arXiv subjects

Ramit Bhattacharyya

Publications and source records attributed to Ramit Bhattacharyya.

13 recordsLinked to original sources

arXiv2026

Observations of a Twin Pair of Atypical Solar Flares and a Magnetic-reconnection Scenario

We present observations and a magnetic-reconnection scenario of a twin pair of "atypical flares" that occurred on 2022 April 22 in a quadrupolar magnetic configuration formed by two active regions. The spatio-temporal evolution of the two flares is examined using images from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO), and from the ground-based Multi-Application Solar Telescope (MAST) in Udaipur, India. Characteristic of atypical flares and indicative of slipping reconnection, the ribbons of each flare (1) do not spread apart and (2) grow longer by sequential brightening of new flare kernels. The two atypical flares are homologous and plausibly have homologous triggers. There are four additional pairs of flare ribbons, each from a different flaring event that releases much less energy than the atypical flares. Two of these four pairs are produced by precursors, each possibly triggering one of the two atypical flares. The remaining two pairs accompany a filament activation, occurring twice within the span of the two atypical flares. Using a nonlinear force-free field (NLFFF) extrapolation model, we approximate the coronal magnetic field and find two quasi-separatrix layers (QSLs) that are nearly rooted in the flare ribbons. The observations and the extrapolated field together suggest a scenario in which the nearly simultaneous occurrence of many reconnections between magnetic field lines crossing at small angles (slipping reconnection) within each of the two QSLs produces the observed pair of atypical flares.

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arXiv2026

Investigation of magnetic topology and triggering mechanisms of a C-class flare and active-region blowout jet

Coronal jets are collimated plasma eruptions which are ubiquitous in the solar atmosphere. Believed to be triggered by magnetic reconnection, these jets can contribute to various phenomena, including coronal heating and particle acceleration. Coronal jets are a contemporary area of research with their onset mechanism meriting further attention. Importantly, a subclass of jets, the blowout jets, are particularly interesting because of their broad spire, suggesting substantial three-dimensional (3D) reconnection between open and closed field lines involving 3D null points. Consequently, here we explore the onset of a blowout jet associated with Active Region (AR) SPoCA 29093 detected by Spatial Possibilistic Clustering Algorithm (SPoCA). This AR produced a C1.1-class flare on 10 November 2022 and we investigate it using a data-constrained magnetohydrodynamic simulation initiated with a non force-free-field (NFFF) extrapolation of the photospheric magnetic field. Key elements of the extrapolated field lines are the presence of a 3D null and a magnetic flux rope (MFR) co-located with the jet activity region, the evolution of which is further traced in the simulation. The simulation suggests that magnetic reconnection is responsible for the evolution of the MFR, leading to a near-simultaneous onset of the flare and jet as observed by the AIA/SDO. In particular, the simulation shows spontaneous creation and annihilation of 3D null pairs via magnetic reconnection near the jet region. Such spontaneous null pair generation, in principle, can trigger or contribute to coronal jets; opening up a new avenue for further research.

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arXiv2025

On the Magnetic Reconnection and its Properties during a Flare Using a Magnetohydrodynamics Simulation

We study the magnetic reconnection during a flare by investigating flare ribbon dynamics using observations and data-constrained magnetohydrodynamics (MHD) simulation. In particular, we estimate the reconnection flux and the reconnection flux rates using flare ribbons of an M1.1 flare hosted by the active region 12184 utilizing the technique developed by Qiu et al. (2002, ApJ, 565, 1335). The reconnection flux and corresponding flux rates are found to be 10^20 Mx and 10^18 Mx/s respectively. To understand the flare onset and the origin of flare ribbons, we perform an MHD simulation initiated by the non-force-free-field extrapolation. Importantly, the extrapolated configuration identifies a three-dimensional (3D) magnetic neutral point and a flux rope in the flaring region, which is crucial to the flaring activity. The reconnection initiates at the null point and, subsequently the flux rope rises and appears to reconnect there, which is favorable for the eruption of the filament. The surrounding field lines also seem to take part in the null point reconnection. In later stage, a current sheet is formed below the null point ensuing a secondary reconnection near an X-type topology, further contributing to the energy release process in the flare. We trace the footpoint evolution of the field lines lying over the flare ribbons and find a significant similarity between the observed flare ribbons and the evolution of footpoints computed from the MHD simulation. We estimated induced electric field during the flare and found it to be $\approx$ .52 V/cm, a slight less value, as per many past literatures. Additional findings are the enhancement of vertical current density near the flaring ribbons, a signature of successive reconnections near the null point. Overall, the present work contributes to the understanding of the ribbon formation in a flaring process and the involved magnetic reconnection.

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arXiv2025

Data-Constrained Magnetohydrodynamics Simulation of a Confined X-class Flare in NOAA Active Region 11166

In this paper, we present a magnetohydrodynamics simulation of NOAA active region 11166 to understand the origin of a confined X-class flare that peaked at 23:23 UT on 2011 March 9. The simulation is initiated with a magnetic field extrapolated from the corresponding photospheric magnetogram using a non-force-free-field extrapolation technique. Importantly, the initial magnetic configuration identifies three-dimensional (3D) magnetic nulls and quasi-separatrix layers (QSLs), which nearly agree with the bright structures appeared in multi-wavelength observations. The Lorentz force associated with the extrapolated field self-consistently generates the dynamics that leads to the magnetic reconnections at the 3D nulls and the QSLs. These reconnections are found to contribute to the pre-flare activities and, ultimately, lead to the development of the flare ribbons. Notably, the anchored spine of the 3D null and the complete absence of flux rope in the flaring region are congruent with the confined nature of the flare. Furthermore, the simulation also suggests the role of reconnections at the 3D null with an open spine in the onset of a jet away from the flaring site.

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arXiv2024

Exploring the generation and annihilation of three dimensional nulls through MHD simulations in initially chaotic magnetic field devoid of nulls

Three-dimensional (3D) magnetic nulls are abundant in the solar atmosphere, as been firmly established through contemporary observations. They are established to be important magnetic structures in, for example, jets and circular ribbon flares. While simulations and extrapolations support this, the mechanisms behind 3D null generation remain an open question. Recent magnetohydrodynamics (MHD) simulations propose that magnetic reconnection is responsible for both generating and annihilating 3D nulls, a novel concept. However, these simulations began with initial magnetic fields already supporting pre-existing nulls, raising the question of whether magnetic reconnection can create nulls in fields initially devoid of them. Previously, this question was briefly explored in a simulation with an initial chaotic magnetic field. However, the study failed to precisely identify locations, topological degrees, and natures (spiral or radial) of nulls, and it approximated magnetic reconnection without fully tracking field line in time. In this paper these findings are revisited in light of recent advancements and tools used to locate and trace nulls, along with the tracing of field lines, through which the concept of generation/annihilation of 3D nulls from chaotic fields is established in a precise manner.

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arXiv2024

Generation and annihilation of three dimensional magnetic nulls in extrapolated solar coronal magnetic field: Data-based Implicit Large Eddy Simulation

Three-dimensional magnetic nulls are the points where magnetic field vanishes and are preferential sites for magnetic reconnection: a process which converts magnetic energy into heat and accelerates charged particles along with a rearrangement of magnetic field lines. In the solar corona, the reconnections manifest as coronal transients including solar flares, coronal mass ejections and coronal jets. The nulls are generally found to be collocated with complex active regions on the solar photosphere. Extrapolation of magnetic field from corresponding photospheric magnetogram indicate an abundance of these nulls in solar atmosphere. Nevertheless, their generation is still not well understood. Recently, Maurya et al. (2023) have demonstrated magnetic reconnection to be a cause for generation and annihilation of magnetic nulls through magnetohydrodynamics simulation, where the initial magnetic field is idealized to have a single radial null. This article further extends the study in a more realistic scenario where the initial magnetic field is constructed by extrapolating photospheric magnetogram data and hence, incorporates field line complexities inherent to a complex active region. For the purpose, the active region NOAA 11977 hosting a C6.6 class flare is selected. The simulation is initiated using non-force-free extrapolated magnetic field from the photospheric vector magnetogram at around 02:48:00 UT on 17 February 2014, 16 minutes before the flare peak. The generation, annihilation and dynamics of nulls are explored by a complimentary usage of trilinear null detection technique and tracing of magnetic field line dynamics. It is found that the nulls can spontaneously generate/annihilate in pairs while preserving the topological degree and can have observational implications like footpoint brightenings. Magnetic reconnection is found to be the cause of such generation and annihilation.

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arXiv2024

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

Self-organization in continuous systems is associated with dissipative processes. In particular, for magnetized plasmas, it is known as magnetic relaxation, where the magnetic energy is converted into heat and kinetic energy of flow through the process of magnetic reconnection. An example of such a system is the solar corona, where reconnection manifests as solar transients like flares and jets. Consequently, toward investigation of plasma relaxation in solar transients, we utilize a novel approach of data-constrained MHD simulation for an observed solar flare. The selected active region NOAA 12253 hosts a GOES M1.3 class flare. The investigation of extrapolated coronal magnetic field in conjunction with the spatiotemporal evolution of the flare reveals a hyperbolic flux tube (HFT), overlying the observed brightenings. MHD simulation is carried out with the EULAG-MHD numerical model to explore the corresponding reconnection dynamics. The overall simulation shows signatures of relaxation. For a detailed analysis, we consider three distinct sub-volumes. We analyze the magnetic field line dynamics along with time evolution of physically relevant quantities like magnetic energy, current density, twist, and gradients in magnetic field. In the terminal state, none of the sub-volumes are seen to reach a force-free state, thus remaining in non-equilibrium, suggesting the possibility of further relaxation. We conclude that the extent of relaxation depends on the efficacy and duration of reconnection, and hence, on the energetics and time span of the flare.

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arXiv2023

Hall effect on the magnetic reconnections during the evolution of a three-dimensional magnetic flux rope

We present a novel Hall magnetohydrodynamics (HMHD) numerical simulation of a three-dimensional (3D) magnetic flux rope (MFR) -- generated by magnetic reconnections from an initial 3D bipolar sheared field. Magnetic reconnections during the HMHD evolution are compared with the MHD. In both simulations, the MFRs generate as a consequence of the magnetic reconnection at null points which has not been realized in contemporary simulations. Interestingly, the evolution is faster and more intricate in the HMHD simulation. Repetitive development of the twisted magnetic field lines (MFL) in the vicinity of 3D nulls (reconnection site) is unique to the HMHD evolution of the MFR. The dynamical evolution of magnetic field lines around the reconnection site being affected by the Hall forcing, correspondingly affects the large-scale structures.

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arXiv2022

Magnetohydrodynamics evolution of three-dimensional magnetic null in NOAA active region 11515 initiated using non-force-free field extrapolation

Magnetohydrodynamics simulation of active region NOAA 11515 is performed to examine the initiation of the M5.6 flaring event that starts around 10:43 UT on 2012 July 2. The simulation is conducted using an extrapolated non-force-free magnetic field generated from the photospheric vector magnetogram of the active region as the initial magnetic field. The magnetic field shows the presence of a three-dimensional (3D) magnetic null with the corresponding dome overlying a filament and a low-lying magnetic flux rope, observed in 304~Å~ and 131~Å~ respectively. The simulated dynamics, triggered by the initial Lorentz force, lead to the bifurcations of the flux rope, which is similar to the observed bifurcation in the 131 Å~ brightenings. Additionally, the rope exhibits a rise and reconnects at the 3D null. These reconnections convert field lines of the rope into the anchored outer spine of the 3D null -- explaining the occurrence of a nearby confined C-class flare. Further, the results show that the field lines of the flux rope reach the vicinity of the filament and become non-parallel to the field lines of the filament. This initiates the reconnections between the rope and the field lines of the filament -- activating the filament for the eruption. This interesting interaction of the flux rope and filament seems to contribute to the onset of the M-class flare.

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arXiv2021

Comparison of the Hall Magnetohydrodynamics and Magnetohydrodynamics evolution of a flaring solar active region

This work analyzes the Hall magnetohydrodynamics (HMHD) and magnetohydrodynamics (MHD) numerical simulations of a flaring solar active region as a testbed while idealizing the coronal Alfvén speed to be of two orders of magnitude lesser. HMHD supports faster magnetic reconnection and shows richer complexity in magnetic field line evolution compared to the MHD. The magnetic reconnections triggering the flare are explored by numerical simulations augmented with relevant multi-wavelength observations. The initial coronal magnetic field is constructed by non-force-free extrapolation of photospheric vector magnetic field. Magnetic structure involved in the flare is identified to be a flux rope, with its overlying magnetic field lines constituting the quasi-separatrix layers (QSLs) along with a three-dimensional null point and a null line. Compared to the MHD simulation, the HMHD simulation shows a higher and faster ascend of the rope together with the overlying field lines, which further reconnect at the QSL located higher up in the corona. The foot points of the field lines match better with the observations for the HMHD case with the central part of the flare ribbon located at the chromosphere. Additionally, field lines are found to rotate in a circular pattern in the HMHD, whereas no such rotation is seen in the MHD results. Interestingly, plasma is also observed to be rotating in a co-spatial chromospheric region, which makes the HMHD simulation more credible. Based on the aforementioned agreements, HMHD simulation is found to agree better with observations and, thus, opens up a novel avenue to explore.

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arXiv2020

Magnetic reconnections in the presence of three-dimensional magnetic nulls and quasi-separatrix layers

Three-dimensional (3D) magnetohydrodynamic simulations are carried out to explore magnetic reconnections in the presence of 3D magnetic nulls and quasi-separatrix layers (QSLs). The initial magnetic fields are created by superposing uniform vertical magnetic fields of two different magnitudes on a linear force-free field. The interior of the numerical box contains two 3D nulls with separatrix domes separated by a quasi-separator (or hyperbolic flux tube) with QSLs. In the first simulation, the uniform vertical field is so large that the nulls are located at low heights and the domes are separate. Initially unbalanced Lorentz forces drive rotational flows that form strong electric currents and strong torsional fan reconnection at the 3D nulls and weak QSL reconnection at the hyperbolic flux tube. Flipping or slipping of field lines is observed in both cases. In the second simulation, with a weaker vertical field and larger domes, the separatrix surfaces meet at the central quasi-separator and their rotation drives stronger QSL reconnection than before.

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arXiv2020

Evolution of three-dimensional coherent structures in Hall magnetohydrodynamics

The work extends the computational model EULAG-MHD to include Hall magnetohydrodynamics (HMHD)---important to explore physical systems undergoing fast magnetic reconnection at the order of the ion inertial length scale. Examples include solar transients along with reconnections in magnetosphere, magnetotail and laboratory plasmas. The paper documents the results of two distinct sets of implicit large-eddy simulations in the presence and absence of the Hall forcing term, initiated with an unidirectional sinusoidal magnetic field. The HMHD simulation while benchmarking the code also emphasizes the complexity of three dimensional (3D) evolution over its two dimensional (2D) counterpart. The magnetic reconnections onset significantly earlier in HMHD. Importantly, the magnetic field generated by the Hall term breaks any inherent symmetry, ultimately making the evolution 3D. The resulting 3D reconnections develop magnetic flux ropes and magnetic flux tubes. Projected on the reconnection plane, the ropes and tubes appear as magnetic islands, which later break 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 HMHD, and thus verify our extension of the EULAG-MHD model. The second set explores the influence of the Hall forcing on generation and ascend of a magnetic flux rope from sheared magnetic arcades---a novel scenario instructive in understanding the coronal transients. The rope evolves through intermediate complex structures, ultimately breaking locally because of reconnections. Interestingly, the breakage occurs earlier in the presence of the Hall term, signifying faster dynamics leading to magnetic topology favorable for reconnections.

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arXiv2020

Solar Radio Observation Using CALLISTO at the USO/PRL, Udaipur

This paper presents a detailed description of various subsystems of CALLISTO solar radio spectrograph installed at the USO/PRL. In the front-end system, a log periodic dipole antenna (LPDA) is designed for the frequency range of 40-900 MHz. In this paper LPDA design, its modifications, and simulation results are presented. We also present some initial observations taken by CALLISTO at Udaipur.

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