arXiv subjects

Sudip Mandal

Publications and source records attributed to Sudip Mandal.

At least 19 recordsLinked to original sources

arXiv2026

Improved reconstruction of the century-long solar magnetic field by incorporating morphological asymmetry in sunspots

Accurately modeling the solar magnetic field is important for understanding long-term solar activity and space weather, but it is challenging due to limited observations, especially near the poles. The Surface Flux Transport (SFT) model simulates how magnetic flux moves across the solar surface and contributes to the polar field, but it parametrizes emerged sunspots as simple symmetric bipolar regions and needs improvement by including more realistic sunspot features. In this study, we reconstruct the century-long evolution of the solar magnetic field, including the polar regions, using an improved SFT model. We incorporate cycle-dependent morphological asymmetry between leading and following sunspots, along with observationally derived tilt angles and sunspot area data for a century (1913-2016), to better represent magnetic flux transport and investigate the impact of asymmetry on polar field development. To study morphological asymmetry, we consider two cases: first, a long-term asymmetry factor calculated from the ratio of leading and following sunspot areas spanning over a century; second, the temporal asymmetry factor observed during solar cycle 23 applied to every solar cycle. Our simulated magnetic flux transport with inclusion of morphological asymmetry for both cases gets improved compared to the no asymmetry case in terms of enhanced low and mid-latitude magnetic flux and matches closely with observations. The simulated polar fields with asymmetry also show a better agreement with polar field observations for most cycles, particularly in capturing the timing of the polar field reversals and the peak amplitude during solar minima, which has severe consequences in solar cycle prediction

astro-ph.SR↗

arXiv2026

Polarization of decayless kink oscillations in a 3D MHD coronal loop model

Decayless kink oscillations are frequently observed in solar coronal loops and are considered potential contributors to coronal heating. Despite the ubiquity of this wave phenomenon, its driving mechanism remains unclear. Studies to derive the polarization state of these oscillations, which would be a key to identifying the drivers, have been limited due to observational constraints. We analyze a 3D MHD simulation of coronal loops using the MURaM code. Synthetic extreme ultraviolet (EUV) emission maps, combined with velocity diagnostics, are used to identify and characterize transverse wave motions in the simulated loop structures. This is the first demonstration of decayless kink waves emerging self-consistently in a 3D MHD loop-in-a-box model. The simulation produces persistent, low-amplitude, decayless kink oscillations that closely match observed properties. These oscillations arise spontaneously, without any imposed periodic driver, and exhibit clear linear polarization with oscillation planes not aligned to the principal axes. The observed coherency of linear polarization with oscillation cycles favors a self-sustained or quasi-steady type wave driver over a stochastic or broadband source.

astro-ph.SR↗

arXiv2025

A self-consistent 3D MHD model producing a solar blowout jet

Context. Solar blowout jets are a distinct subclass of ubiquitous extreme-ultraviolet (EUV) and X-ray coronal jets. Aims. Most existing models of blowout jets prescribe an initial magnetic field configurations and apply ad-hoc changes in the photosphere to trigger the jets. In contrast, we aim for a self-consistent magneto-convective description of the jet initiation. Methods. We employ a 3D radiation magnetohydrodynamic (MHD) model of a solar coronal hole region using the MURaM code. The computational domain extends from the upper convection zone to the lower corona. We synthesize the emission in the extreme UV and X-rays for a direct comparison to observations and examine the evolution of the magnetic field structure of the event. Results. In the simulation a twisted flux tube forms self-consistently, emerges through the surface and interacts with the pre-existing open field. Initially the resulting jet is of the standard type with a narrow spire. The release of the twist into the open field causes a broadening of the jet spire turning the jet into a blowout type. At the same time this creates a fast heating front propagating at the local Alfvén speed. The properties of the modeled jet closely match observations of blowout jets: a slow (180 km/s) mass upflow and a fast (500 km/s) propagating front form, the latter being a signature of the heating front. Also the timing of the jet with respect to the flux emergence and subsequent cancellation matches observations. Conclusions. The near-surface magneto-convection self-consistently generates a twisted flux tube that emerges through the photosphere. The tube then interacts with the pre-existing magnetic field by means of interchange reconnection. This transfers the twist to the open field region and produces a blowout jet that matches the main characteristics of this type of jet found in observations.

astro-ph.SR↗

arXiv2025

Strain-Controlled Magnetic Phase Transitions through Anisotropic Exchange Interactions: A Combined DFT and Monte Carlo Study

Epitaxial strain provides a powerful, non-chemical route to tune the properties of functional materials by manipulating the coupling between spin, charge, and lattice degrees of freedom. Using density functional theory (DFT) calculations and $\rm BiFeO_3$ as a model system, we first demonstrate how epitaxial strain exactly leads to anisotropic magnetic interactions where the exchange coupling along the $c$-axis differs from that in the $ab$-plane. We show that subtle structural modifications, specifically the distortion from a cubic to a tetragonal lattice, drive a magnetic phase transition from a G-type to a C-type antiferromagnetic (AF) phase. The anisotropy in magnetic interactions, which becomes prominent in the lower symmetry tetragonal phase, provides a direct link between the structural distortion and the potential change in magnetic ordering. For a more comprehensive study, we next investigate the role of strain in driving magnetic phase transitions within a half-filled one-band Hubbard model in three dimensions. In this framework, strain is introduced through anisotropic hopping processes between nearest- and next-nearest-neighbor sites, inspired by the DFT calculations. Using a semiclassical Monte Carlo (s-MC) approach, we construct ground state phase diagrams in the nonperturbative regime, which show how uniaxial strain stabilizes distinct magnetic ground states: Compressive strain drives a transition from a G-type to a C-type AF insulator, whereas tensile strain suppresses the C-type AF order, favoring an A-type AF phase. Overall, our combined DFT and s-MC calculations highlight that strain is a powerful tuning parameter for controlling competing magnetic phases by governing exchange coupling mechanisms in correlated systems, offering valuable insights for the design of strain-controlled materials.

cond-mat.str-el↗

arXiv2025

Combine effect of site dilution and long-range interaction on magnetic and transport properties in the half-filled Hubbard model

We investigate the magnetotransport properties of a diluted half-filled one-band Hubbard model with second-nearest-neighbor hopping on a simple cubic lattice, aiming to explore the possibility of metallicity in diluted antiferromagnetic systems. Our semiclassical Monte Carlo calculations reveal an antiferromagnetic metallic regime in diluted correlated materials. This unexpected metallic regime naturally leads to a central question: how does the introduction of dilution into an antiferromagnetic material, especially with long-range magnetic interactions, induce metallicity -- a feature not commonly associated with antiferromagnets? To address this question, we demonstrate that when the on-site repulsive Hubbard interaction strength is set to zero on a percentage of the sites (site dilution), the insulating state weakens due to percolative conduction among the diluted sites at low temperatures. Remarkably, this occurs without any significant alteration to the underlying long-range antiferromagnetic ordering in the system, thereby providing a pathway to realize antiferromagnetic metals. In addition, we show how the sublattice-dependent hopping can be exploited to engineer spin-polarized half-metallic antiferromagnets. Overall, our numerical results collectively provide a basis for understanding the combined effect of site dilution and competing interactions, which will assist in the design of new antiferromagnetic metals for future spintronic applications.

cond-mat.str-el↗

arXiv2025

Methods for quantum interference in atomic ensemble

An experimental method for obtaining quantum interference signal in atomic ensemble using a bi-chromatic field is discussed. Here, the quantum interference signal is obtained by scanning the magnetic field rather than conventional method of changing the frequency separation between the light fields. We could simultaneously observe resonances due to population redistribution and quantum superposition between non-degenerate states, which otherwise involves fundamentally different approaches. The method is implemented to Rubidium atoms in buffer gas filled as well as anti-relaxation coated atomic cells. Apart from phenomenological interest, the modified experimental procedure is found to be convenient for in-situ calibration of three axis magnetic coils. The investigation will be useful for high as well as low vector magnetic field sensing.

quant-ph↗

arXiv2025

Anomalous cross-field motions of solar coronal loops

Here, we present several examples of unusual evolutionary patterns in solar coronal loops that resemble cross-field drift motions. These loops were simultaneously observed from two vantage points by two different spacecraft: the High-Resolution Imager (HRI$_{EUV}$) of the Extreme Ultraviolet Imager aboard the Solar Orbiter and the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory. Across all these events, a recurring pattern is observed: Initially, a thin, strand-like structure detaches and shifts several megameters (Mm) away from a main or parent loop. During this period, the parent loop remains intact in its original position. After a few minutes, the shifted strand reverses its direction and returns to the location of the parent loop. Key features of this `split-drift' type evolution are: (i) the presence of kink oscillations in the loops before and after the split events, (ii) a sudden split motion at about 30~km.s$^{-1}$, with additional slow drifts, either away from or back to the parent loops, at around 5~km.s$^{-1}$. Co-temporal photospheric magnetic field data obtained from the Helioseismic and Magnetic Imager (HMI) reveal that during such split-drift evolution, one of the loop points in the photosphere moves back and forth between nearby magnetic polarities. While the exact cause of this `split-drift' phenomenon is still unclear, the consistent patterns observed in its characteristics indicate that there may be a broader physical mechanism at play. This underscores the need for further investigation through both observational studies and numerical simulations.

astro-ph.SR↗

arXiv2025

Exploring the magnetic states in the one-band Hubbard model: Impact of long-range hoppings

Correlated electron systems with competing interactions provide a valuable platform for examining exotic magnetic phases. Theoretical models often focus on nearest-neighbor interactions, although long-range interactions can have a considerable impact on the behavior of the system, creating distinct and complicated magnetic phases. We investigate the consequences of competing interactions in a half-filled one-band Hubbard model on a simple cubic lattice, incorporating hopping processes up to third-nearest-neighbors, to explore the underlying magnetotransport properties. Our magnetic phase diagrams at low temperatures, obtained using semi-classical Monte Carlo analysis, reveal that the long-range interactions can disrupt one form of magnetic phase while creating a new type of magnetic order. For the nonperturbative regime (on-site Hubbard repulsive strength $U \sim$ bandwidth) the C-type antiferromagnetic ground state is preferred over the G-type antiferromagnetic phase when the interaction between second-nearest neighbor sites becomes significant to the nearest-neighbor interactions. However, interactions beyond the second-nearest-neighbors are required to stabilize the A-type antiferromagnetic ground state. Remarkably, at low temperatures, a highly correlated paramagnetic insulating phase develops at the intersection between the antiferromagnetic phases, which might promote a three-dimensional spin-liquid state.

cond-mat.str-el↗

arXiv2024

Microscopic study of interlayer magnetic coupling across the interface in antiferromagnetic bilayers

The enhancement of Neel temperature ($T_N$) of low-$T_{N}$ antiferromagnets in antiferromagnetic bilayers AF1/AF2, where the $T_N$ of AF1 is larger than AF2 (for example enhancement of $T_{N}$ of CoO in CoO/NiO or FeO in FeO/CoO), is a subject of considerable interest. One essential question needs to be answered in these bilayers: is the interfacial coupling a short-range one or long-range that mediates the effect of the AF1 layers on the magnetic properties of AF2 layer? To understand the systematics of the magnetic coupling across the interface, we investigate the plane-resolved magnetotransport properties of antiferromagnetic bilayers using an electron-hole symmetric one-band Hubbard model at half-filling, employing a semi-classical Monte Carlo method. In our model Hamiltonian calculations, we set Coulomb repulsion $U_{1} = 8$ to mimic high-$T_{N}$ AF1 layer, whereas we use $U_{2}$ = $2\times U_{1}$ to mimic the low-$T_{N}$ AF2 layer. Our calculations show that the $T_{N}$ of the low-$T_{N}$ antiferromagnet enhances substantially when it's thickness is small, similar to experiments, giving rise to single magnetic transition temperature of the bilayer system. These findings are well supported by a single peak in temperature-dependent specific heat. However, for larger thicknesses, the $T_{N}$ of the low-$T_{N}$ antiferromagnet approaches towards its bulk value and constituent antiferromagnetic layers align antiferromagnetically at two separate temperatures and two maxima are observed in specific heat data. Our calculations also show that the delocalization of moments is more or less confined near the interface indicating the short-ranged nature of the proximity effect. Our obtained results are consistent with the experimental observations. A detailed discussion of the modifications that will occur if we use $U_{1} = 8$ and $U_{2}$ = $0.5\times U_{1}$ will also be addressed.

cond-mat.str-el↗

arXiv2024

Bidirectional propagating brightenings in arch filament systems observed by Solar Orbiter/EUI

Arch filament systems (AFSs) are chromospheric and coronal manifestations of emerging magnetic flux. Using high spatial resolution observations taken at a high cadence by the Extreme Ultraviolet Imager (EUI) on board Solar Orbiter, we identified small-scale elongated brightenings within the AFSs. These brightenings appear as bidirectional flows along the threads of AFSs. For our study, we investigated the coordinated observations of the AFSs acquired by the EUI and the Atmospheric Imaging Assembly (AIA) on board SDO on 2022 March 4 and 17. We analyzed 15 bidirectional propagating brightenings from EUI 174 Å images. These brightenings reached propagating speeds of 100-150 km/s. The event observed on March 17 exhibits blob-like structures, which may be signatures of plasmoids and due to magnetic reconnection. In this case, we also observed counterparts in the running difference slit-jaw images in the 1400 Å passbands taken by the Interface Region Imaging Spectrograph (IRIS). Most events show co-temporal intensity variations in all AIA EUV passbands. Together, this implies that these brightenings in the AFSs are dominated by emission from cool plasma with temperatures well below 1 MK. The magnetograms taken by the Polarimetric and Helioseismic Imager (PHI) on board Solar Orbiter show signatures of flux emergence beneath the brightenings. This suggests that the events in the AFSs are triggered by magnetic reconnection that may occur between the newly emerging magnetic flux and the preexisting magnetic field structures in the middle of the AFSs. This would also give a natural explanation for the bidirectional propagation of the brightenings near the apex of the AFSs. The interaction of the preexisting field and the emerging flux may be important for mass and energy transfer within the AFSs.

astro-ph.SR↗

arXiv2024

Investigating coronal loop morphology and dynamics from two vantage points

Coronal loops serve as the fundamental building blocks of the solar corona. Therefore, comprehending their properties is essential in unraveling the dynamics of the Sun's upper atmosphere. In this study, we conduct a comparative analysis of the morphology and dynamics of a coronal loop observed from two different spacecraft: the High Resolution Imager (HRI$_{EUV}$) of the Extreme Ultraviolet Imager aboard the Solar Orbiter and the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory. These spacecraft were separated by 43$^{\circ}$ during this observation. The main findings of this study are: (1) The observed loop exhibits similar widths in both the HRI$_{EUV}$ and AIA data, suggesting that the cross-sectional shape of the loop is circular; (2) The loop maintains a uniform width along its entire length, supporting the notion that coronal loops do not exhibit expansion; (3) Notably, the loop undergoes unconventional dynamics, including thread separation and abrupt downward movement. Intriguingly, these dynamic features also appear similar in data from both spacecraft. Although based on observation of a single loop, these results raise questions about the validity of the coronal veil hypothesis and underscore the intricate and diverse nature of complexity within coronal loops.

astro-ph.SR↗

arXiv2023

Evolution of dynamic fibrils from the cooler chromosphere to the hotter corona

Dynamic fibrils (DFs) are commonly observed chromospheric features in solar active regions. Recent observations from the Extreme Ultraviolet Imager (EUI) aboard the Solar Orbiter have revealed unambiguous signatures of DFs at the coronal base, in extreme ultraviolet (EUV) emission. However, it remains unclear if the DFs detected in the EUV are linked to their chromospheric counterparts. Simultaneous detection of DFs from chromospheric to coronal temperatures could provide important information on their thermal structuring and evolution through the solar atmosphere. In this paper, we address this question by using coordinated EUV observations from the Atmospheric Imaging Assembly (AIA), Interface Region Imaging Spectrograph (IRIS), and EUI to establish a one-to-one correspondence between chromospheric and transition region DFs (observed by IRIS) with their coronal counterparts (observed by EUI and AIA). Our analysis confirms a close correspondence between DFs observed at different atmospheric layers, and reveals that DFs can reach temperatures of about 1.5 million Kelvin, typical of the coronal base in active regions. Furthermore, intensity evolution of these DFs, as measured by tracking them over time, reveals a shock-driven scenario in which plasma piles up near the tips of these DFs and, subsequently, these tips appear as bright blobs in coronal images. These findings provide information on the thermal structuring of DFs and their evolution and impact through the solar atmosphere.

astro-ph.SR↗

arXiv2023

The Role of High-frequency Transverse Oscillations in Coronal Heating

Transverse oscillations that do not show significant damping in solar coronal loops are found to be ubiquitous. Recently, the discovery of high-frequency transverse oscillations in small-scale loops has been accelerated by the Extreme Ultraviolet Imager onboard Solar Orbiter. We perform a meta-analysis by considering the oscillation parameters reported in the literature. Motivated by the power law of the velocity power spectrum of propagating transverse waves detected with CoMP, we consider the distribution of energy fluxes as a function of oscillation frequencies and the distribution of the number of oscillations as a function of energy fluxes and energies. These distributions are described as a power law. We propose that the power law slope ($δ=-1.40$) of energy fluxes depending on frequencies could be used for determining whether high-frequency oscillations dominate the total heating ($δ< 1$) or not ($δ> 1$). In addition, we found that the oscillation number distribution depending on energy fluxes has a power law slope of $α=1.00$, being less than 2, which means that oscillations with high energy fluxes provide the dominant contribution to the total heating. It is shown that, on average, higher energy fluxes are generated from higher frequency oscillations. The total energy generated by transverse oscillations ranges from about $10^{20}$ to $10^{25}$ erg, corresponding to the energies for nanoflare ($10^{24}-10^{27}$ erg), picoflare ($10^{21}-10^{24}$ erg), and femtoflare ($10^{18}-10^{21}$ erg). The respective slope results imply that high-frequency oscillations could provide the dominant contribution to total coronal heating generated by decayless transverse oscillations.

astro-ph.SR↗

arXiv2023

Slow Solar Wind Connection Science during Solar Orbiter's First Close Perihelion Passage

The Slow Solar Wind Connection Solar Orbiter Observing Plan (Slow Wind SOOP) was developed to utilise the extensive suite of remote sensing and in situ instruments on board the ESA/NASA Solar Orbiter mission to answer significant outstanding questions regarding the origin and formation of the slow solar wind. The Slow Wind SOOP was designed to link remote sensing and in situ measurements of slow wind originating at open-closed field boundaries. The SOOP ran just prior to Solar Orbiter's first close perihelion passage during two remote sensing windows (RSW1 and RSW2) between 2022 March 3-6 and 2022 March 17-22, while Solar Orbiter was at a heliocentric distance of 0.55-0.51 and 0.38-0.34 au from the Sun, respectively. Coordinated observation campaigns were also conducted by Hinode and IRIS. The magnetic connectivity tool was used, along with low latency in situ data, and full-disk remote sensing observations, to guide the target pointing of Solar Orbiter. Solar Orbiter targeted an active region complex during RSW1, the boundary of a coronal hole, and the periphery of a decayed active region during RSW2. Post-observation analysis using the magnetic connectivity tool along with in situ measurements from MAG and SWA/PAS, show that slow solar wind, with velocities between 210 and 600 km/s, arrived at the spacecraft originating from two out of the three of the target regions. The Slow Wind SOOP, despite presenting many challenges, was very successful, providing a blueprint for planning future observation campaigns that rely on the magnetic connectivity of Solar Orbiter.

astro-ph.SR↗

arXiv2023

Slow solar wind sources. High-resolution observations with a quadrature view

The origin of the slow solar wind is still an open issue. One possibility that has been suggested is that upflows at the edge of an active region can contribute to the slow solar wind. We aim to explain how the plasma upflows are generated, which mechanisms are responsible for them, and what the upflow region topology looks like. We investigated an upflow region using imaging data with the unprecedented temporal (3s) and spatial (2 pixels = 236km) resolution that were obtained on 30 March 2022 with the 174Å of the Extreme-Ultraviolet Imager (EUI)/High Resolution Imager (HRI) on board Solar Orbiter. During this time, the EUI and Earth-orbiting satellites (Solar Dynamics Observatory, Hinode, and the Interface Region Imaging Spectrograph, IRIS) were located in quadrature (92 degrees), which provides a stereoscopic view with high resolution. We used the Hinode/EIS (Fe XII) spectroscopic data to find coronal upflow regions in the active region. The IRIS slit-jaw imager provides a high-resolution view of the transition region and chromosphere. For the first time, we have data that provide a quadrature view of a coronal upflow region with high spatial resolution. We found extended loops rooted in a coronal upflow region. Plasma upflows at the footpoints of extended loops determined spectroscopically through the Doppler shift are similar to the apparent upward motions seen through imaging in quadrature. The dynamics of small-scale structures in the upflow region can be used to identify two mechanisms of the plasma upflow: Mechanism I is reconnection of the hot coronal loops with open magnetic field lines in the solar corona, and mechanism II is reconnection of the small chromospheric loops with open magnetic field lines in the chromosphere or transition region. We identified the locations in which mechanisms I and II work.

astro-ph.SR↗

arXiv2022

Detection of Solar Filaments using Suncharts from Kodaikanal Solar Observatory Archive Employing a Clustering Approach

With over 100 years of solar observations, the Kodaikanal Solar Observatory (KoSO) is a one-of-a-kind solar data repository in the world. Among its many data catalogues, the `suncharts' at KoSO are of particular interest. These Suncharts (1904-2020) are coloured drawings of different solar features, such as sunspots, plages, filaments, and prominences, made on papers with a Stonyhurst latitude-longitude grid etched on them. In this paper, we analyze this unique data by first digitizing each suncharts using an industry-standard scanner and saving those digital images in high-resolution `.tif' format. We then examine the Cycle~19 and Cycle~20 data (two of the strongest cycles of the last century) with the aim of detecting filaments. To this end, we employed `k-means clustering' method and obtained different filament parameters such as position, tilt angle, length, and area. Our results show that filament length (and area) increases with latitude and the pole-ward migration is clearly dominated by a particular tilt sign. Lastly, we cross-verified our findings with results from KoSO digitized photographic plate database for the overlapping time period and obtained a good agreement between them. This work, acting as a proof-of-the-concept, will kick-start new efforts to effectively use the entire hand-drawn series of multi-feature, full-disk solar data and enable researchers to extract new sciences, such as the generation of pseudo magnetograms for the last 100 years.

astro-ph.SR↗

arXiv2022

Signatures of dynamic fibrils at the coronal base: Observations from Solar Orbiter/EUI

The solar chromosphere hosts a wide variety of transients, including dynamic fibrils (DFs) that are characterised as elongated, jet-like features seen in active regions, often through H$α$ diagnostics. So far, these features have been difficult to identify in coronal images primarily due to their small size and the lower spatial resolution of the current EUV imagers. Here we present the first unambiguous signatures of DFs in coronal EUV data using high-resolution images from the Extreme Ultraviolet Imager (EUI) on board Solar Orbiter. Using the data acquired with the 174~Å High Resolution Imager (HRI$_{EUV}$) of EUI, we find many bright dot-like features (of size 0.3-0.5 Mm) that move up and down (often repeatedly) in the core of an active region. In a space-time map, these features produce parabolic tracks akin to the chromospheric observations of DFs. Properties such as their speeds (14 km~s$^{-1}$), lifetime (332~s), deceleration (82 m~s$^{-2}$) and lengths (1293~km) are also reminiscent of the chromospheric DFs. The EUI data strongly suggest that these EUV bright dots are basically the hot tips (of the cooler chromospheric DFs) that could not be identified unambiguously before because of a lack of spatial resolution.

astro-ph.SR↗

arXiv2022

SPICE PSF Correction: General Framework and Capability Demonstration

We present a new method of removing PSF artifacts and improving the resolution of multidimensional data sources including imagers and spectrographs. Rather than deconvolution, which is translationally invariant, this method is based on sparse matrix solvers. This allows it to be applied to spatially varying PSFs and also to combining observations from instruments with radically different spatial, spectral, or thermal response functions (e.g., SDO/AIA and RHESSI). It was developed to correct PSF artifacts in Solar Orbiter SPICE, so the motivation, presentation of the method, and the results revolve around that application. However, it can also be used as a more robust (e.g., WRT a varying PSFs) alternative to deconvolution of 2D image data and similar problems, and is relevant to more general linear inversion problems.

astro-ph.SR↗