Chen et al. (2021) stereoscopically observed a blowout coronal jet whose unwinding spire transported roughly 1.4–2.0 turns of magnetic twist through null-point reconnection into remote closed flux, rapidly creating a newborn large-scale magnetic flux rope that immediately erupted as an Earth-directed coronal mass ejection. The authors left two questions explicitly open: (1) whether this rapid twist-transport mechanism is a general formation pathway capable of producing long-lived, large-scale flux ropes among inter-coupled active regions — ropes that persist for hours to days along extended polarity inversion lines (the photospheric boundaries separating opposite magnetic polarities) — rather than only immediately eruptive ones formed at high coronal heights; and (2) how jet-base parameters (pre-jet filament twist, jet rotational speed, mass loading, injected magnetic helicity) quantitatively couple to the magnetic content, energetics, interplanetary propagation, and geoeffectiveness of the resulting CME. Neither question has been answered: no later study reports a long-lived inter-active-region flux rope formed by jet twist transport, a controlled determination of when twist transport yields a stable versus immediately eruptive rope, or a quantitative scaling from jet-base parameters to CME magnetic content and geoeffectiveness.

Background

Coronal mass ejections (CMEs) are large-scale expulsions of magnetized plasma from the Sun into interplanetary space and the main drivers of geomagnetic storms; their core magnetic structure is widely modeled as a magnetic flux rope (MFR) — a set of coherent, helically wound field lines winding around a common axis that stores magnetic free energy and helicity. Coronal jets, by contrast, are much smaller collimated plasma ejections, typically triggered when a small filament or minifilament erupts inside a fan-spine magnetic configuration; in the blowout-jet variant the filament material and its wrapped field actually escape, and the jet spire often shows an untwisting (rotational) motion as accumulated magnetic twist relaxes. Magnetic helicity is a measure of field-line linkage and twisting that is approximately conserved even under reconnection, so twist released by an unwinding jet must be carried elsewhere — this is the physical basis of twist transport between magnetic structures.

The two questions addressed here arose from a specific event. On 2012 July 2, in a multipolar system involving the inter-coupled active regions NOAA 11514 and 11515 (active regions whose magnetic fields are topologically connected so that activity in one disturbs the other), a small filament erupted at a recurrent jet-producing site after four homologous jets (recurrent, near-identical eruptions from the same source site). Interacting with an overlying null point — a location where the magnetic field vanishes and reconnection between different flux domains can occur, surrounded by a fan-spine topology in which field lines around the null form a dome-like fan surface beneath outward-extending spine field lines — the erupting filament broke one of its legs, producing an unwinding blowout jet whose spire released about 1.4–2.0 turns of twist. That twist was transported along the spire into remote closed loops, rapidly assembling a newborn flux rope spanning from the jet base to the remote site, which promptly erupted as an Earth-directed CME accompanied by two distinct sets of post-flare loops indicating two-stage flare reconnection. The interpretation rested on nonlinear force-free field (NLFFF) extrapolation, a standard technique that reconstructs the coronal magnetic field from photospheric vector magnetograms under the assumption that Lorentz forces vanish, and on field-line twist diagnostics computed from such reconstructions.

Whether small-scale jet reconnection can generally seed large-scale eruptive ropes matters because long-lived, large-scale MFRs anchored among inter-coupled active regions are known to exist and to produce major eruptions: Zhou et al. (2019) identified a hot-channel MFR (a flux rope seen in extreme-ultraviolet images as a hot, twisted, thread-like structure) connecting two active regions whose formation they explicitly flagged as unresolved, and Duan et al. (2021) tracked a five-day-lived inter-active-region MFR whose twist was built gradually by sunspot rotation and flux cancellation rather than by any jet. A closely analogous formation sequence — an erupting sigmoid whose leg breaks and gives birth to a highly twisted rope — was reproduced in the data-constrained 3D magnetohydrodynamic (MHD) simulation of Jiang et al. (2018), showing that such modeling is feasible, but no simulation has yet reproduced the jet-spire twist-transport route of the 2012 July 2 event. Related statistical work has clarified what jets do to CME morphology (Duan et al. 2024) and how large the helicity and energy budgets of jets are (Nindos et al. 2024), but the cross-scale coupling from jet-base parameters to CME magnetic content and geoeffectiveness — the practical measure of a CME's capacity to drive geomagnetic storms, usually quantified by the southward interplanetary magnetic field and the resulting disturbance storm time (Dst) index — remains unquantified.

Problem Statement

Establish whether the twist-transport formation channel observed by Chen et al. (2021) is a general pathway for building large-scale CME flux ropes, by answering the two linked questions the source explicitly poses:

  1. Generality and stability: determine whether the rapid twist-transport mechanism — an erupting filament whose broken leg reconnects at a null point with remote closed flux, so that the unwinding jet spire transports magnetic twist and assembles a newborn large-scale magnetic flux rope — can produce long-lived, large-scale MFRs among inter-coupled active regions (ropes that persist along extended polarity inversion lines — the photospheric boundaries separating opposite magnetic polarities — for hours to days before any eruption), given that the one directly observed case formed at relatively high coronal height and erupted immediately. This requires identifying the physical conditions — magnetic topology, reconnection rates, and formation height — under which twist transport yields a stable large-scale rope rather than an immediately eruptive one.

  2. Energetic coupling: quantify how jet-base parameters (pre-jet filament twist, jet rotational/unwinding speed, mass loading, injected magnetic helicity) scale with the magnetic content of the resulting CME — its flux, helicity, and free energy — and with its interplanetary propagation and geoeffectiveness.

The two questions jointly serve one objective: establishing the cross-scale magnetic coupling by which small-scale jet reconnection seeds large-scale eruptive flux ropes, as needed to fully understand jet–CME coupling eruption events. The two questions are jointly posed and both bear on that objective; for question 1 a general criterion over magnetic topology, reconnection rate, and formation height is required, not a single example.

References

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