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.

💡 Research Summary

This paper presents a comprehensive investigation of a C1.1 flare and an associated blow‑out jet that occurred on 10 November 2022 in active region (AR) SPoCA 29093. The authors combine multi‑wavelength observations from SDO/AIA (131 Å, 171 Å, 193 Å, 304 Å), GOES soft X‑ray flux, and vector magnetograms from SDO/HMI with a data‑constrained three‑dimensional magnetohydrodynamic (MHD) simulation. The observational analysis shows that the flare began at ≈ 03:09 UT, peaked at 03:12 UT, and was followed by a blow‑out jet that fully developed by ≈ 03:18 UT. Throughout the ≈ 30‑minute interval surrounding the event, the total positive and negative line‑of‑sight magnetic flux in the region varied by less than 1 %, indicating that flux emergence was not the primary driver.

To reconstruct the coronal magnetic field, the authors employ a non‑force‑free‑field (NFFF) extrapolation based on the double‑curl Beltrami formulation. This method decomposes the field into three linear force‑free components, iteratively adjusting the force‑free parameters (α₁ = α₃, α₂ = 0) to minimize the discrepancy between the observed transverse field and the model. Convergence is achieved after 4000 iterations, yielding a field in which the Lorentz force is negligible above the low chromosphere, as expected for coronal conditions.

The extrapolated topology reveals a three‑dimensional magnetic null point located at a height of ≈ 7.3 Mm, surrounded by a dome‑shaped fan surface and spine lines. The lower spine is rooted in a positive polarity patch, while the upper spine is open (or connects to distant positive flux). Embedded beneath the fan is a twisted magnetic flux rope (MFR) with a twist number of about –1.2, consistent with the observed rotational motion of the jet.

Using the EULAG‑MHD code, the authors initialize a full‑3D MHD simulation with the NFFF field as the initial condition and an isothermal, low‑β atmosphere. The simulation captures the gradual rise of the MFR, its interaction with the fan‑spine structure, and the formation of a thin current sheet at the null. Crucially, the model exhibits spontaneous creation of a pair of three‑dimensional null points, followed shortly by their annihilation. This null‑pair dynamics concentrates electric currents and drives rapid reconnection. The reconnection simultaneously releases magnetic energy (producing the observed soft‑X‑ray flare) and accelerates plasma along the open spine, generating the blow‑out jet. The timing of these processes matches the observations: the flare and jet onset occur within roughly one minute of each other.

The study therefore identifies two key ingredients for the observed event: (1) the coexistence of a 3D null and an underlying flux rope, providing a pre‑existing magnetic configuration capable of storing free energy, and (2) the dynamic generation and removal of null‑point pairs, which act as a catalyst for fast reconnection. While previous blow‑out jet models (e.g., magnetic breakout) emphasized flux‑rope eruption and breakout reconnection, this work adds the novel mechanism of null‑pair creation as an additional trigger.

In the discussion, the authors argue that null‑pair generation could be a generic feature of complex active‑region topologies, offering a pathway for rapid energy release without the need for large‑scale flux emergence or shear flows. They suggest that future observational campaigns should target signatures of null‑pair dynamics (e.g., localized brightening, rapid changes in connectivity) and that data‑constrained MHD simulations, like the one presented, are essential for linking magnetic topology to eruptive phenomena.

Overall, the paper advances our understanding of how three‑dimensional magnetic structures in active regions can produce simultaneous flare and jet eruptions, highlighting the importance of magnetic null points and their dynamic behavior in solar eruptive physics.