Kumar et al. (2021) observed three intermediate-scale pseudostreamer eruptions spanning the 'breakout continuum' between coronal jets and coronal mass ejections (CMEs) and concluded that the decisive factor is the ratio of the magnetic free energy stored in the sheared filament channel to the magnetic energy of the overlying 'strapping' field (the closed flux rooted outside the filament channel plus the surrounding open flux). This criterion has never been quantitatively tested: no statistical sample of pseudostreamer eruptions has had the ratio measured from coronal magnetic fields, and the systematic numerical experiments varying the fluxes in the key zones — which the authors stated were being planned — had still not been carried out by the most recent follow-up work (Wyper et al. 2024 explicitly defers them to future simulations). The problem is to convert this hypothesis into a validated predictive criterion: measure or compute the energy ratio for a statistical sample of eruptions, map the parameter-space boundary between jets, hybrid events, and CMEs through targeted simulations, quantify the secondary role of eruption speed relative to the local Alfvén speed in flux-rope survival, and settle whether intensified coronal rain is a reliable precursor of breakout onset.

Background

A coronal mass ejection (CME) is the large-scale ejection of magnetized plasma and magnetic flux from the Sun's corona into interplanetary space, while a coronal jet is a much smaller, collimated transient produced by magnetic reconnection. The magnetic breakout model (Antiochos, DeVore & Klimchuk 1999) explains eruptions in multipolar magnetic configurations: energy builds up in a sheared 'filament channel' (the channel of strongly non-potential, low-lying field above a polarity inversion line that may host a filament), and reconnection at a current sheet above the channel removes the overlying restraining field, allowing the channel's flux to erupt. Numerical simulations (e.g. Wyper et al. 2018) and observations (e.g. Kumar et al. 2018) showed that the same breakout sequence operates in fan-spine topologies and produces coronal-hole jets, establishing breakout as a candidate universal eruption mechanism spanning jets and CMEs.

A pseudostreamer is a coronal structure consisting of a dome of closed magnetic loops enclosed by open field of a single magnetic polarity (unlike a helmet streamer, which separates open fields of opposite polarity); its boundary is a three-dimensional null point of the magnetic field, where the field vanishes and reconnection concentrates, forming a fan (the dome surface) and spine (the external open field line through the null). Kumar et al. (2021, ApJ, 907) analyzed three eruptions from intermediate-scale pseudostreamers — source regions deliberately chosen to be capable of producing either jets or CMEs — using extreme-ultraviolet imaging from the Atmospheric Imaging Assembly (AIA) on NASA's Solar Dynamics Observatory (SDO), white-light coronagraphy from the Large Angle and Spectrometric Coronagraph (LASCO) on the Solar and Heliospheric Observatory (SOHO), and hard X-ray data from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). They found two new pre-eruption signatures of slow breakout reconnection, coronal dimming (transient depletion of EUV emission where plasma drains or field opens) and the opening of field lines above the breakout current sheet, and they showed that source-region size, photospheric field strength, magnetic configuration, and pre-eruptive evolution did not discriminate between the jet and CME outcomes. They concluded that the controlling quantity is the ratio of the magnetic free energy (the energy above that of the corresponding potential, current-free field) in the sheared filament channel to the energy of the overlying 'strapping' field — the closed flux rooted outside the filament channel plus the open flux that bends over the separatrix dome. We denote this ratio by RR; the paper itself states the criterion in words. This is analogous in spirit to the decay-index criterion of the torus instability (Kliem & Török 2006), which predicts eruption from the rate at which confining field decreases with height, but the breakout energy-ratio criterion is specific to multipolar, null-point topologies and has never been calibrated.

The obstacle to testing the criterion is that the coronal magnetic field cannot yet be measured routinely: vector fields are measured only at the photospheric level on the solar disk, so the coronal field must be inferred from extrapolations that are poorly constrained, and computing the free energy of a filament channel additionally requires knowledge of the channel width and the transverse field within it, for which routine high-resolution chromospheric observations are lacking. The Daniel K. Inouye Solar Telescope (DKIST), a 4-meter ground-based solar telescope designed in part for coronal spectropolarimetry, was identified by the authors as the instrument that could measure coronal fields in and around erupting flux ropes. The filament channel erupts as a magnetic flux rope (a twisted bundle of field lines), and the authors argued that the outcome also depends on eruption speed: a rope moving at or above the local Alfvén speed (the characteristic propagation speed of magnetic disturbances in a magnetized plasma) can survive the interchange reconnection with the oppositely directed open flux beside the pseudostreamer stalk, whereas a slow rope is eroded before reaching the effective Alfvén point at roughly 10–20 solar radii. They also noted intensified coronal rain — cool plasma condensing and draining along loop-shaped field lines, a phenomenon of thermal non-equilibrium observed in null-point topologies by Mason et al. (2019) — coincident with pre-eruption dimming, and called for a dedicated statistical study of its predictive value.

Problem Statement

Establish, quantitatively, the criterion that determines whether an eruption from an intermediate-scale pseudostreamer produces a jet or a coronal mass ejection, as posed by Kumar et al. (2021). Denoting by RR the ratio of the magnetic free energy of the sheared filament channel to the magnetic energy of the overlying strapping field (the closed flux rooted outside the channel plus the open flux bending over the separatrix dome), the problem comprises four jointly linked parts serving one objective — converting the breakout-continuum hypothesis into a predictive capability for eruption outcome: (1) Test and calibrate the energy-ratio criterion observationally: for a statistically significant sample of pseudostreamer eruptions, determine the magnetic free energy of the filament channel and the energy of the overlying closed and open flux from direct coronal vector-field measurements or well-constrained extrapolations, compute RR for each event, classify the outcome (jet; hybrid, meaning an event showing both a collimated jet and a CME-like bubble; or narrow or broad CME) from EUV and coronagraph data, and establish whether a threshold in RR separates the outcomes and what its value and confidence bounds are. (2) Perform the targeted numerical experiments the authors stated were planned: starting from a fixed pseudostreamer configuration, systematically vary the fluxes in the three key zones (filament-channel core, overlying closed dome flux, surrounding open flux), quantify RR in each run, and determine the boundary in this parameter space separating jets, hybrid events, and CMEs, thereby confirming or refuting that RR — rather than, e.g., total flux content, the torus-instability decay index, or null-point height — is the controlling parameter. (3) Quantify the secondary condition for flux-rope survival: determine the role of the eruption speed relative to the local Alfvén speed, including the location of the effective Alfvén point and how interchange reconnection beyond it erodes or preserves the rope, using coupled coronal-heliospheric modeling and multi-height observations. (4) Establish statistically, from a dedicated survey of a large event sample, whether intensified coronal rain is a reliable precursor of breakout reconnection and eruption onset, and quantify its predictive utility if so. An answer that refutes the criterion — for example, a statistical sample or parameter survey in which RR fails to discriminate outcomes, with an analysis of which quantity does — is equally admissible, provided it is grounded in the same measured quantities. A solution must address parts (1) and (2); parts (3) and (4) are required in addition unless the RR criterion is refuted, in which case reporting the refutation, together with the quantity that does discriminate the outcomes, suffices.

References

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