arXiv subjects

Sripan Mondal

Publications and source records attributed to Sripan Mondal.

9 recordsLinked to original sources

arXiv2026

A Numerical Experiment on Oscillatory Magnetic Reconnection in a Laboratory Plasma System Driven by Alternating Currents

Using the open source MPI-AMRVAC framework, we study oscillatory reconnection in a laboratory plasma, which occurs when a magnetic null is perturbed by incoming fast magnetoacoustic waves driven by an alternating current. The magnetic null region collapses to first form a $y$-directed current sheet that later changes its orientation to the $x$-direction. The $x$-directed current sheet has smaller enhanced thermal pressure and out-of-plane current than the $y$-directed current sheet. The Hall effect produces an out-of-plane plasma flow that evolves with a time lag with respect to the enhanced thermal pressure and out-of-plane current density. Increasing the amplitude of the alternating current produces higher thermal pressure, out-of-plane current density, and out-of-plane plasma flow, while the first peaks of thermal pressure and out-of-plane current density occur earlier.

physics.plasm-ph↗

arXiv2026

Interaction of Fast Magnetoacoustic Wave with the Localized Coronal Null and Generation of the Energetic Alfv\'en Wave Packet

In the present paper, we have performed 2.5D resistive magnetohydrodynamic simulations of the interaction of a fast magnetoacoustic wave with a localized coronal magnetic null point. As a result, an Alfv\'en wave packet is generated by the mode conversion when a fast magnetoacoustic perturbation interacts with the null point. The field-aligned plasma flows are also generated due to the non-linear effects. When the fast mode wavefront interacts with the null, some parts of this wavefront get refracted around it, while some other part is trapped at the null region. Subsequently, the velocity fluctuation out of the plane and in-phase magnetic field fluctuations have evolved and propagated with the local Alfv\'en speed along the separatrixes at one side of the coronal null region. The resulting disturbance behaves as an incompressible and energetic Alfv\'en wave packet. A secondary fast magnetoacoustic wave is also produced and propagates. In the synthetic SDO/AIA observations, no intensity fluctuations are evident in the region where the Alfv\'en wave packet propagates, while the fast magnetoacoustic wave fronts are clearly evident. Our results suggest that given the appropriate physical conditions at the null, when the fast mode wave is incident, Alfv\'en packets can be excited due to the mode conversion, further carrying substantial momentum and energy flux in the solar corona.

astro-ph.SR↗

arXiv2025

Generation of Surface Sausage Oscillations of a Current Sheet and Propagating Magnetoacoustic Waves by Impulsive Reconnection

Magnetic reconnection and Magnetohydrodynamic (MHD) waves may well be both playing a role in coronal heating. In this paper, we simulate reconnection in the corona as a response to the convergence of opposite-polarity magnetic sources at the base of the corona. A current sheet forms at a magnetic null and undergoes impulsive bursty reconnection which drives natural modes of oscillation of the current sheet by a process of symbiosis. These are leaky surface sausage modes which cause the length of the current sheet to oscillate. Interaction of the oscillations and reconnection outflows with the magnetic Y-points at the ends of the sheet acts as sources for magnetoacoustic waves. Fast-mode waves propagate outwards into the coronal environment, while slow-mode waves propagate along the separatrices extending from the ends of the current sheet. The periodicities for sausage oscillations of the current sheet, for the current sheet length, and for the propagating large-scale magnetoacoustic waves are all estimated to be approximately 91 s for the parameters of our experiment.

astro-ph.SR↗

arXiv2025

Localized Heating and Dynamics of the Solar Corona due to a Symbiosis of Waves and Reconnection

The Sun's outer atmosphere, the corona, is maintained at mega-Kelvin temperatures and fills the heliosphere with a supersonic outflowing wind. The dissipation of magnetic waves and direct electric currents are likely to be the most significant processes for heating the corona, but a lively debate exists on their relative roles. Here, we suggest that the two are often intrinsically linked, since magnetic waves may trigger current dissipation, and impulsive reconnection can launch magnetic waves. We present a study of the first of these processes by using a 2D physics-based numerical simulation using the Adaptive Mesh Refined (AMR) Versatile Advection Code (VAC). Magnetic waves such as fast magnetoacoustic waves are often observed to propagate in the large-scale corona and interact with local magnetic structures. The present numerical simulations show how the propagation of magnetic disturbances towards a null point or separator can lead to the accumulation of the electric currents. Lorentz forces can laterally push and vertically stretch the magnetic fields, forming a current sheet with a strong magnetic-field gradient. The magnetic field lines then break and reconnect, and so contribute towards coronal heating. Numerical results are presented that support these ideas and support the concept of a symbiosis between waves and reconnection in heating the solar corona.

astro-ph.SR↗

arXiv2024

Dynamics and Energetics of Resistive, Thermally Conductive, and Radiative Plasma in Coronal Current Sheets due to Asymmetric External Perturbation

We study the asymmetric interaction of wave-like velocity perturbation with a coronal current sheet (CS) in the presence of resistivity, thermal conduction (TC) and radiative cooling (RC). We analyze the dynamics and energetics of CS in four cases, namely, (i) no energy loss, (ii) TC only, (iii) RC only and, (iv) TC+RC. Before fragmentation, thinning and elongation of the CS are found to be identical in all four cases and therefore independent of presence or absence of energy loss effects. Onset times, corresponding Lundquist numbers and aspect ratios suggest that TC advances the onset of fragmentation while RC has the opposite effect in comparison to absence of energy losses. Reconnection takes place at a higher rate in presence of TC and TC+RC in the tearing unstable CS. The speed of plasmoids are also found to be higher under the effect of TC and TC+RC. In presence of TC and TC+RC, average density becomes higher within the tearing unstable CS than in other two cases. As expected, estimated average temperature is increasing with highest and lowest rate in absence of energy losses and in presence of both TC and RC respectively. After the onset of fragmentation, the rate of decrement of average magnetic energy density and increment of average kinetic energy density becomes higher in presence of TC and TC+RC than in other two cases. Thus we conclude that presence of energy loss mechanisms critically influence the dynamics, energetics, and plasmoid formation within a reconnecting coronal CS.

astro-ph.SR↗

arXiv2024

Generation of fast magnetoacoustic waves in the corona by impulsive bursty reconnection

Fast-mode magnetohydrodynamic (MHD) waves in the solar corona are often known to be produced by solar flares and eruptive prominences. We here simulate the effect of the interaction of an external perturbation on a magnetic null in the solar corona which results in the formation of a current sheet (CS). Once the CS undergoes a sufficient extension in its length and squeezing of its width, it may go unstable to the formation of multiple impulsive plasmoids. Eventually, the plasmoids merge with one another to form larger plasmoids and/or are expelled from the sheet. The formation, motion and coalescence of plasmoids with each other and with magnetic Y-points at the outer periphery of the extended CS are found to generate wave-like perturbations. An analysis of the resultant quasi-periodic variations of pressure, density, velocity and magnetic field at certain locations in the model corona indicate that these waves are predominantly fast-mode magnetoacoustic waves. For typical coronal parameters, the resultant propagating waves carry an energy flux of $\mathrm{10^{5}~\mathrm{erg~cm^{-2}~s^{-1}}}$ to a large distance of at least 60 Mm away from the current sheet. In general, we suggest that both waves and reconnection play a role in heating the solar atmosphere and driving the solar wind and may interact with one another in a manner that we refer to as a $"$Symbiosis of WAves and Reconnection (SWAR)$"$.

astro-ph.SR↗

arXiv2024

2.5-D MHD Simulation of the Formation and Evolution of Plasmoids in Coronal Current Sheets

In the present paper, using MPI-AMRVAC, we perform a 2.5-D numerical MHD simulation of the dynamics and associated thermodynamical evolution of an initially force-free Harris current sheet subjected to an external velocity perturbation under the condition of uniform resistivity. The amplitude of the magnetic field is taken to be 10 Gauss, typical of the solar corona. We impose a Gaussian velocity pulse across this current sheet mimicking the interaction of fast magnetoacoustic waves with a current sheet in corona. This leads to a variety of dynamics and plasma processes in the current sheet, which is initially quasi-static. The initial pulse interacts with the current sheet and splits into a pair of counter-propagating wavefronts, which forms a rarefied region and leads to inflow and a thinning of the current sheet. The thinning results in Petschek-type magnetic reconnection followed by tearing instability and plasmoid formation. The reconnection outflows containing outward-moving plasmoids have accelerated motions with velocities ranging from 105-303 km/s. The average temperature and density of the plasmoids are found to be 8 MK and twice the background density of the solar corona, respectively. These estimates of velocity, temperature and density of plasmoids are similar to values reported from various solar coronal observations. Therefore, we infer that the external triggering of a quasi-static current sheet by a single velocity pulse is capable of initiating magnetic reconnection and plasmoid formation in the absence of a localized enhancement of resistivity in the solar corona.

astro-ph.SR↗

arXiv2023

Reconnection generated plasma flows in the quasi-separatrix layer in localised solar corona

Multiwavelength observations of the propagating disturbances (PDs), discovered by Atmospheric Imaging Assembly (AIA) onboard Solar Dynamics Observatory (SDO), are analyzed to determine its driving mechanism and physical nature. Two magnetic strands in the localised corona are observed to approach and merge with each other followed by the generation of brightening, which further propagates in a cusp-shaped magnetic channel. Differential emission measure analysis shows an occurrence of heating in this region-of-interest (ROI). We extrapolate potential magnetic field lines at coronal heights from observed Helioseismic and Magnetic Imager (HMI) vector magnetogram via Green's function method using MPI-AMRVAC. We analyze the field to locate magnetic nulls and quasi-separatrix layers (QSLs) which are preferential locations for magnetic reconnection. Dominant QSLs including a magnetic null are found to exist and match the geometry followed by PDs, therefore, it provides conclusive evidence of magnetic reconnection. In addition, spectroscopic analysis of Interface Region Imaging Spectrograph (IRIS) Si IV 1393.77 Å line profiles show a rise of line-width in the same time range depicting presence of mass motion in the observed cusp-shaped region. PDs are observed to exhibit periodicities of around four minutes. The speeds of PDs measured by Surfing Transform Technique are almost close to each other in four different SDO/AIA bandpasses, i.e., 304, 171, 193 and 131 Å excluding the interpretation of PDs in terms of slow magnetoacoustic waves. We describe comprehensively the observed PDs as quasi-periodic plasma flows generated due to periodic reconnection in vicinity of a coronal magnetic null.

astro-ph.SR↗

arXiv2021

RMS-Flux Relation and Disc-Jet Connection in Blazars in the Context of the Internal Shocks Model

Recent analysis of blazar variability has revealed a proportionality between the mean flux and the root mean squared (rms) fluctuations about the mean flux. Although such rms-flux relation has been previously observed in the accretion disc/corona variability of X-ray binaries and Seyfert galaxies, and has been extensively modelled, its emergence in the jet light curves of blazars calls for a revised theoretical understanding of this feature. In this work, we analyse the time variability properties of realistic multi-wavelength jet light curves, simulated in the context of a simplified version of the internal shocks model, particularly focusing on the rms-flux relation. These shocks accelerate the jet electrons to relativistic energies, which then cool radiatively via synchrotron and inverse-Compton processes. We find that the rms-flux relation may be consistently recovered in the cases, in which the shocks have different amplitudes based on the speed of the colliding blobs generating them as opposed to all shocks having the same amplitude. We observe that the slope of the rms-flux relation depends on the wavelength at which the variability is observed and the energy distribution of the electron population. We find that the accretion disc and the jet variability are anti-correlated, with the latter lagging that of the disc. Our results provide crucial constraints on the physical properties of the jet, and the mode of connection through which the accretion disc and jet may be related.

astro-ph.HE↗