A self-consistent 3D MHD model producing a solar blowout jet

Context. Solar blowout jets are a distinct subclass of ubiquitous extreme-ultraviolet (EUV) and X-ray coronal jets. Aims. Most existing models of blowout jets prescribe an initial magnetic field configurations and apply ad-hoc changes in the photosphere to trigger the jets. In contrast, we aim for a self-consistent magneto-convective description of the jet initiation. Methods. We employ a 3D radiation magnetohydrodynamic (MHD) model of a solar coronal hole region using the MURaM code. The computational domain extends from the upper convection zone to the lower corona. We synthesize the emission in the extreme UV and X-rays for a direct comparison to observations and examine the evolution of the magnetic field structure of the event. Results. In the simulation a twisted flux tube forms self-consistently, emerges through the surface and interacts with the pre-existing open field. Initially the resulting jet is of the standard type with a narrow spire. The release of the twist into the open field causes a broadening of the jet spire turning the jet into a blowout type. At the same time this creates a fast heating front propagating at the local Alfvén speed. The properties of the modeled jet closely match observations of blowout jets: a slow (180 km/s) mass upflow and a fast (500 km/s) propagating front form, the latter being a signature of the heating front. Also the timing of the jet with respect to the flux emergence and subsequent cancellation matches observations. Conclusions. The near-surface magneto-convection self-consistently generates a twisted flux tube that emerges through the photosphere. The tube then interacts with the pre-existing magnetic field by means of interchange reconnection. This transfers the twist to the open field region and produces a blowout jet that matches the main characteristics of this type of jet found in observations.

💡 Research Summary

Solar blowout jets are a distinct subclass of coronal jets characterized by a rapid widening of the spire, untwisting helical motions, and the presence of both a bulk mass flow (≈200 km s⁻¹) and a much faster component (≈700 km s⁻¹) that is generally interpreted as an Alfvénic heating front. Most previous numerical studies have prescribed a pre‑existing twisted flux rope or imposed artificial photospheric motions to trigger reconnection, thereby limiting the realism of the jet initiation process.

In this work the authors employ the state‑of‑the‑art MURaM radiation magnetohydrodynamic code to simulate a coronal‑hole region from the upper convection zone (≈‑20 Mm) through the photosphere, transition region and into a low corona extending to 30 Mm. The computational box spans 54 × 54 Mm horizontally with a uniform grid spacing of ~52.7 km and a vertical resolution of 20 km. Apart from adding a modest uniform vertical field of 5 G to mimic the open flux of a coronal hole, no magnetic structures are imposed; the system is driven solely by a small‑scale dynamo that naturally generates magnetic fields.

During a ten‑hour run a twisted magnetic flux tube forms spontaneously in the convection zone, rises, and emerges through the photosphere. The emergence is accompanied by the appearance of mixed‑polarity patches that separate over several megameters and subsequently cancel. This evolution creates a configuration in which the newly emerged closed loops interact with the pre‑existing open field via interchange reconnection. The reconnection transfers magnetic twist from the emerging tube to the ambient open field.

Initially the reconnection produces a narrow, standard‑type jet spire. As twist is continuously injected into the open field, the spire widens dramatically, converting the event into a blowout jet. Synthetic observations are generated for three passbands: AIA 304 Å (≈10⁵ K), Solar Orbiter EUI 174 Å (≈10⁶ K), and Hinode XRT Al‑poly (≈2 × 10⁶ K). The jet is clearly visible in all channels; the 304 Å emission highlights a cool core, consistent with observations of blowout jets that often show strong chromospheric/transition‑region signatures.

Space‑time diagrams constructed from artificial slits placed at several heights reveal two distinct propagation speeds. In the 174 Å channel the bulk upward motion is ≈184 km s⁻¹, matching the typical mass‑flow component reported in observations. In the XRT channel a much faster apparent motion of ≈504 km s⁻¹ is seen. Direct analysis of the plasma velocity field shows that actual flow speeds never exceed ~400 km s⁻¹, indicating that the fast XRT signal is not a bulk flow. By examining the summed Joule and viscous heating rates, the authors identify an upward‑propagating heating front moving at the same ≈500 km s⁻¹ speed. This front, traveling at the local Alfvén speed, accounts for the high‑speed component observed in hot channels and provides a natural explanation for the dual‑speed signatures of blowout jets.

The magnetic flux analysis shows that the total unsigned flux in the region beneath the jet increases during emergence, reaches a maximum, and then declines as cancellation proceeds. The timing between the flux peak and the jet onset is about ten minutes, reflecting the time required for the emerged field to rise to coronal heights and form a reconnection‑prone topology. The magnitude of flux change (~0.5 × 10¹⁹ Mx) is comparable to values measured in observational case studies.

Overall, the study demonstrates that a self‑consistent magneto‑convective process can generate all essential ingredients of a blowout jet—flux emergence, interchange reconnection, twist transfer, spire widening, untwisting motions, and a propagating heating front—without any ad‑hoc magnetic setup. The simulated jet reproduces key observational diagnostics (morphology, multi‑thermal emission, dual speed components, and timing relative to flux evolution) and thus bridges the gap between idealized models and real solar behavior.

The authors acknowledge limitations: the vertical domain (30 Mm) does not capture the full propagation of the jet into the outer corona, and the optically thin assumption for the 304 Å channel is a simplification. Future work should extend the domain, incorporate full radiative transfer for chromospheric lines, and explore parameter variations (e.g., background field strength, dynamo efficiency) to assess the robustness of the blowout‑jet formation mechanism.