The space weather inside the heliosphere is dictated by various dynamic processes of the sun; Among these, Coronal Mass Ejections (CMEs) stand out due to their significant impact on space weather. The Geo-effective Interplanetary Coronal Mass Ejections (ICMEs) can trigger severe space weather events, such as geomagnetic storms, which pose substantial risks to modern technological...
Astronomers have uncovered a captivating facet among the myriad celestial bodies, known as Variable Stars. These mysterious entities undergo changes in their radiance over time, offering astronomers a unique opportunity to study the complexities of stars. Since 1911, the American Association of Variable Star Observers (AAVSO) has been diligently monitoring these stars. Variable star...
Solar radio bursts are often byproducts of phenomena like coronal mass ejections (CMEs) and/or solar flares. They are capable of producing very high brightness temperatures and hence lead to a large increase in the observed intensity. Depending upon the details of the physical processes and emission mechanisms involved, their dynamic spectra can show markedly different spectro-temporal...
Magnetic field switchbacks, crucial for understanding solar wind dynamics, are typically identified through magnetic field reversals (Dudok de Wit et al., 2020). This methodology is susceptible to mistakes stemming from data contamination caused by phenomena such as coronal mass ejections (CMEs), flux ropes, magnetic clouds (MICCS), heliospheric current sheets (HCS), partial heliospheric...
Coronal mass ejections (CMEs), originating from the sun's corona, are large-scale eruptions of plasma and magnetic flux that propagate into interplanetary space, and are capable of significantly influencing the dynamic environment of the inner solar system. Previous studies have established that CMEs exhibit turbulent behavior, characterized by energy cascades from larger to smaller scales...
We investigate the handedness in the solar magnetic structures like chromospheric filaments and photospheric active regions using observations obtained from GONG, KSO, and SDO/HMI. At its initial stage near the east limb, we identified a right-bearing sense for the filament barbs and negative helicity in the supporting active region (AR). Subsequently, we observed an emergence of positive...
Abstract
We have analysed the geoeffectiveness of halo coronal mass ejections (HCMEs) by investigating a total of 56 events observed between December 2019 and December 2023, during the rising phase of Solar Cycle 25. During this period, we considered only halo CMEs associated with flares, frontside halo CMEs, and excluding the poor events. Halo coronal mass ejections are generally faster...
The solar corona and solar wind are often observed to have elemental abundances different from the solar photosphere, and the observed fractionation appear to depend on the element's first ionization potential, and it is thought to be linked to the processes leading to the solar atmospheric heating. We have used coordinated coronal (Hinode/EIS) and chromospheric and transition region (IRIS)...
For my MSc thesis, I focused on investigating the timescales of interactions between Earth's magnetosphere and solar transients, with an emphasis on Coronal mass ejections (CMEs) as they traveled through space and passed Earth. CMEs, which are massive expulsions of plasma and magnetic fields from the Sun, can have significant effects on Earth's magnetic environment. My goal was to better...
Helioseismology can detect active regions on the Sun’s far side days before they rotate onto the Earth’s side, using solar acoustic oscillations. These far-side maps provide an important input for space weather models. Recent advances in theoretical and computational helioseismology have improved far-side imaging, which enables high-confidence detection and daily tracking of medium-size active...
Coronal mass ejections (CMEs) are intense solar phenomena where plasma and magnetic fields are ejected from the Sun, playing a significant role in influencing Space Weather. However, traditional coronagraphs struggle to accurately capture the early stages of Earth-directed CMEs due to projection-related distortions. Coronal dimmings, which manifest as localized reductions in...
Solar jets are described as collimated, beam-like structures that eject plasma along straight or slightly oblique magnetic field lines. They can be observed from the lower solar atmosphere up to the corona, spanning a wide range of temperatures. In this study, we present an analysis of recurrent solar jets observed on 6 March 2022 near the active region NOAA 12960, using data from the...
During the solar flares, whole solar atmosphere gets heated; however, the energy deposition process in the lower solar atmosphere is still unclear. In this paper, we present spectroscopic and imaging observations of a small-scale transient of life-time $\approx$2-min and subsequent formation of a hot transient loop of life-time $\approx$4-min in a solar active region. The event is classified...
The dynamic connection between the solar corona and the heliosphere is critical for understanding and forecasting space weather. Active regions and solar eruptions, including extreme events, significantly influence the heliospheric environment, with profound implications for Earth's magnetosphere. Leveraging data from new space missions like ASPEX-SWIS from Aditya-L1, Parker Solar Probe (PSP),...
Three-dimensional (3D) magnetic nulls are abundant in the solar atmosphere, as have been firmly established through contemporary observations [1]. They are established to be important magnetic structures in solar atmosphere, for example, jets [2] and circular ribbon flares [3,4,5]. The flare emissions at the footpoints of the fan field lines constitute a closed circular flare ribbon. Recent...
In a stellar atmosphere, the resonance line polarization arises from scattering of limb-darkened radiation field by atoms. This spectral line polarization is severely affected particularly in the wings, when the line photons suffer scattering on electrons in thermal motion. Electron scattering opacity is known to be significant in higher layers of sun and stars, especially the hotter stars....
The operational solar wind prediction models used by the community are based on the Potential Field Source Surface (PFSS) model for the magnetic field using synoptic magnetograms. Previous studies comparing observed and modeled open magnetic flux at L1 based on PFSS extrapolations have suggested the need to optimize the source
surface (SS) height with the phase of the solar cycle. The current...
Coronal mass ejections (CMEs) that cause geomagnetic disturbances on the Earth can be found in conjunction with flares, filament eruptions, or independently. Though flares and CMEs are understood as triggered by the common physical process of magnetic reconnection, the degree of association is challenging to predict. From the vector magnetic field data captured by the Helioseismic and Magnetic...
Large-scale coronal structures, such as helmet streamers (HS) and pseudo-streamers (PS), have been studied extensively as potential source regions for solar wind generation. Historically, white-light observations of the outer corona have provided insights into these features. Yet, the dynamics of HS and PS are more clearly observed in the middle corona, where the Sun’s magnetic field...
Solar flares are transient events occurring over a time scale of minutes to hours, characterized by a sudden release of magnetic energy in the form of heat and kinetic energy of the plasma. These events are believed to be the manifestations of the magnetic reconnection process. We have explored the effects of 3D reconnection in solar flares, focusing on (a) magnetofluid dynamics from the...
This study investigates the origins, characteristics, and impacts of Geo-effective Coronal Mass Ejections (CMEs) on Earth's space environment during Solar Cycle 24 th (2009-2019),with a focus on their contribution to space weather phenomena. Specifically, we examine Interplanetary Coronal Mass Ejections (ICMEs) detected at the first Lagrangian point (L1),using their key features such as...
The whole heliosphere is permeated by the solar wind. An important aspect of the solar wind is the suprathermal ion tail which is manifested in the form of particles in the energy range of a few keV/nucleon to several hundreds of keV/nucleon. In addition to the suprathermal ions, there are energetic ions having energy range exceeding 1 MeV/nucleon which are termed as solar energetic particles...
Magnetosonic waves and magnetic reconnection have been studied for a long time as two major processes responsible for coronal heating, solar wind acceleration, and other energetic eruptive processes in the Sun’s corona. Here, we study the mutual interactions between these two plasma processes in a physics-based numerical model. In this model, a velocity perturbation representing the effect of...
We investigate the temperature distribution for Alfvénic and non-Alfvénic regions in Interplanetary Coronal Mass Ejections (ICMEs). Our analysis reveals that approximately 63% of the ICME magnetic cloud regions are non-Alfvénic, while 37% exhibit Alfvénic characteristics, predominantly outward fluctuations. We observe significant temperature enhancements in Alfvénic regions, with the most...
We observe non-thermal radio emission with spectral indices ranging from 1 to 3, extending over megaparsec scales almost in the centre of the galaxy clusters containing largely collisionless plasma. To explain this, the electrons must be energized. While turbulence or shocks generated by merger events can accelerate electrons, their efficiency is relatively low.
We explore an alternative...
Heating in the solar atmosphere has been a long standing problem in solar physics. Despite advancements in both observational and theoretical frameworks, the precise mechanisms that heat the corona are not yet well understood. Phenomena like magnetic reconnection and wave heating have been suggested as the cause, but the extent to which each process contributes to the overall...
B.K.Tiwari
Department of Physics A.P.S.University Rewa (M.P)
Abstract
A study of the long-term modulation of galactic cosmic rays in positive and negative phases of the 22-year solar magnetic cycle, including a period of anomalously low solar activity between 2008 and 2020 is performed. Solar magnetic field lines reconnect with galactic ones in the negative phases. In the positive...
Solar energetic particle (SEP) events are one of the most crucial aspects of space weather that require continuous monitoring and forecasting using robust methods. We demonstrate a proof of concept of using a data-driven supervised classification framework on a multivariate time-series data set covering solar cycles 22, 23, and 24. We implement ensemble modeling that merges the results from...
Temporary perturbations in the Earth’s magnetosphere and upper atmosphere driven by coronal mass ejections (CME) are called geomagnetic storms. It is important to understand the solar sources of geomagnetic storms in order to constrain physical drivers of space weather. A severe geomagnetic storm was observed during 10-11 May 2024. It was the strongest storm on record in the last two decades...
Radial velocity measuring instruments are nearing the precision needed for detecting Earth-like exoplanets, yet a new challenge emerges the star's own fluctuations. Disentangling the signatures of spurious radial velocity changes because of photospheric fluid flows is a complicated, multidimensional problem. Traditional methods, though partly successful, haven't fully tapped into the...
Quasi-periodic oscillations (QPOs) observed in the solar chromosphere and transition region during flares offer valuable insights into the atmospheric response to sudden energy releases and the evolution of the magnetic field. We analyzed an M-6.5 class flare observed by the Interface Region Imaging Spectrograph (IRIS), emphasizing QPOs in the Doppler velocity measured in the Si IV line at the...
We present two case studies on solar energetic particle (SEP) events involving type III storms and type II bursts in metric and decmetric-hectometre (DH) wavelengths. In one case, a type III storm was disrupted by an eruption, while in the other, the storm remained unaffected. Both events featured fast and wide coronal mass ejections (CMEs) and regular type III bursts. Analysing Nancay...
When distant radio point sources are observed through the foreground solar corona or solar wind, they experience angular or scatter broadening, and lead to change in peak flux density, anisotropy, and orientation of the major axis of the source. Such modulations are useful for probing solar wind parameters such as the amplitude of turbulence, density modulation index, proton heating rates, and...
We investigate the reformation of a quiescent filament and its structural and physical properties over two Carrington rotations. Utilizing intensity and magnetic field observations from various ground-based and space-based observatories, we continuously tracked the filament's evolution throughout the observation period. Our analysis reveals that the filament reformed in the same region twice...
A Coronal Mass Ejection (CME) is a large-scale eruption of plasma and magnetic fields from the Sun into interplanetary space. In coronagraph observations, around one-third of CMEs exhibit a characteristic three-part structure consisting of a bright inner core, an outer leading edge, and a darker cavity in the middle. However, observations of the inner corona suggest this three-part structure...
Temporal and spatial variations in solar rotation with accurate determination and its correlation with solar activities are interesting topic in solar physics since earlier. Solar rotation can be measured by tracking the tracers across the solar disk, or via spectroscopy, or via flux modulation method using radio waves, X-rays, and UV rays that emitted out in the space. Solar Dynamics...
Exploration of solar radio dynamic spectrum provides us with an opportunity to probe the multi-scale energetic phenomena during coronal transients including large-scale eruptions. To monitor solar radio bursts at metric wavelengths, the Udaipur Solar Observatory, Physical Research Laboratory (USO-PRL) operates a low-cost solar radio observation facility based on CALLISTO spectrometers. In this...
Solar wind interaction with the planetary magnetic field (or a conducting ionosphere), results in the formation of a magnetosphere which may be intrinsic or induced, depending upon whether the planet has its own magnetic field or not. Plasma waves are the means through which different subsystems of the magnetosphere like the magnetopause, ionopause, plasmasphere, etc. interact with each other,...
Coronal dimmings on the Sun are transient reductions in coronal plasma emissions, often associated with Coronal Mass Ejections (CMEs) triggered by solar flares or filament eruptions. These dimmings typically last between 3 to 12 hours, characterized by a rapid decrease in intensity followed by a gradual recovery. In this study, we conduct a differential emission measure (DEM) analysis using a...
In May 2024, a series of solar eruptions occurred, triggered by a complex active region (β γδ ), leading to the extreme geomagnetic storm on May 10, 2024, the strongest storm in the last two decades. We investigate the kinematic and thermal evolution of coronal mass ejections (CMEs) responsible for this extreme event using multi-point coronagraphic data and near-Earth in-situ measurements,...
Scattering polarization in strong resonance lines such as the Ca I 4227 Å, formed in the chromosphere, can probe the chromospheric magnetic fields via the Hanle effect. Predominantly one-dimensional (1D) semi-empirical model atmospheres were used to study the linear polarization in this line. Recently, Harsh et al. (2024) studied the resonance scattering polarization in Ca I 4227 Å using...
