Ramit Bhattacharyya

Solar flares are intermittent events that convert free magnetic energy into heat and kinetic energy of charged particles, along with a rearrangement of magnetic field lines (MFLs) through magnetic reconnection. This work investigates an active-region sub-A-class microflare detected by the Solar X-ray Monitor on board Chandrayaan-2. The MFL topology, its evolution, and the associated magnetic reconnection in the flaring region are investigated. The coronal magnetic field is constructed using the nonlinear force-free field (NLFFF) extrapolation model, indicating the presence of a magnetic flux rope (MFR) at the flaring location. Notably, this MFR exhibits regions of high magnetic field gradient and a nonuniform distribution of twist along its axis. Furthermore, the dynamics of the MFR is explored using a three-dimensional data-constrained magnetohydrodynamics simulation performed using the EULAG-MHD code. The simulation shows overall untangling of the MFLs that constitute the MFR, along with changes in their connectivity, which suggests underlying magnetic reconnection. Further, a few representative MFLs belonging to the MFR over a given time span are advected with the plasma flow to maintain their identity. These field lines show a change in connectivity, and such reconnections can contribute to the unfurling of the MFR. The overall scenario is generally consistent with the concept of braiding reconnection in an MFR.

We present observations of and a magnetic reconnection scenario for a twin pair of “atypical flares” that occurred on 2022 April 22 in a quadrupolar magnetic configuration formed by two active regions. The spatiotemporal evolution of the two flares is examined using images from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory and from the ground-based Multi-Application Solar Telescope in Udaipur, India. Characteristic of atypical flares and indicative of slipping reconnection, the ribbons of each of our atypical flares: (1) do not spread apart; and (2) grow longer by the 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 releasing much less energy than the atypical flares. Two of these four pairs are each made by a precursor, each possibly triggering one of the two atypical flares. The remaining two pairs accompany a filament’s activation, occurring twice within the span of the two atypical flares. Using a nonlinear force-free-field extrapolation model, we approximate the coronal magnetic field and find two quasi-separatrix layers (QSLs) that are nearly rooted in the flare ribbons of the atypical flares. The observations and the extrapolated field together suggest a scenario in which the nearly simultaneous occurrence of many reconnections between magnetic field lines crossing each other at small angles (slipping reconnection) within each of the two QSLs makes the observed pair of atypical flares.

Solar flares are sudden, explosive events on the Sun in which magnetic energy, ranging from 10 ²³ to 10 ³² erg, is released in the form of heat and acceleration of charged particles, along with a rearrangement of magnetic field lines by magnetic reconnection. Energetically large flares affect the near-Earth space weather and have been extensively studied. In contrast, microflares and nanoflares are relatively less explored, since their detection requires more sensitive observations. However, a systematic and holistic study of these flares can contribute to the physics of small-scale energy release events and to their role in research problems related to both chromospheric and coronal heating. Consequently, this paper investigates magnetic reconnection in a Geostationary Operational Environmental Satellite (GOES) B-class flare, loosely classified as a microflare, using multi-instrument data and 3D data-constrained magnetohydrodynamics (MHD) simulations. Light curves of the Solar X-ray Monitor (XSM) and GOES are compared, showing that preflare (phase-1) and impulsive phases (phase-2) of the flare are better resolved by XSM. Non-force-free field extrapolations of the host active region (AR12759) reveal two hyperbolic flux tubes (HFTs). To understand the reconnection details of phase 1 and phase 2, data-constrained MHD simulations are carried out using the extrapolated data as input to the MHD code—EULAG-MHD, identifying one of the HFTs as the reconnection site of the observed flare. Furthermore, a comparison of the two phases is made, suggesting a near similarity in terms of the reconnection mechanism and dynamics of reconnected field lines; however, details of energetics—particularly dissipation and the conversion of magnetic energy to kinetic energy—are different.

Coronal jets are collimated plasma eruptions that 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, is particularly interesting because of their broad spire, suggesting substantial 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 SPoCA 29093 detected by the Spatial Possibilistic Clustering Algorithm (SPoCA). This AR produced a C1.1-class flare on 2022 November 10, and we investigate it using a data-constrained magnetohydrodynamic simulation initiated with a non-force-free field 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) colocated 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 Atmospheric Imaging Assembly/Solar Dynamics Observatory. 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.

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.

Coronal jets are the captivating eruptions that are often found in the solar atmosphere and primarily formed due to magnetic reconnection. Despite their short-lived nature and lower energy compared to many other eruptive events, e.g., flares and coronal mass ejections, they play an important role in heating the corona and accelerating charged particles. However, their generation in the ambience of nonstandard flare regime is not fully understood, and warrant a deeper investigation, in terms of their onset, growth, eruption processes, and thermodynamic evolution. Toward this goal, this paper reports the results of a data-constrained three-dimensional magnetohydrodynamics (MHD) simulation of an eruptive jet; initialized with a non-force-free-field (NFFF) extrapolation and carried out in the spirit of implicit large eddy simulation (ILES). The simulation focuses on the magnetic and dynamical properties of the jet during its onset, and eruption phases, that occurred on 2015 February 5 in an active region NOAA AR12280, associated with a seemingly three-ribbon structure. In order to correlate its thermal evolution with computed energetics, the simulation results are compared with differential emission measurement analysis in the vicinity of the jet. Importantly, this combined approach provides an insight to the onset of reconnection in transients in terms of emission and the corresponding electric current profiles from MHD evolutions. The presented study captures the intricate topological dynamics, finds a close correspondence between the magnetic and thermal evolution in and around the jet location. Overall, it enriches the understanding of the thermal evolution due to MHD processes, which is one of the broader aspects to reveal the coronal heating problem.