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• Bate, W.; Gordovskyy, M.; Prasad, Avijeet; Brun, A. S.; Strugarek, A. & Sieyra, M. V. [Vis alle 10 forfattere av denne artikkelen] (2026). Energetics and Emission in a Simulated Solar Flare Initialized by a Non-force-free Magnetic Field. The Astrophysical Journal (ApJ). ISSN 0004-637X. 1006(2). doi: 10.3847/1538-4357/ae7c69. Fulltekst i vitenarkiv Vis sammendrag

  Solar flare simulations are commonly initialised using nonlinear force-free field (NLFF) extrapolations derived from photospheric vector magnetograms. However, the force-free assumption neglects plasma forces and may limit the available free magnetic energy. In this work, we perform a controlled comparison of two three-dimensional resistive magnetohydrodynamic simulations of the X2.1-class flare that occurred on 2011 September 6 in NOAA Active Region 11283. The simulations differ only in their initial magnetic configuration: one is based on a conventional NLFF extrapolation, while the other employs a non-force-free extrapolation. Both models are evolved in an identical stratified atmosphere using the same numerical framework, enabling direct assessment of how the initial magnetic assumptions influence flare dynamics and energetics. We find that the non-force-free model undergoes more extensive magnetic restructuring and releases approximately twice as much magnetic energy (≈4.4 × 10^31 erg) as the NLFF case (≈2.3 × 10^31 erg), bringing the energy budget into closer agreement with expectations for X-class flares. Synthetic extreme-ultraviolet emission in the 94 Å channel is computed for both simulations and compared with observations from the Solar Dynamics Observatory. The non-force-free model produces a brighter and more spatially extended emission structure that more closely resembles the observed flare morphology and light curve. These results demonstrate that assumptions made in constructing the preflare coronal magnetic field can significantly affect flare energetics and observable signatures and suggest that non-force-free extrapolations provide a promising pathway toward more realistic data-constrained flare modelling.

• Veronig, Astrid M.; Dissauer, Karin; Kliem, Bernhard; Downs, Cooper; Hudson, Hugh S. & Jin, Meng [Vis alle 13 forfattere av denne artikkelen] (2025). Coronal dimmings and what they tell us about solar and stellar coronal mass ejections. Living Reviews in Solar Physics. 22(1). doi: 10.1007/s41116-025-00041-4. Fulltekst i vitenarkiv Vis sammendrag

  Coronal dimmings associated with coronal mass ejections (CMEs) from the Sun have gained much attention since the late 1990s when they were first observed in high-cadence imagery of the SOHO/EIT and Yohkoh/SXT instruments. They appear as localized sudden decreases of the coronal emission at extreme ultraviolet (EUV) and soft X-ray (SXR) wavelengths, that evolve impulsively during the lift-off and early expansion phase of a CME. Coronal dimmings have been interpreted as “footprints” of the erupting flux rope and also as indicators of the coronal mass loss by CMEs. However, these are only some aspects of coronal dimmings and how they relate to the overall CME/flare process. The goal of this review is to summarize our current understanding and observational findings on coronal dimmings, how they relate to CME simulations, and to discuss how they can be used to provide us with a deeper insight and diagnostics of the triggering of CMEs, the magnetic connectivities and coronal reconfigurations due to the CME as well as the replenishment of the corona after an eruption. In addition, we go beyond a pure review by introducing a new, physics-driven categorization of coronal dimmings based on the magnetic flux systems involved in the eruption process. Finally, we discuss the recent progress in studying coronal dimmings on solar-like and late-type stars, and how to use them as a diagnostics for stellar coronal mass ejections and their properties.

• Bhatnagar, Aditi; Prasad, Avijeet; Siverio, Daniel Elias Nóbrega; Voort, Luc Rouppe van der & Joshi, Jayant (2025). Small-scale dynamic phenomena associated with interacting fan-spine topologies: Quiet-Sun Ellerman bombs, UV brightenings, and chromospheric inverted-Y-shaped jets. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 698. doi: 10.1051/0004-6361/202453344. Fulltekst i vitenarkiv Vis sammendrag

  Context. Quiet-Sun Ellerman bombs (QSEBs) are small-scale magnetic reconnection events in the lower solar atmosphere. Sometimes, they exhibit transition region counterparts, known as ultraviolet (UV) brightenings. Magnetic field extrapolations suggest that QSEBs can occur at various locations of a fan-spine topology, with UV brightening occurring at the magnetic null point through a common reconnection process. Aims. We aim to understand how more complex magnetic field configurations such as interacting fan-spine topologies can cause small-scale dynamic phenomena in the lower atmosphere. Methods. QSEBs were detected using k -means clustering on H β observations from the Swedish 1-m Solar Telescope (SST). Further, chromospheric inverted-Y-shaped jets were identified in the H β blue wing. Magnetic field topologies were determined through potential field extrapolations from photospheric magnetograms derived from spectro-polarimetric observations in the Fe  I 6173 Å line. UV brightenings were detected in IRIS 1400 Å slit-jaw images. Results. We identify two distinct magnetic configurations associated with QSEBs, UV brightenings, and chromospheric inverted-Y-shaped jets. The first involves a nested fan-spine structure where, due to flux emergence, an inner 3D null forms inside the fan surface of an outer 3D null with some overlap. The QSEBs occur at two footpoints along the shared fan surface, with the UV brightening located near the outer 3D null point. The jet originates close to the two QSEBs and follows the path of high squashing factor, Q . We discuss a comparable scenario using a 2D numerical experiment with the Bifrost code. In the second case, two adjacent fan-spine topologies share fan footpoints at a common positive polarity patch, with the QSEB, along with a chromospheric inverted-Y-shaped jet, occurring at the intersection having high Q values. The width of the jets in our examples is about 0 . 3, and the height varies between 1–2. The width of the cusp measures between 1–2. Conclusions. This study demonstrates through observational and modelling support that small-scale dynamic phenomena, such as associated QSEBs, UV brightenings, and chromospheric inverted-Y-shaped jets, share a common origin driven by magnetic reconnection between interacting fan-spine topologies.

• Bhatnagar, Aditi; Prasad, Avijeet; Voort, Luc Rouppe van der; Siverio, Daniel Elias Nóbrega & Joshi, Jayant (2025). Magnetic topology of quiet-Sun Ellerman bombs and associated ultraviolet brightenings. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 693. doi: 10.1051/0004-6361/202452822. Fulltekst i vitenarkiv Vis sammendrag

  Context. Quiet-Sun Ellerman bombs (QSEBs) are small-scale magnetic reconnection events in the lower atmosphere of the quiet Sun. Recent work has shown that a small percentage of them can occur co-spatially and co-temporally with ultraviolet (UV) brightenings in the transition region. Aims. We aim to understand how the magnetic topologies associated with closely occurring QSEBs and UV brightenings can facilitate energy transport and connect these events. Methods. We used high-resolution Hβ observations from the Swedish 1-m Solar Telescope (SST) and detected QSEBs using k-means clustering. We obtained the magnetic field topology from potential field extrapolations using spectro-polarimetric data in the photospheric Fe I 6173 Å line. To detect UV brightenings, we used coordinated and co-aligned data from the Interface Region Imaging Spectrograph (IRIS) and imposed a threshold of 5σ above the median background on the (IRIS) 1400 Å slit-jaw image channel. Results. We identify four distinct magnetic configurations that associate QSEBs with UV brightenings, including a simple dipole configuration and more complex fan-spine topologies with a 3D magnetic null point. In the fan-spine topology, the UV brightenings occur near the 3D null point, while QSEBs can be found close to the footpoints of the outer spine, the inner spine, and the fan surface. The height of the 3D null varies between 0.2 Mm and 2.6 Mm, depending on the magnetic field strength in the region. Some QSEBs and UV brightenings, though occurring close to each other, are not topologically connected with the same reconnection process. The energy released during QSEBs falls in the range 1023–1024 ergs. Conclusions. This study shows that magnetic connectivity and topological features, such as 3D null points, are crucial in linking QSEBs in the lower atmosphere with UV brightenings in the transition region.

• Kumar, Sanjay; Kumar, Pawan; Sadashiv, .; Nayak, Sushree S.; Agarwal, Satyam & Prasad, Avijeet [Vis alle 8 forfattere av denne artikkelen] (2025). Data-Constrained Magnetohydrodynamics Simulation of a Confined X-Class Flare in NOAA Active Region 11166. Solar Physics. ISSN 0038-0938. 300(2). doi: 10.1007/s11207-025-02426-y. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Beck, C.; Prasad, Avijeet; Hu, Q.; Yalim, M.S.; Gosain, S. & Choudhary, D. Prasad (2025). Derivation and Application of a Scaling between Hinode/SP and SDO/HMI Vector Magnetic Fields to Improve Magnetic Field Extrapolations. The Astrophysical Journal (ApJ). ISSN 0004-637X. 978(2). doi: 10.3847/1538-4357/ad98e6. Fulltekst i vitenarkiv Vis sammendrag

  Full-disk measurements of the solar magnetic field by the Helioseismic and Magnetic Imager (HMI) are often used for magnetic field extrapolations, but its limited spatial and spectral resolution can lead to significant errors. We compare HMI data with observations of NOAA 12104 by the Hinode Spectropolarimeter (SP) to derive a scaling curve for the magnetic field strength, B. The SP data in the Fe i lines at 630 nm were inverted with the SIR code. We find that the Milne–Eddington inversion of HMI underestimates B and the line-of-sight flux, Φ, in all granulation surroundings by an average factor of 4.5 in plage and 9.2 in the quiet Sun in comparison to the SP. The deviation is inversely proportional to the magnetic fill factor, f, in the SP results. We derived a correction curve to match the HMI B with the effective flux B f in the SP data that scaled HMI B up by 1.3 on average. A comparison of non-force-free field extrapolations over a larger field of view without and with the correction revealed minor changes in connectivity and a proportional scaling of electric currents and Lorentz force (∝B ∼ 1.3) and free energy (∝B2 ∼ 2). Magnetic field extrapolations of HMI vector data with large areas of plage and quiet Sun will underestimate the photospheric magnetic field strength by a factor of 5–10 and the coronal magnetic flux by at least a factor of 2. An HMI inversion including a fill factor would mitigate the problem.

• Sen, Samrat; Prasad, Avijeet; Liakh, Valeriia & Keppens, Rony (2024). From eruption to post-flare rain: A 2.5D MHD model. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 688. doi: 10.1051/0004-6361/202449767. Fulltekst i vitenarkiv Vis sammendrag

  Context. Erupting magnetic flux ropes play an important role in producing solar flares, whereas fine-scale condensed coronal rain is often found in post-flare loops. However, the formation of the MFRs in the pre-flare stage and how this leads to coronal rain in a post-eruption magnetic loop is not fully understood. Aims. We explore the formation and eruption of MFRs, followed by the appearance of coronal rain in the post-flare loops to understand the magnetic and thermodynamic properties of eruptive events and their multi-thermal aspects in the solar atmosphere. Methods. We performed a resistive-magnetohydrodynamic simulation with the open-source code MPI-AMRVAC to explore the evolution of sheared magnetic arcades that can lead to flux rope eruptions. The system was in mechanical imbalance at the initial state and evolved self-consistently in a nonadiabatic atmosphere under the influence of radiative losses, thermal conduction, and background heating. We used an additional level of adaptive mesh refinement to achieve the smallest cell size of ≈32.7 km in each direction to reveal the fine structures in the system. Results. The system achieves a semi-equilibrium state after a short transient evolution from its initial mechanically imbalanced condition. A series of erupting MFRs is formed due to spontaneous magnetic reconnection across current sheets that are created underneath the erupting flux ropes. A gradual development of thermal imbalance is noted at a loop top in the post-eruption phase, which leads to catastrophic cooling and to the formation of condensations. We obtain plasma blobs that fall down along the magnetic loop in the form of coronal rain. The dynamical and thermodynamic properties of these cool condensations agree well with observations of post-flare coronal rain. Conclusions. Our simulation supports the development and eruption of multiple MFRs and the formation of coronal rain in post-flare loops. This is one of the key aspects required to reveal the mystery of coronal heating in the solar atmosphere.

• Yalim, M.S.; Frisse, M.; Beck, C.; Choudhary, D.P.; Prasad, Avijeet & Nayak, S.S. [Vis alle 7 forfattere av denne artikkelen] (2024). A Data-constrained Analysis for Joule Heating as a Solar Active Region Atmosphere Heating Mechanism. I. Sunspot Umbral Light Bridge. The Astrophysical Journal (ApJ). ISSN 0004-637X. 973(1). doi: 10.3847/1538-4357/ad5e75. Fulltekst i vitenarkiv
• Joshi, Reetika; Voort, Luc Rouppe van der; Schmieder, Birgitte; Moreno-Insertis, Fernando; Prasad, Avijeet & Aulanier, Guillaume [Vis alle 7 forfattere av denne artikkelen] (2024). High-resolution observations of recurrent jets from an arch filament system. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 691. doi: 10.1051/0004-6361/202449715. Fulltekst i vitenarkiv Vis sammendrag

  Context. Solar jets are collimated plasma ejections along magnetic field lines observed in hot (extreme-ultraviolet (EUV) jets) and cool (chromospheric surges) temperature diagnostics. Their trigger mechanisms and the relationship between hot and cool jets are still not completely understood. Aims. We aim to investigate the generation of a sequence of active-region solar jets and their evolution from the photospheric to the coronal heights using multithermal observations from ground-based and space-borne instruments. Methods. Using the synergy of high-spatial-resolution and high-temporal-resolution observations by the Swedish 1-m Solar Telescope (SST), along with the Solar Dynamics Observatory (SDO), we analyzed a sequence of solar jets originating in a mixed-polarity region between the leading and following sunspots of an active region. We investigated the kinematics of these jets using the spectra from the SST observations. We used a non-force-free field (NFFF) extrapolation technique to derive the magnetic field topology of the active region. Results. A mixed-polarity region is formed over a long period (24 hours) with persistent magnetic flux emergence. This region has been observed as an arch filament system (AFS) in chromospheric SST observations. In this region, negative polarities surrounded by positive polarities create a fan surface with a null point at a height of 6 Mm detected in the NFFF extrapolation. SST observations in the Hβ spectral line reveal a large flux rope over the AFS moving from north to south, causing successive EUV and cool jets to move in the east–west direction and later towards the south along the long open loops. Conclusions. The high-resolution SST observations (0.038 per pixel) resolve the dark area observed at the jet base and reveal the existence of an AFS with an extended cool jet, which may be the result of a peeling-like mechanism of the AFS. Based on the combined analysis of SST and AIA observations along with extrapolated magnetic topology, it is suggested that the magnetic reconnection site may move southward by approximately 20 Mm until it reaches a region where the open magnetic field lines are oriented north–south.

• Yalim, Mehmet Sarp; Zank, Gary; Beck, Christian; Choudhary, Debi Prasad; Prasad, Avijeet & Hu, Qiang [Vis alle 7 forfattere av denne artikkelen] (2023). Understanding the heating mechanism of the solar active region atmosphere in chromosphere. Journal of Physics: Conference Series (JPCS). ISSN 1742-6588. 2544(1). doi: 10.1088/1742-6596/2544/1/012006. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Understanding the mechanisms underlying the heating of the solar atmosphere is a fundamental problem in solar physics. In this paper, we present an overview of our research on understanding the heating mechanism of the solar active region atmosphere in chromosphere. We investigate Joule heating due to the dissipation of currents perpendicular to the magnetic field by the Cowling resistivity using a data-constrained analysis based on observational and tabulated theoretical/semi-empirical solar atmosphere model data. As target region, we focus on a sunspot umbral light bridge where we find that this heating mechanism plays an important role and is also highly dynamic.

• Prasad, Avijeet; Kumar, S.; Sterling, A.C.; Moore, R.L.; Aulanier, Guillaume & Bhattacharyya, R. [Vis alle 7 forfattere av denne artikkelen] (2023). Formation of an observed eruptive flux rope above the torus instability threshold through tether-cutting magnetic reconnection. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 677, s. A43–A43. doi: 10.1051/0004-6361/202346267. Fulltekst i vitenarkiv Vis sammendrag

  Context. Erupting magnetic flux ropes (MFRs) are believed to play a crucial role in producing solar flares. However, the formation of erupting MFRs in complex coronal magnetic configurations and the role of their subsequent evolution in the flaring events are not fully understood. Aims. We perform a magnetohydrodynamic (MHD) simulation of active region NOAA 12241 to understand the formation of a rising magnetic flux rope during the onset of an M6.9 flare on 2014 December 18 around 21:41 UT (SOL2014-12- 18T21:41M6.9), which was followed by the appearance of parallel flare ribbons. Methods. The MHD simulation was initialised with an extrapolated non-force-free magnetic field generated from the photospheric vector magnetogram of the active region taken a few minutes before the flare. Results. The initial magnetic field topology displays a pre-existing sheared arcade enveloping the polarity inversion line. The simulated dynamics exhibit the movement of the oppositely directed legs of the sheared arcade field lines towards each other due to the converging Lorentz force, resulting in the onset of tether-cutting magnetic reconnection that produces an underlying flare arcade and flare ribbons. Concurrently, a magnetic flux rope above the flare arcade develops inside the sheared arcade and shows a rising motion. The flux rope is found to be formed in a torus-unstable region, thereby explaining its eruptive nature. Interestingly, the location and rise of the rope are in good agreement with the corresponding observations seen in extreme-ultraviolet channels of the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO). Furthermore, the foot points of the simulation’s flare arcade match well with the location of the observed parallel ribbons of the flare. Conclusions. The presented simulation supports the development of the MFR by the tether-cutting magnetic reconnection inside the sheared coronal arcade during flare onset. The MFR is then found to extend along the polarity inversion line (PIL) through slip-running reconnection. The MFR’s eruptive nature is ascribed both to its formation in the torus-unstable region and also to the runaway tether-cutting reconnection.

• He, Wen; Jing, Ju; Wang, Haimin; Nayak, Sushree S. & Prasad, Avijeet (2023). Coronal Magnetic Field Extrapolation and Topological Analysis of Fine-scale Structures during Solar Flare Precursors. The Astrophysical Journal (ApJ). ISSN 0004-637X. 958(1). doi: 10.3847/1538-4357/ad0236. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Magnetic field plays an important role in various solar eruption phenomena. The formation and evolution of the characteristic magnetic field topology in solar eruptions are critical problems that will ultimately help us understand the origin of these eruptions in the solar source regions. With the development of advanced techniques and instruments, observations with higher resolutions in different wavelengths and fields of view have provided more quantitative information for finer structures. It is therefore essential to improve the method with which we study the magnetic field topology in the solar source regions by taking advantage of high-resolution observations. In this study, we employ a nonlinear force-free field extrapolation method based on a nonuniform grid setting for an M-class flare eruption event (SOL2015-06-22T17:39) with embedded vector magnetograms from the Solar Dynamics Observatory (SDO) and the Goode Solar Telescope (GST). The extrapolation results for which the nonuniform embedded magnetogram for the bottom boundary was employed are obtained by maintaining the native resolutions of the corresponding GST and SDO magnetograms. We compare the field line connectivity with the simultaneous GST/H α and SDO/Atmospheric Imaging Assembly observations for these fine-scale structures, which are associated with precursor brightenings. Then we perform a topological analysis of the field line connectivity corresponding to fine-scale magnetic field structures based on the extrapolation results. The analysis results indicate that when we combine the high-resolution GST magnetogram with a larger magnetogram from the SDO, the derived magnetic field topology is consistent with a scenario of magnetic reconnection among sheared field lines across the main polarity inversion line during solar flare precursors.

• Kumar, Sanjay; Prasad, Avijeet; Nayak, Sushree S.; Agarwal, Satyam & Bhattacharyya, R. (2023). Magnetohydrodynamics simulation of magnetic flux rope formation in a quadrupolar magnetic field configuration. Plasma Physics and Controlled Fusion. ISSN 0741-3335. 65(8). doi: 10.1088/1361-6587/acdd1d. Fulltekst i vitenarkiv
• Sahu, Suraj; Joshi, Bhuwan; Prasad, Avijeet & Cho, Kyung-Suk (2023). Evolution of Magnetic Fields and Energy Release Processes during Homologous Eruptive Flares. The Astrophysical Journal (ApJ). ISSN 0004-637X. 943(2). doi: 10.3847/1538-4357/acac2d. Fulltekst i vitenarkiv Vis sammendrag

  Abstract We explore the processes of the repetitive buildup and the explosive release of magnetic energy, together with the formation of magnetic flux ropes, which eventually resulted in three homologous eruptive flares of successively increasing intensities (i.e., M2.0, M2.6, and X1.0). The flares originated from NOAA active region 12017 between 2014 March 28 and 29. EUV observations and magnetogram measurements, together with coronal magnetic field modeling, suggest that the flares were triggered by the eruption of flux ropes that were embedded in a densely packed system of loops within a small part of the active region. In X-rays, the first and second events show similar evolutions, with single compact sources, while the third event exhibits multiple emission centroids, with a set of strong nonthermal conjugate sources at 50–100 keV during the hard X-ray peak. Over an interval of ≈ 44 hr, the photospheric magnetic field encompassing the three flares undergoes important phases of emergence and cancellation, together with significant changes near the polarity inversion lines within the flaring region. Our observations point toward the tether-cutting mechanism being the plausible triggering process of the eruptions. Between the second and third events, we observe a prominent phase of flux emergence that temporally correlates with the buildup phase of free magnetic energy in the active region corona. In conclusion, our analysis reveals efficient coupling between the rapidly evolving photospheric and coronal magnetic fields in the active region, leading to a continued phase of the buildup of free energy, which results in the homologous flares of successively increasing intensities.

• Hu, Qiang; Zhu, Chunming; He, Wen; Qiu, Jiong; Jian, Lan K. & Prasad, Avijeet (2022). Validation and Interpretation of a Three-dimensional Configuration of a Magnetic Cloud Flux Rope. The Astrophysical Journal (ApJ). ISSN 0004-637X. 934(1). doi: 10.3847/1538-4357/ac7803. Fulltekst i vitenarkiv Vis sammendrag

  Abstract One strong magnetic cloud (MC) with a magnetic field magnitude reaching ∼40 nT at 1 au during 2012 June 16–17 is examined in association with a preexisting magnetic flux rope (MFR) identified on the Sun. The MC is characterized by a quasi-three-dimensional (3D) flux rope model based on in situ measurements from the Wind spacecraft. The contents of the magnetic flux and other parameters are quantified. In addition, a correlative study with the corresponding measurements of the same structure crossed by the Venus Express (VEX) spacecraft at a heliocentric distance of 0.7 au and with an angular separation of ∼6° in longitude is performed to validate the MC modeling results. The spatial variation between the Wind and VEX magnetic field measurements is attributed to the 3D configuration of the structure appearing as a knotted bundle of flux. A comparison of the magnetic flux contents between the MC and the preexisting MFR on the Sun indicates that the 3D reconnection process accompanying an M1.9 flare may correspond to the magnetic reconnection between the field lines of the preexisting MFR rooted in the opposite polarity footpoints. Such a process reduces the amount of the axial magnetic flux in the erupted flux rope, by approximately 50%, in this case.

• Prasad, Avijeet; Ranganathan, M.; Beck, C.; Choudhary, D.P. & Hu, Q. (2022). The magnetic topology of the inverse Evershed flow. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 662. doi: 10.1051/0004-6361/202142585. Fulltekst i vitenarkiv
• Kumar, Sanjay; Prasad, Avijeet; Sarkar, Ranadeep & Bhattacharyya, Ramit (2022). Magnetohydrodynamics evolution of three-dimensional magnetic null in NOAA active region 11515 initiated using non-force-free field extrapolation. Frontiers in Astronomy and Space Sciences. 9. doi: 10.3389/fspas.2022.1039061. Fulltekst i vitenarkiv Vis sammendrag

  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 2 July 2012. 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.

• Bora, Kamelesh; Bhattacharyya, R.; Prasad, Avijeet; Joshi, Bhuwan & Hu, Qiang (2022). Comparison of the Hall Magnetohydrodynamics and Magnetohydrodynamics Evolution of a Flaring Solar Active Region. The Astrophysical Journal (ApJ). ISSN 0004-637X. 925(2). doi: 10.3847/1538-4357/ac3bce. Fulltekst i vitenarkiv Vis sammendrag

  This work analyzes the Hall magnetohydrodynamics (HMHD) and magnetohydrodynamics (MHD) numerical simulations of a flaring solar active region as a test bed while idealizing the coronal Alfvén speed to be less by two orders of magnitude. 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 multiwavelength 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 ascent of the rope together with the overlying field lines, which further reconnect at the QSL located higher up in the corona. The footpoints 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 cospatial 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.

• He, Wen; Hu, Qiang; Jiang, Chaowei; Qiu, Jiong & Prasad, Avijeet (2022). Quantitative Characterization of Magnetic Flux Rope Properties for Two Solar Eruption Events. The Astrophysical Journal (ApJ). ISSN 0004-637X. 934(2). doi: 10.3847/1538-4357/ac78df. Fulltekst i vitenarkiv Vis sammendrag

  In order to bridge the gap between heliospheric and solar observations of coronal mass ejections (CMEs), one of the key steps is to improve the understanding of their corresponding magnetic structures like the magnetic flux ropes (MFRs). But it remains a challenge to confirm the existence of a coherent MFR before or upon the CME eruption on the Sun and to quantitatively characterize the CME-MFR due to the lack of direct magnetic field measurements in the corona. In this study, we investigate MFR structures originating from two active regions (ARs), AR 11719 and AR 12158, and estimate their magnetic properties quantitatively. We perform nonlinear force-free field extrapolations with preprocessed photospheric vector magnetograms. In addition, remote-sensing observations are employed to find indirect evidence of MFRs on the Sun and to analyze the time evolution of magnetic reconnection flux associated with the flare ribbons during the eruption. A coherent "preexisting" MFR structure prior to the flare eruption is identified quantitatively for one event from the combined analysis of the extrapolation and observation. Then the characteristics of MFRs for two events on the Sun before and during the eruption forming the CME-MFR, including the axial magnetic flux, field line twist, and reconnection flux, are estimated and compared with the corresponding in situ modeling results. We find that the magnetic reconnection associated with the accompanying flares for both events injects a significant amount of flux into the erupted CME-MFRs.

Se alle arbeider i NVA

• Prasad, Avijeet (2024). Towards Data-Constrained Radiative-Magnetohydrodynamics Simulations of the Solar Atmosphere using the Bifrost Code. Fulltekst i vitenarkiv
• Prasad, Avijeet (2023). Data-constrained magnetohydrodynamics simulations of the solar atmosphere using the Bifrost code. Fulltekst i vitenarkiv
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• Prasad, Avijeet (2022). Inferring the magnetic topology of the inverse Evershed flow using non-force-free extrapolations. Fulltekst i vitenarkiv
• Prasad, Avijeet (2022). MHD modelling of eruptive phenomena in the solar atmosphere. Fulltekst i vitenarkiv
• Prasad, Avijeet (2021). An investigation of the magnetic topology of the inverse Evershed flow. Fulltekst i vitenarkiv
• Prasad, Avijeet (2021). MHD simulations of the solar corona initiated with non-force-free fields. Fulltekst i vitenarkiv

Se alle arbeider i NVA