arXiv subjects

Bhola N. Dwivedi

Publications and source records attributed to Bhola N. Dwivedi.

14 recordsLinked to original sources

arXiv2026

Sigmoid Formation, Filament Destabilization, and Initiation of Weak Flare by Tether-Cutting Reconnection

We have studied a B-class solar flare and an associated filament eruption through multi-wavelength observations. The flare triggers at 16:24~UT on June 7$^{th}$, 2017 from an active region (AR) 12661, and it maximizes at 16:54~UT. The magnetic flux cancellation occurs near the polarity inversion line (PIL) preceding the flare, and ultraviolet (UV) brightenings occur in the pre-flare phase at the flux cancellation sites, suggesting the reconnection occurs in the lower atmosphere, initially. The S-shaped sigmoid forms through successive steps in corona, i.e., small-scale brightenings, helical/twisted field lines, bright patches, and finally, a developed sigmoid. It justifies that runaway reconnection within the coronal arcades forms the sigmoid within the filament. The differential emission-measure (DEM) analysis reveals the existence of the plasma at a temperature of more than 10 MK within the sigmoid. The initial magnetic reconnection reorganizes the field overlying the filament as per the tether-cutting model. Therefore, it enables the filament to rise slowly, and around~16:41~UT, the eruption phase of the filament begins. The filament eruption removes the overlying coronal field, including the sigmoid. During the eruption phase, we have found intersecting/crossing of coronal loops and jet-like structures far away from the sigmoid-filament system. In conclusion, all the observational findings (e.g., magnetic flux convergence, cancellation, UV brightenings, and spatial and temporal correlation between formation/evolution of the sigmoid and rise/eruption of the filament) suggest that the formation of a solar flare and the eruption of the filament are consistent with the tether-cutting model of solar eruption.

astro-ph.SR↗

arXiv2025

Questions related to the Deflection of Light by Gravity determined by Soldner, Einstein and Schwarzschild

Before we discuss the deflection of light in a gravitational field, we give a brief overview of some basic physical formulas on photon properties, generation and propagation. The much debated problems of the redshift and the photon propagation in a gravitational field is then considered and applied to the calculation of the speed of light. Many citations are given in direct quotations to avoid any misunderstandings. If the quotations are in German, an English translation is provided. Based on this speed, calculated and measured results are recalled on the deflection of light, with emphasis on the deflection near the Sun. We conclude that the speed of light and the deflection angle can be determined by energy and momentum conservation principles.

physics.hist-ph↗

arXiv2025

Doppler, gravitational and cosmological redshifts

Ortiz and Ibarra-Castor (2024) have presented a "Generalized redshift formula" taking account of only energy conservation considerations. Contrary to their claim, we emphasize to invoke both energy and momentum considerations in order to deduce all three types of redshift (Doppler, gravitational and cosmological). We formulate our views on the three physical e ects in a consistent manner in addition to addressing the lack of relevant references in Ref. (Ortiz and Ibarra-Castor, 2024)

physics.gen-ph↗

arXiv2020

On the radial acceleration of disk galaxies

The physical processes defining the dynamics of disk galaxies are still poorly understood. Hundreds of articles have appeared in the literature over the last decades without arriving at an understanding within a consistent gravitational theory. Dark matter (DM) scenarios or a modification of Newtonian dynamics (MOND) are employed to model the non-Keplerian rotation curves in most of the studies, but the nature of DM and its interaction with baryonic matter remains an open question and MOND formulates a mathematical concept without a physical process. We have continued our attempts to use the impact theory of gravitation for a description of the peculiar acceleration and velocity curves and have considered five more galaxies. Using published data of the galaxies NGC 3198, NGC 2403, NGC 1090, UGC 3205 and NGC 1705, it has been possible to find good fits without DM for the observed disk velocities and, as example, also for the extraplanar matter of NGC 3198.

astro-ph.GA↗

arXiv2020

CME Productive and Non-productive Recurring Jets Near an Active Region AR11176

We study the recurring jets near AR11176 during the period 2011 March 31 17:00 UT to April 1 05:00 UT using observations from the Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO). Mini-filaments (mini-filament1 & 2) are found at the base of these recurring jets where mini-filament1 shows the partial signature of eruption in case of Jet1-3. However, the mini-filament2 shows a complete eruption driving a full blow-out jet (Jet4). The eruption of mini-filament2 triggers C-class flare and Jet4 eruption. The eruption of Jet4 triggers a coronal mass ejection (CME). The plane-of-sky velocity of recurring jets (Jet1-4) results in 160 km/s, 106 km/s, 151 km/s and 369 km/s. The estimated velocity of CME is 636 km/s. The continuous magnetic flux cancellation is observed at the base of the jet productive region which could be the cause of the eruption of mini-filaments and recurring jets. In the former case, the mini-filament1 shows partial eruption and first three jets (Jet1-3) are produced, but the rate of cancellation was rather low. However, in the latter case, mini-filament2 fully erupts (perhaps because of a higher cancellation rate), and this triggers a C-class flare and a CME-productive jet. At the base of first three jets (Jet1-3), the mini-filament1 causes to push the overlying dynamic complex thin loops resulting in the reconnection and drives the jet (Jet1-3) eruptions. The formation of the plasma blobs are observed during the eruption of the first jet (Jet1).

astro-ph.SR↗

arXiv2019

Signatures of red-shifted footpoints in the quiescent coronal loop system

We observed quiescent coronal loops using multi-wavelength observations from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) on 2016 April 13. The flows at the footpoints of such loop systems are studied using spectral data from Interface Region Imaging Spectrograph (IRIS). The Doppler velocity distributions at the footpoints lying in the moss region show the negligible or small flows at Ni I, Mg II k3 and C II line corresponding to upper photospheric and chromospheric emissions. Significant red-shifts (downflows) ranging from (1 to 7) km/s are observed at Si IV (1393.78 A; log(T/K) = 4.8) which is found to be consistent with the existing results regarding dynamical loop systems and moss regions. Such downflows agree well with the impulsive heating mechanism reported earlier.

astro-ph.SR↗

arXiv2019

Twin CME Launched by a Blowout Jet Originated from the Eruption of a Quiet-Sun Mini-filament

We study a quiet-Sun blowout jet which is observed on 2014 May 16 by the instruments on board Solar Dynamics Observatory (SDO). We find the twin CME as jet-like and bubble-like CME simultaneously as observed by LASCO C2 on board Solar and Heliospheric Observatory (SoHO), Solar Terrestrial Relation Observatory (STEREO A and STEREO B/COR2). They are respectively associated with the eruption of the northern and southern sections of the filament. A circular filament is rooted at the internetwork region at the base of the blowout jet. The collective magnetic cancellation is observed by SDO/HMI line of sight (LOS) magnetograms at the northern end of the filament, which makes this filament unstable and further makes it to erupt in two different stages. In the first stage, northern section of the filament is ejected, and causes an evolution of the northern part of the blowout jet. This part of the blowout jet is further extended as a collimated plasma beam to form a jet-like CME. We also observe the plasma blobs at the northern edge of the blowout jet resulting from Kelvin-Helmholtz (K-H) instability in its twisted magneto-plasma spire. In the second stage, southern section of the filament erupts in form of deformed/twisted magnetic flux rope which forms the southern part of the blowout jet. This eruption is most likely caused by the eruption of the northern section of filament, which removes the confined magnetic field of the southern section of the filament. Alternative scenarios may be a magnetic implosion between these magnetic structures confined in a much larger magnetic domain. This eruption of southern section of the filament further results in the bubble-like CME in the outer corona.

astro-ph.SR↗

arXiv2019

Plasma flows in the cool loop systems

We study the dynamics of low-lying cool loop systems for three datasets as observed by the Interface Region Imaging Spectrograph (IRIS). Radiances, Doppler shifts and line widths are investigated in and around observed cool loop systems using various spectral lines formed between the photosphere and transition region (TR). Footpoints of the loop threads are either dominated by blueshifts or redshifts. The co-spatial variation of velocity above the blue-shifted footpoints of various loop threads shows a transition from very small upflow velocities ranging from (-1 to +1) km/s in the Mg\,{\sc ii} k line (2796.20~Å; formation temperature: log (T/K) = 4.0) to the high upflow velocities from (-10 to -20) km/s in Si\,{\sc iv}. Thus, the transition of the plasma flows from red-shift (downflows) to the blue-shift (upflows) is observed above the footpoints of these loop systems in the spectral line C\,{\sc ii} (1334.53~Å; \log (T/K) = 4.3) lying between Mg\,{\sc ii} k and Si\,{\sc iv} (1402.77~Å; log (T / K) = 4.8). This flow inversion is consistently observed in all three sets of the observational data. The other footpoint of loop system always remains red-shifted indicating downflowing plasma. The multi-spectral line analysis in the present paper provides a detailed scenario of the plasma flows inversions in cool loop systems leading to the mass transport and their formation. The impulsive energy release due to small-scale reconnection above loop footpoint seems to be the most likely cause for sudden initiation of the plasma flows evident at TR temperatures.

astro-ph.SR↗

arXiv2018

Michelson-Morley experiment, Doppler effect, aberration of light and the aether concept

After an overview of various citations relevant in the context of photon propagation, the relativistic Doppler effect and the addition theorem of velocities are first derived taking into account momentum and energy conservation. Clocks and the aberration of light are treated next, before the lengths of rods and the Lorentz transformations are discussed. The Michelson-Morley experiment is described at rest and in motion with respect to a preferred aether system, first under the assumption of an operation in vacuum. It is concluded that the aether concept is fully consistent with the formal application of the Special Theory of Relativity (STR). Whether a determination of the speed of the laboratory system relative to the aether is possible, is considered next either for an operation of the experiment in vacuum or in a medium with an index of refraction not equal to one. In both cases, the answer appears to be negative.

physics.gen-ph↗

arXiv2017

Two-fluid numerical simulations of solar spicules

We aim to study the formation and evolution of solar spicules by means of numerical simulations of the solar atmosphere. With the use of newly developed JOANNA code, we numerically solve two-fluid (for ions + electrons and neutrals) equations in 2D Cartesian geometry. We follow the evolution of a spicule triggered by the time-dependent signal in ion and neutral components of gas pressure launched in the upper chromosphere. We use the potential magnetic field, which evolves self-consistently, but mainly plays a passive role in the dynamics. Our numerical results reveal that the signal is steepened into a shock that propagates upward into the corona. The chromospheric cold and dense plasma lags behind this shock and rises into the corona with a mean speed of 20-25 km s$^{-1}$. The formed spicule exhibits the upflow/downfall of plasma during its total lifetime of around 3-4 minutes, and it follows the typical characteristics of a classical spicule, which is modeled by magnetohydrodynamics. The simulated spicule consists of a dense and cold core that is dominated by neutrals. The general dynamics of ion and neutral spicules are very similar to each other. Minor differences in those dynamics result in different widths of both spicules with increasing rarefaction of the ion spicule in time.

astro-ph.SR↗

arXiv2016

Magnetostatics and the electric impact model

The action of certain static magnetic fields on charged test particles is interpreted as a consequence of the interaction of the particles with electric dipole distributions emitted by other charged particles in relative motion. The dipole model of electric forces was initially conceived to emulate Coulomb's law, but is applied here to a wide class of phenomena, such as forces between parallel conductors, a relativistic correction of Biot--Savart's law, and the magnetic moment of a current loop.

physics.gen-ph↗

arXiv2014

On the gravitational redshift

The study of the gravitational redshift\,---\,a relative wavelength increase of $\approx 2 \times 10^{-6}$ was predicted for solar radiation by Einstein in 1908\,---\,is still an important subject in modern physics. In a dispute whether or not atom interferometry experiments can be employed for gravitational redshift measurements, two research teams have recently disagreed on the physical cause of the shift. Regardless of any discussion on the interferometer aspect\,---\,we find that both groups of authors miss the important point that the ratio of gravitational to the electrostatic forces is generally very small. For instance, the gravitational force acting on an electron in a hydrogen atom situated in the Sun's photosphere to the electrostatic force between the proton and the electron is approximately $3 \times 10^{-21}$. A comparison of this ratio with the predicted and observed solar redshift indicates a discrepancy of many orders of magnitude. Here we show, with Einstein's early assumption of the frequency of spectral lines depending only on the generating ion itself as starting point, that a solution can be formulated based on a two-step process in analogy with Fermi's treatment of the Doppler effect. It provides a sequence of physical processes in line with the conservation of energy and momentum resulting in the observed shift and does not employ a geometric description. The gravitational field affects the release of the photon and not the atomic transition. The control parameter is the speed of light. The atomic emission is then contrasted with the gravitational redshift of matter-antimatter annihilation events.

physics.gen-ph↗

arXiv2013

Estimation of Plasma Properties and Magnetic Field in a Prominence-like Structure as Observed by SDO/AIA

We analyze a prominence-like cool plasma structure as observed by Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). We perform the Differential Emission Measure (DEM) analysis using various filters of AIA, and also deduce the temperature and density structure in and around the observed flux-tube. In addition to deducing plasma parameters, we also find an evidence of multiple harmonics of fast magnetoacoustic kink waves in the observed prominence-like magnetic structure. Making use of estimated plasma parameters and observed wave parameters, under the baseline of MHD seismology, we deduce magnetic field in the flux-tube. The wave period ratio P1/P2 = 2.18 is also observed in the flux-tube, which carries the signature of magnetic field divergence where we estimate the tube expansion factor as 1.27. We discuss constraints in the estimation of plasma and magnetic field properties in such a structure in the current observational perspective, which may shed new light on the localized plasma dynamics and heating scenario in the solar atmosphere.

astro-ph.SR↗

arXiv2013

Photon in a cavity -- a Gedankenexperiment

The inertial and gravitational mass of electromagnetic radiation (i.e., a photon distribution) in a cavity with reflecting walls has been treated by many authors for over a century. After many contending discussions, a consensus has emerged that the mass of such a photon distribution is equal to its total energy divided by the square of the speed of light. Nevertheless, questions remain unsettled on the interaction of the photons with the walls of the box. In order to understand some of the details of this interaction, a simple case of a single photon with an energy $E_ν= h\,ν$ bouncing up and down in a static cavity with perfectly reflecting walls in a constant gravitational field $\vec{g}$, constant in space and time, is studied and its contribution to the weight of the box is determined as a temporal average.

physics.class-ph↗