can be studied by observing the coronal cavities in the lower coronal regions. These cavities appear as dark features and are believed to be the density depleted cross-sections of the magnetic flux ropes, where the magnetic field strength attains a much higher value compared to the background corona. Cavities may last for days or even weeks and evolve as the dark core part of the CME during the eruptive phase. In order to understand the pre-eruptive stability conditions for quiescent cavities and the triggering mechanisms for those structures to erupt, it is important to study the morphological evolution of the coronal cavities. In this work, we study the evolution of a cavity in lower corona using the observations from STEREO SECCHI/EUVI and PROBA2/SWAP EUV imager. In the quiescent phase, the cavity centroid height slowly rises from 1.10 to 1.23 RS during its passage on the visible solar disc from May 30 to June 13, 2010 and its initial circular shaped morphology gradually expanded and evolved into elliptical shape prior to the eruption from the western solar limb. The extended field-of-view of SWAP fills the observational gap between 1 to 2 RS. It enables us to capture the complete evolution of the erupting cavity starting from its EUV counterpart in the lower corona up to the white light cavity morphology seen in LASCO C2/C3 field-of-view. During the eruptive phase, we have observed a significant non-radial motion of the cavity at a very low coronal height of 1.3 RS. Furthermore, the geometrical fitting to the cavity morphology in different time-steps during its eruptive phase reveals that it exhibits non self similar expansion in the lower corona. We also discuss the role of the background magnetic field and the possible instabilities which may lead to the non-radial motion and initiation of the cavity eruption respectively.

Study of multi-wavelength emissions from solar flares

Date: 2018-07-16
Speaker: Mr. Prabir Kumar Mitra
Venue: USO Seminar Hall

Abstract

Caused by magnetic reconnection and a sequence of subsequent physical processes, huge amount of energy is radiated over the entire electro-magnetic spectrum during solar flares. Multi wavelength observation and analysis are extremely important to understand the different physical processes during flares, which occur at different layers of the Sun (i.e., Photosphere, Chromosphere, Corona). During September 4-10, 2017, an active region (NOAA 12673) became very active and produced a series of many large flares (27 M-class and 4 X-class) including the largest flare in the solar cycle 24 which occurred on September 6, 2017. We have analyzed the evolution of the active region during the aforementioned time interval and conducted a multi-wavelength study of the homologous X-class flares on September 6, 2017.

Magnetic reconnection in solar corona

Date: 2018-07-12
Speaker: Ms. Sushree Sangeeta Nayak
Venue: USO Seminar Hall

Abstract

Rearrangement in the magnetic field configuration due to the fundamental process called magnetic reconnection accompany eruptive phenomena like flares and coronal mass ejection in the solar atmosphere. There are different potential sites of magnetic reconnection in both 2D (X-type, Y-type, and O-type)and 3D(Spine -fan configuration and quasi-separatrix layers). These configurations are ubiquitous in the solar corona and are also proved to be responsible for dynamics observed there. In this talk, I will discuss the aforementioned structures which are constructed numerically from the photospheric field. For the purpose of the understanding of the involved dynamics, I will also present their magnetohydrodynamics evolution.

Coronal magnetic field extrapolation techniques

Date: 2018-07-03
Speaker: Ms. Kamlesh Bora
Venue: USO Seminar Hall

Abstract

The most magnificent and dangerous indication of solar activity, flares and coronal mass ejections (CMEs), occur in the solar corona, and are believed to be powered by free magnetic energy stored in the coronal magnetic field. Modeling and measurement of the coronal magnetic field have been urgent targets of solar physics for many years. We have studied extrapolation techniques: potential or current-free, linear force-free, and non-force-free respectively. For this purpose we choose vector magnetogram of AR12673 on 06-09-2017 at 11:48UT from HMI/SDO. We have also developed codes for potential and linear force-free extrapolations. We compared the field line topology over and near the polarity inversion line(PIL) and noted that EUV brightenings in 131 and 304 angstrom channel along with vector magnetogram matches exactly with non-force-free extrapolation. We have found a 3-D null point using linear force-free technique over the PIL where the flare took place.

Magnetohydrodynamic simulation of magnetic null-point reconnections in NOAA AR12192 initiated with an extrapolated non-force-free-field

Date: 2018-05-08
Speaker: Dr. Avijeet Prasad
Venue: USO Seminar Hall

Abstract

Magnetohydrodynamics of the solar corona is simulated numerically. The simulation is initialized with an extrapolated non-force-free magnetic field using the vector magnetogram of the active region (AR) NOAA 12192 obtained on the solar photosphere. Particularly, we focus on the magnetic reconnections occurring close to a magnetic null-point that resulted in appearance of circular chromospheric flare ribbons on October 24, 2014 around 21:21 UT, after peak of an X3.1 flare. The extrapolated field lines show the presence of the three-dimensional (3D) null near one of the polarity inversion lines, where the flare was observed. In the subsequent numerical simulation, we find magnetic reconnections occurring near the null point, where the magnetic field lines from the fan-plane of the 3D null form a X-type configuration with underlying arcade field lines. The footpoints of the dome-shaped field lines, inherent to the 3D null, show high gradients of the squashing factor. We find slipping reconnections at these quasi-separatrix layers, which are co-located with the post-flare circular brightening observed at the chromospheric heights. This demonstrates the viability of the initial non-force-free field along with the dynamics it initiates. Moreover, the initial field and its simulated evolution is found to be devoid of any flux rope, which is in congruence with the confined nature of the flare.

Inferences of the Deep Solar Meridional Flow

Date: 2018-03-01
Speaker: Dr. Vincent Boening
Venue: USO Seminar Hall

Abstract

The solar meridional flow is a crucial ingredient in modern dynamo theory. Seismic estimates of this flow have, however, been contradictory in deeper layers. Here, we develop and validate a method for computing spherical Born approximation kernels for time-distance helioseismology and we employ these kernels to invert for the deep solar meridional flow using 652 days of GONG data from 2004 - 2012. Above about 0.85 solar radii, our inversions confirm the result obtained by Jackiewicz et al. with the ray approximation regarding the general structure of the flow. This especially concerns a shallow return flow at about 0.9 solar radii, although some differences in flow magnitude are apparent. Below about 0.85 solar radii, we obtain several different results that are consistent with the measured travel times within the measurement errors. While one result is similar to the original single-cell flow found by Jackiewicz et al., the other results exhibit a multi-cell flow structure in the southern hemisphere. To reach an unambiguous conclusion on the meridional flow in this region, the errors in the measured travel times have to be considerably reduced. From this, I conclude that an unambiguous detection of the meridional flow is limited to a much shallower region than previously thought. This is a partial relief to the controversy about measurements of the deep solar meridional flow.

Long-term Trends in Solar Photospheric Fields and Solar Wind Micro-Turbulence

Date: 2018-02-27
Speaker: Prof. S. Ananthakrishnan
Venue: USO Seminar Hall

Abstract

Solar activity has been monotonically decreasing over the past ~ 25 years with each new solar cycle being less active than the previous one. What could this mean in the near term period? We will explore this aspect based on photospheric and heliospheric data.

A very low frequency space-payload to study interplanetary plasma turbulence

Date: 2018-02-27
Speaker: Prof. S.Ananthakrishnan
Venue: USO Seminar Hall

Abstract

At the S.P.Pune University, we are making an effort to put a small tri-axial electric and magnetic space payload in the frequency range from 0.3 to 16 MHz, called SEAPS (Space Electromagnetic And Plasma Sensor) into a L1 or Lunar orbit with multiple objectives. It will serve as a training effort for the University students, as a technology demonstrator and as a tool to investigate the lowest radio frequencies hitherto unopened, to understand solar flares and reconnection mechanisms, as a precursor for a future interferometric mission, etc. We will give a brief description of the efforts.

Filament Dynamics on Small to Moderate Scales

Date: 2018-02-26
Speaker: Dr. Anand D. Joshi
Venue: USO Seminar Hall

Abstract

Sunspot and synoptic science at the World Data Center SILSO

Date: 2018-02-26
Speaker: Dr. Frédéric Clette
Venue: USO Seminar Hall

Abstract

Since 1940, the solar physics team of the Royal Observatory of Belgium has developed a solar station dedicated to synoptic observations of the Sun (photosphere and chromospere). Since 1981, it also runs the World Data Center (WDC) for the sunspot index, a unique 400-year record of solar activity, further expanding its expertise in the long-term monitoring of the solar cycle. We present the evolution and the present capabilities of the Uccle station (USET) and the ongoing digitization of its sunspot drawing and photographic collections. Our production include both near real-time CCD images of the Sun and a new detailed sunspot group catalog covering more than 70 years. Next to our own observations, we also present the recent deep modernization of the WDC SILSO. In particular, we describe the recent end-to-end recalibration of the sunspot and group number series, which led to the release of the first-ever revised version of this unique reference. >From a static data set, the sunspot number has now evolved towards a dynamical data series open to continuous improvements and quality control, back to year 1610. We conclude on our future plans for synoptic ground-based imaging at USET, in coordination with other stations worldwide, and on the continuing improvement to the sunspot number. We will evoke the current and future implications of those new long-term datasets on key scientific issues in solar physics and other disciplines.

2017

The study of different extrapolation techniques

Date: 2017-07-28
Speaker: Ms Sushree Sangeeta Nayak
Venue: USO Seminar Hall

Abstract

The topological changes in the magnetic field are believed to be the driver of eruptive phenomena like flares and coronal mass ejections occurring in the solar corona. Currently, only the measurements of the photospheric vector magnetic field are available with high cadence and high resolution through various space- and ground-based telescopes. The coronal field is typically inferred by assuming an equation of state for the magnetic field such as the: potential field, linear force-free field (LFFF), non-linear force-free field (NLFFF) and non-force-free field (NFFF). In order to check the viability of these fields in describing the coronal dynamics, we extrapolate the photospheric vector magnetic field for the active region 11158 on 14th February 2011, using all the four above mentioned extrapolation techniques and compare their respective field topologies. Interestingly, these fields can also be utilized as suitable initial magnetic fields to explore the magneto hydrodynamic evolution of the active region.

Photospheric changes leading to solar eruptions

Date: 2017-07-13
Speaker: Mr. Ranadeep Sarkar
Venue: USO Seminar Hall

Abstract

Astrophysical coronae: from sun to galaxy clusters

Date: 2017-06-06
Speaker: Dr. Prateek Sharma
Venue: USO Seminar Hall

Abstract

Magnetohydrodynamic Modeling of Solar Coronal Dynamics with an Initial Non-force-free Magnetic Field

Date: 2017-04-27
Speaker: Dr. Avijeet Prasad
Venue: USO Seminar Hall

Abstract

Magnetic fields and waves in the lower solar atmosphere, and difficulties in local helioseismology

Date: 2017-04-06
Speaker: Prof.S.P. Rajaguru
Venue: USO Seminar Hall

Abstract

Paschen-Back effect in atomic states as a tool for magnetic field diagnostics

Date: 2017-02-07
Speaker: Sowmya K.
Venue: USO Seminar Hall

Abstract

Exploration of the second solar spectrum through polarimetric studies

Date: 2017-01-17
Speaker: Ms. Supriya H D
Venue: USO Seminar Hall

Abstract

Forces governing CME propagation

Date: 2017-01-13
Speaker: Prof. Prasad Subramanian
Venue: USO Seminar Hall

Abstract

2016

Hot flux ropes observed by SDO

Date: 2016-06-16
Speaker: Aparna V. Sastry
Venue: USO Seminar Hall

Abstract

Study of Evolution of Magnetic Inhomogeneities on The Sun Using Narrow Band Imaging

Date: 2016-05-04
Speaker: Mr. Sajal Kumar Dhara
Venue: USO Seminar Hall

Abstract

Latest developments in space weather forecast by means of ground- based facilities

Date: 2016-02-15
Speaker: Prof. Robertus Erdelyi and Team
Venue: USO Seminar Hall

Abstract

Space Weather research in HVAR Observatory

Date: 2016-02-02
Speaker: Mateja Dumbovic
Venue: USO Seminar Hall

Abstract

Solar Polarimetry

Date: 2016-01-20
Speaker: Sankarasubramanian
Venue: USO Seminar Hall

Abstract

2015

Topic: Solar observations with MWA

Date: 2015-12-18
Speaker: Divya Oberoi
Venue: USO Seminar Hall

Abstract

Energisation of particles from magnetic reconnection

Date: 2015-12-18
Speaker: Rohit Sharma
Venue: USO Seminar Hall

Abstract

The Solar Corona is fascinating. Coronal heating requires either a mechanism to transport heat to the corona or to generate heating in the corona, or both. Currently, the magnetic reconnection process is believed to be the dominant heating mechanism. Here we explore the energy dissipation in magnetic reconnection in small resistivity limits under the magnetohydrodynamics approximation. In addition, we also ask the question - how does the dissipated energy manifest itself ? To study this, we examine the dynamics of test charged particles at the site of magnetic reconnection. We focus on acceleration and formation of particle beams. The talk will summarise initial results from this study.

Library's Role in facilitating Research

Date: 2015-10-14
Speaker: Dr. Nishtha Anilkumar
Venue: USO Seminar Hall

Abstract

Intensity correlation and spatial modes of light

Date: 2015-09-29
Speaker: Prof. R.P. Singh
Venue: USO Seminar Hall

Abstract

Intensity correlations, first explored by Hanbury Brown and Twiss in Astronomy, have played an important role in understanding the nature of light. Starting with sizing of stars to understanding the phase transitions and folding of protein molecules, it has found numerous applications in different fields of science. After introducing this versatile technique we will discuss how it can be used to discriminate different spatial modes of light. Some possible applications to solar physics will also be discussed.

COMESEP: Space Weather Forecasting tool

Date: 2015-09-21
Speaker: Prof. Nandita Srivastava
Venue: USO Seminar Hall

Abstract

Estimation of thermal and non-thermal energies using X-ray measurements during impulsive phase of a failed solar eruption

Date: 2015-09-21
Speaker: Upendra Kumar Kushwaha

Abstract

Statistical properties of Umbral Dots

Date: 2015-09-21
Speaker: Rahul Yadav
Venue: USO Seminar Hall

Abstract

MHD simulations of flux rope formation & loop contraction

Date: 2015-09-21
Speaker: Sanjay Kumar
Venue: USO Seminar Hall

Abstract

Interplay of large and small scales: solar corona

Date: 2015-09-21
Speaker: Dr. R. Bhattacharyya
Venue: USO Seminar Hall

Abstract

Solar physics at USO during its formative years

Date: 2015-09-21
Speaker: Prof. Ashok Ambastha
Venue: USO Seminar Hall

Abstract

Engineering interface to MAST project

Date: 2015-09-21
Speaker: Naresh Jain
Venue: USO Seminar Hall

Abstract

Imaging Spectro-Polarimeter for MAST

Date: 2015-09-21
Speaker: Alok Ranjan Tiwary
Venue: USO Seminar Hall

Abstract

Compensation of MAST alignment errors during operation: Influence matrix of M2-Hexapod

Date: 2015-09-21
Speaker: Dr. A. Raja Bayanna
Venue: USO Seminar Hall

Abstract

Present status of MAST

Date: 2015-09-21
Speaker: Prof. Shibu K. Mathew
Venue: USO Seminar Hall

Abstract

Milne-Eddington inversion code forFe-I 6173.33 nm spectral line

Date: 2015-08-24
Speaker: Rahul Yadav
Venue: USO Seminar Hall

Abstract

Inversion techniques are the most powerful and sophisticated tool to infer the magnetic and thermodynamical properties of the solar atmosphere from the interpretation of Stokes profiles. The basic idea of any inversion code is to iteratively fit the observed Stokes profiles with the synthetic profiles. The synthetic profiles are generated by solving the polarised radiative transfer equation (RTE) which assumes a model atmosphere. After optimizing the merit function, the best fit model atmosphere is inferred as the model of the atmosphere. We are developing an inversion code of the radiative transfer equation in Milne-Eddington (ME) approximations. Under ME assumptions the properties of the solar atmosphere are constant with height, except the source function which depends linearly on optical depth. A standard Levenberg-Marquardt least-square minimization method is used to optimize the merit function. The new ME-code, written in IDL, can be used for any photospheric spectral line. To facilitate the comparison, we selected MERLIN inversion code which is a standard inversion code used to invert the spectro-polarimetric data from Hinode. The inversion strategy of the new ME-code, comparison between new ME-code and MERLIN will be discussed in this talk.

Introduction to polarimetry

Date: 2015-08-06
Speaker: Alok Ranjan Tiwary
Venue: USO Seminar Hall

Abstract

MHD relaxation in astrophysical plasmas

Date: 2015-07-23
Speaker: Sanjay Kumar
Venue: USO Seminar Hall

Abstract

Imaging polarimeter for Multi Application Solar Telescope

Date: 2015-07-21
Speaker: Alok Ranjan Tiwary
Venue: USO Seminar Hall

Abstract

The Multi‐application Solar Telescope (MAST) is a 50 cm off‐axis Gregorian telescope installed at the lake site of Udaipur Solar Observatory. One of the scientific objectives of MAST is to study the evolution of vector magnetic field on the solar atmosphere and its connection to various solar activities. In order to measure the vector magnetic field in the solar atmosphere, we have developed a Polarimeter for the MAST, which will be used for precise measurements of the Stokes vector at two different wavelengths i.e. at 617.3 nm and 854.2 nm, corresponding to photospheric and chromospheric heights, respectively. The Polarimeter will modulate the polarization signal using two liquid crystal variable retarders (LCVR) along with a linear polarizer (one set each for the above wavelengths).

Speckle imaging with masked apertures: application to solar imaging

Date: 2015-05-20
Speaker: Dr. R. Sridharan
Venue: USO Seminar Hall

Abstract

Particles and fields in the solar system

Date: 2015-02-23
Speaker: Prof. Daniel N. Baker
Venue: USO Seminar Hall

Abstract

Even before the official dawn of the Space Age – that is, the launch of the Sputnik and Explorer spacecraft in 1957-1958 – many investigators around the world were engaged in space physics research. Using rockets to get to the fringes of outer space, early researchers made pioneering observations of the Sun and Earth’s upper atmosphere. This talk will recount some of the earlier history of contributions to Sun-Earth (“solar terrestrial”) studies. A principal focus of the talk will be the modern studies of energetic particles and electromagnetic fields in Earth’s cosmic neighbourhood. From a rather personal perspective, my Laboratory for Atmospheric and Space Physics (LASP) has been playing an increasingly prominent role in forefront studies of Earth’s “magnetosphere” and LASP researchers are using this core terrestrial knowledge to advance planetary and astrophysical understanding as well. Moreover, study and understanding of the space environment of Earth is absolutely essential for our knowledge of “space weather” which represents a major threat to our modern technological society. The presentation will address all these aspects and will conclude with a look forward to future solar system programs and opportunities.

2014

Estimation of Solar EUV flux rate during Strong, Mid and Weak Solar flares using GPS satellite data

Date: 2014-12-19
Speaker: Mr. Talwinder Singh
Venue: USO seminar room

Abstract

Correlation of Solar Extreme Ultraviolet (EUV) photon flux rate in 26-34 mm spectral band during Solar flares will be shown with a GNSS Solar Flare Activity Indicator (GSFLAI) which is defined as the gradient of ionospheric Vertical Total Electron content rate vs. cosine of Solar Zenith Angle in day hemisphere. GSFLAI is measured from data collected by global network of dual frequency GPS receivers. Extreme ultraviolet photon flux data in 26-34 nm range was obtained from SEM instrument onboard SOHO spacecraft. GSFLAI for 60 X class flares, 320 M class flares and 300 C class flares occurred since 2001 was directly compared with EUV Solar flux rate data to show the correlations. It was found that GSFLAI and EUV flux rate have a linear relationship for all class of flare hence showing that the data from global network of GPS receivers to be a potential proxy for direct measurements of Solar EUV photon flux.

Adaptive Optics and its applications in vision research

Date: 2014-12-02
Speaker: Krishnakumar Venkateswaran
Venue: USO seminar room

Abstract

A possible solution towards overcoming earth?s atmospheric turbulence aimed at providing high resolution astronomical images using ground based telescopes came through the advent of adaptive optics (AO). An AO system consists of a wavefront sensor to measure the optical distortions in the wavefront and an optical element to compensate the optical distortions. In 1953, Babcock proposed a method for compensating earth?s atmospheric turbulence but it was not until 1977 when Hardy and colleagues successfully demonstrated the use of AO in astronomy. Initially used for military purpose, AO made inroads in astronomy and is now being used almost as a staple part of any high resolution optical imaging system in astronomical telescopes. Liang et. al. (1992, 1994) was the first to demonstrate the use of a Shack Hartmann wavefront sensor to measure the monochromatic aberrations in the eye. Later, the AO group at the University of Rochester incorporated the wavefront sensor into adaptive optics ophthalmoscope (Liang et al., 1997). Roorda et al., (2002) combined conventional scanning laser ophthalmoscope and AO (Adaptive Optics Scanning Laser Ophthalmoscope ? AOSLO) correcting for both lower and higher order aberrations to obtain images with unprecedented lateral resolution resolving cones close to the fovea. In 2002 Drexler et al., and in 2003 Miller et al., combined AO with optical coherence tomography (OCT) to provide higher axial resolution. Many modified systems have since been developed combining different technologies such as OCT and SLO together along with AO to obtain high resolution images. Another application for AO systems is its use in correcting optical aberrations in human eye and hence delivers high resolution images on the retina. AO systems provide a way to compensate for the optical aberrations in real time helping us to understand the impact of different optical aberrations on human vision. Understanding optical aberrations structure in human eye leads to innovation in areas such as retinal imaging, intra-ocular lens design. In this presentation, we will discuss AO systems and its applications in vision research.

Adaptive optics and its applications in vision research

Date: 2014-12-02
Speaker: Dr. Krishnakumar Venkateswaran
Venue: USO Seminar Hall

Abstract

A possible solution towards overcoming earth’s atmospheric turbulence aimed at providing high resolution astronomical images using ground based telescopes came through the advent of adaptive optics (AO). An AO system consists of a wave front sensor to measure the optical distortions in the wave front and an optical element to compensate the optical distortions. In 1953, Babcock proposed a method for compensating earth’s atmospheric turbulence but it was not until 1977 when Hardy and colleagues successfully demonstrated the use of AO in astronomy. Initially used for military purpose, AO made inroads in astronomy and is now being used almost as a staple part of any high resolution optical imaging system in astronomical telescopes.

Formation of current sheets through viscous relaxation

Date: 2014-09-12
Speaker: Sanjay Kumar
Venue: USO Seminar Hall

Abstract

From Parker’s magnetostatic theorem, formation of tangential discontinuities in magnetic field, or current sheets (CSs), are unavoidable in an equilibrium magnetofluid with infinite electrical conductivity and complex magnetic topology. These CSs are due to a failure of a magnetic field achieving forcebalance everywhere and preserving its topology while remaining in a spatially continuous state. The magnetic flux surfaces (MFSs) being the possible sites on which CSs develop, describing the magnetofluid evolution in terms of MFSs instead of vector magnetic field provides a direct visualization of the CS formation, helpful in understanding the governing dynamics. In this talk, I will discuss the magneto hydrodynamics simulations in which CS formation is demonstrated by employing an approach that utilizes MFSs. The simulations confirm development of CSs through a favourable contortion of MFSs, as the magneto fluid undergoes a topology-preserving viscous relaxation from an initial non-equilibrium state with twisted magnetic field. A crucial finding of this work is in its demonstration of CS formation at spatial locations away from the magnetic nulls.

Informal discussion on current Sheet formation

Date: 2014-09-01
Speaker: Dr.Ramitendranath Bhattacharyya
Venue: USO Seminar Hall

Abstract

Formation of magnetic discontinuities in a magnetofluid with large electrical conductivity

Date: 2014-08-22
Speaker: Dinesh Kumar
Venue: USO Seminar Hall

Abstract

The high Lundquist number S (\approx 10^{12}) of the solar corona renders coronal magnetofluid to be near-ideal in a sense that the condition of flux-freezing holds to a good approximation. Under this condition of flux-freezing the coronal magnetofluid can be partitioned into contiguous subvolumes of fluid each of which entraps its own magnetic flux. If two such subvolumes press into each other and come into direct contact by squeezing out a third interstitial subvolume, then under favorable conditions the magnetic field is expected to get discontinuous at the common surface of interaction and a current sheet is formed there. In a near-ideal system the current sheets decay through magnetic reconnection as a minimum threshold in local S is achieved where the otherwise negligible Ohmic dissipation becomes important. The above process of CS formation and its subsequent decay is responsible for a multitude of eruptive phenomena observed in the solar corona and provides a possible explanation for the corona to be at million degree Kelvin temperature. In this talk, I will present numerical demonstration of the formation of magnetic discontinuities based on suitable Initial Value Problems (IVPs) relevant to coronal physics.

Multi-wavelength Investigations of Solar Eruptive Phenomena

Date: 2014-08-19
Speaker: Upendra Kushwaha
Venue: USO Seminar Hall

Abstract

Solar flares are characterized by the sudden release of excess energy stored in the magnetic fields of solar corona. The modern multi-wavelength observations have immensely improved our understanding of the various physical processes occurring in different atmospheric layers of the Sun during a solar flare. The standard flare model has been successful in broadly recognizing these physical processes as the consequence of large-scale magnetic reconnection in the corona. In this talk, I will present multi-wavelength studies of a few intriguing solar flares and associated eruptive phenomena. For these investigations, we have analyzed contemporary data sets at superior temporal, spatial and spectral domains from various space -based observatories including RHESSI, SDO, TRACE, and NoRH. I will highlight important results of these studies which aim to provide crucial evidences to understand pre-flare conditions, triggering mechanism, and energy release processes.

Space Weather Phenomena during the Modern Era

Date: 2014-08-11
Speaker: Bruce T. Tsurutani,
Venue: USO Seminar Hall

Abstract

I will discuss some new aspects of space weather developed over the last few years. The causes of low geomagnetic activity during the recent solar minimum (2009, not 2008) will be explained. Geomagnetic activity during the CAWSES II interval of 5-17 March 2012 (rising phase of the solar cycle) will be discussed in some detail. HILDCAAs and interplanetary Alfven wave effects (during solar cycle declining phases) will be reviewed. This will be presented to serve as background to new results on the effects of HILDCAAs/High Speed Streams on relativistic electron acceleration, ionospheric TEC enhancements and NOx enhanced radiation. Finally I will discuss the effects of a ?perfect? ICME might have on the Earth and its environment.

Space weather phenomena during the modern era

Date: 2014-08-11
Speaker: Prof. Bruce T. Tsurutani
Venue: USO Seminar Hall

Abstract

I will discuss some new aspects of space weather developed over the last few years. The causes of low geomagnetic activity during the recent solar minimum (2009, not 2008) will be explained. Geomagnetic activity during the CAWSES II interval of 5-17 March 2012 (rising phase of the solar cycle) will be discussed in some detail. HILDCAAs and interplanetary Alfven wave effects (during solar cycle declining phases) will be reviewed. This will be presented to serve as background to new results on the effects of HILDCAAs/High Speed Streams on relativistic electron acceleration, ionospheric TEC enhancements and NOx enhanced radiation. Finally I will discuss the effects of a “perfect” ICME might have on the Earth and its environment

Discussion on symmetry followed by interaction session

Date: 2014-07-18
Speaker: Prof. Ashok Das
Venue: USO Seminar Hall

Abstract

Stokes profile inversion technique

Date: 2014-06-30
Speaker: Rahul Yadav
Venue: USO Seminar Hall

Abstract

Inversion techniques are the most powerful and sophisticated tool to infer the information about the solar magnetic field and the thermodynamic properties from the spectral line and Stokes profiles.They are based on non-linear fitting of the synthesized stokes profiles with the observed ones, generally using the Levenberg-Marquardt algorithm. We are developing an inversion code to solve the polarized radiative transfer equations. The code assumes that the properties of solar atmosphere are well described by the Milne-Eddington atmosphere. In this talk, I will share my understanding about the implementation of inversion techniques and specifically discuss the synthesis of Stokes profiles.

Kinematic evolution of CMEs in the heliosphere

Date: 2014-06-02
Speaker: Wageesh Mishra
Venue: USO Seminar Hall

Abstract

Coronal Mass Ejections (CMEs) are the potential drivers of many space weather events and the estimation of their arrival time near 1 AU is a crucial problem for a solar-terrestrial physicist. Since the discovery of CMEs, several methods have been developed to estimate their arrival time, mainly using the coronagraphic observations near the sun or using empirical, statistical or numerical MHD models. Before the era of heliospheric imagers, studies were limited to use of only two point observations of CMEs, one near the Sun as remote sensing observations and other near the Earth viz. in situ observations. Such studies are not sufficient for accurate arrival time prediction of CMEs. In this talk, I will first revisit the physics of appearance of a CME and some inherent difficulties in reliably estimating its kinematics and arrival time.Then, I will show how continuous tracking of CMEs from near the Sun to the Earth and beyond, is possible using J-maps constructed from SECCHI/STEREO images. I will show, in order to understand the propagation of CMEs, we have estimated their kinematics by implementing the geometric triangulation technique. The estimated kinematics is used as input to the drag based model of CME propagation for the distance where CMEs could not be tracked unambiguously. This approach improves the estimation of the arrival time as well as the transit velocity of a CME at 1 AU. In the end, I will emphasize that use of kinematics (even deprojected, i.e. 3D) of CMEs, estimated in coronagraphic field-of-view is often not sufficient for accurately predicting their arrival time near the Earth.

2013

Declining solar magnetic fields: Are we heading towards a Maunder minimum?

Date: 2013-10-25
Speaker: Prof. S. Ananthakrishnan
Venue: USO Seminar Hall

Abstract

One of the primary indicators of Solar activity is the Sunspot number and the associated 11 year solar cycle. This activity is controlled by the solar magnetic field. There are clear indications based on a variety of studies that the agnetic field on the Sun has been steadily decreasing in the past ~ 20 years resulting in lower activity on the Sun. The Sunspot formation has decreased by ~ 30% since the early 90’s. It has been speculated that if this continues, there will be no sunspots by the latter part of this decade, leading to a Maunder-like minimum in the next cycle. Using Interplanetary scintillation data from radio telescopes, surface photospheric fields measured by National Solar Observatory and He abundances measured by ACE, SDO spacecraft, my collaborators from PRL, Ahmedabad & Harvard Smithsonian Observatory and I have been studying this monotonic decrease. Interplanetary Scintillation observations between 1983 and 2009 clearly show steady drop in the turbulence levels in the entire inner heliosphere starting from around 1995. Our recent analysis of the solar magnetic fields have shown that a steady decline of the fields have taken place since around 1996 and meridional flows also appear to have changed. Similarly, Helium abundance dropped dramatically during 2008-2010. All these lead us to state that the build-up to the deepest solar minimum in 100 years actually began more than a decade earlier. We will examine the evidence in detail in this talk.

Oceanic nitrogen cycling: new results based on isotopic tracers

Date: 2013-09-27
Speaker: Prof. R. Ramesh
Venue: USO Seminar Hall

Abstract

Nitrogen is abundant in the Earth’s atmosphere, but much of it is not directly useful for life. Reactive nitrogen is needed for life processes and a small amount of reactive nitrogen is controlling life processes and hence the global carbon cycle. Over the last decade, we have investigated various aspects on the marine nitrogen cycle in the Indian Ocean. Using 15N and 13C tracers we have quantified, besides the biological productivity in the ocean (rate at which carbon is fixed by photosynthesis by marine planktons, measured in units of g C m–2day–1) and its temporal and spatial variability, the ‘new production’, the fraction of the carbon that is dispatched to the deep ocean to stay for longer time scales. We have developed experimental methodologies to measure the direct fixation of atmospheric nitrogen by marine diazatrophs such as Trichodesmium in the water column and also sediments. Further we have quantified the nitrification process, which compensates for the loss of reactive nitrogen to the atmosphere by denitrification. For the latter, we have modified the traditional Rayleigh isotopic fractionation model. We have also evaluated the nitrogen transport to the ocean through rivers and atmospheric transport. In this talk, while highlighting some important new results, we also propose to discuss current and future research in this area.

Magnetohydrodynamic relaxation of visco-resistive plasma

Date: 2013-07-12
Speaker: Sanjay Kumar
Venue: USO Seminar Hall

Abstract

The relaxation dynamics of a magnetized plasma system is a subject of fundamental importance in magnetohdrodyamics. The terminal states of such dynamical process are found to be rather quiescent and long lived, called as relaxed state. For example, in laboratory plasma confinement scheme like spheromak and RFP, magnetic field is believed to be in relax state. In solar corona, more than expected life time of coronal loops qualify them as relaxed states. The traits are to be looked for in a relaxing system are, predominantly non linearity and ideal integrals of motion which are conserved in absence of dissipation. In most of the existing theories of relaxation, only the terminal states are predicted without any details of the dynamics. In our study, we have tried to explore the dynamics of relaxation in a visco-resistive plasma with coronal magnetic field configuration as a prototype example using numerical simulation.

Fast solar polarimeter: Concept and the lab measurements

Date: 2013-05-15
Speaker: Dr K. Nagaraju
Venue: USO Seminar Hall

Abstract

A new polarimeter is under development at the MPS towards a goal of carrying out high precision spectropolarimetric observations on the Sun, combined with increased high spatial resolution. The polarimeter is based on pnCCD detector technology from PNSensor. The CCD detector can be operated at frame rates of up to 1000 frames/s to suppress spurious polarization signals induced by the atmospheric turbulence or instrument jitter. The polarization modulator is based on two ferro-electric liquid crystals and two static retarders. Achromatism in terms of polarimetric efficiency is achieved through appropriate positioning of the retarders. In this talk I will discuss about working principle and laboratory test results of the new polarimeter.

Narrow band imager for Multi Application Solar Telescope at Udaipur Solar Observatory

Date: 2013-04-26
Speaker: A Raja Bayanna
Venue: USO Seminar Hall

Abstract

Multi-Application Solar Telescope (MAST) is an off-axis Gregorian solar telescope of 50 cm clear aperture being installed at the lake site of Udaipur Solar Observatory (USO). A narrow band imager is being developed for near simultaneous observations of the solar atmosphere at different heights. The heart of the system is two LiNbO3 Fabry-Perot (FP) etalons working in tandem. It is important to calibrate the system for a change in voltage and a change in temperature for near simultaneous observations in different wavelengths. A Littrow spectrograph was set up to calibrate the FP etalons using a 15 cm refractor as a light feed. Calibration is carried out for the solar spectral lines at Fe I 6173 Å, and Ca K 8542 Å. In this presentation we discuss the temperature and voltage tuning of the system. We also present the details of the calibration set-up and obtained parameters along with the first-light results of the system.

Characterization of LCVRs for MAST polarimeter

Date: 2013-04-25
Speaker: Alok Ranjan Tiwary
Venue: USO Seminar Hall

Abstract

Spectro-polarimetry analyzes light as a function of its two most important characteristics: wavelength and state of polarization and is a powerful tool for measuring the magnetic field on the Sun. The observational aim of solar spectro-polarimetry is to record the Stokes vector as accurately as possible with highest spectral, spatial and temporal resolution. A Polarimeter is being developed at USO for measuring the vector magnetic field in the solar atmosphere at two different heights, and it will be used with the newly installed MAST. We plan to use two LCVRs and a linear polarizer for the MAST Polarimeter. LCVRs are electro-optically tunable retarders. Characterization of each LCVR is important in order to get the accurate retardance and voltage dependence for a particular wavelength. In this presentation, we discuss about the calibration of the LCVRs for two solar spectral lines at Fe I 6173 Å, and Ca K 8542 Å. We also present the details of the calibration set-up and the obtained results.

Determination of Mueller matrix of an optical element with Simon-Mukunda polarization gadget

Date: 2013-02-18
Speaker: Salla Gangi Reddy
Venue: USO Seminar Hall

Abstract

To characterize the polarization changes due to any optical element, one needs to determine the Mueller matrix of that element. From the information obtained by Mueller matrix, one can know the performance of an optical system and how to compensate those changes by using wave plates. In this talk, I will discuss a novel method to determine the Mueller matrix and the error associated with it due to the optical system used for its determination.

Report on visit to NCU, Taiwan to attend ISWWS-2013

Date: 2013-02-11
Speaker: Wageesh Mishra
Venue: USO Seminar Hall

Abstract

In this talk, I will present a very brief overview of scientific lectures delivered by various experts in International Space Weather Winter School, held during 21- 26th January 2013. I will discuss about various hands-on projects allotted to participants of winter school. Mainly, I will discuss the theory of Interplanetary scintillation and its importance to understand the density fluctuations in the heliosphere. I will also show few results on evolution of Coronal Mass Ejections in the interplanetary medium obtained by implementing IPS technique, various MHD models and using Solar Mass Ejection Imager (SMEI) observations.

Hunting for Blackholes with LIGO- India

Date: 2013-02-05
Speaker: Prof. Fred Raab Head
Venue: USO Seminar Hall

Abstract

Theoretical study of the solar magnetic cycle and its irregularities

Date: 2013-02-04
Speaker: Dr. Bidya Binay Karak
Venue: USO Seminar Hall

Abstract

The solar cycle is not regular. The strength as well as the period varies from cycle to cycle. One puzzling aspect of this sunspot cycle is the Maunder minimum in 17th century when sunspots disappeared for about 70 years. Indirect studies suggest that there were several other such events in the past. The motivation of my talk will be first to understand the generation and the evolution of the large-scale magnetic field of the Sun and then to model some irregular features of the solar cycle. I shall discuss a flux transport dynamo model to study the evolution of magnetic fields in the Sun. In this model, the toroidal field is generated by the strong differential rotation near the base of the convection zone and the poloidal field is generated near the solar surface from the decay of sunspots. The turbulent diffusion, the meridional circulation and the turbulent pumping are the important flux transport agents in this model which communicate these two spatially segregated source regions of the magnetic field. With this dynamo model, I shall explain several aspects of the solar cycle including grand minima. I shall also discuss the predictability of the future solar cycle using dynamo models