🔭 astrophysics

Successive Coronal Jets as Novel Facilitators for Filament Oscillation and Eruption

This study combines multi-instrument observations and magnetohydrodynamic simulations to demonstrate that successive coronal jets can trigger filament eruptions by inducing growing oscillations that serve as observable precursors, ultimately driving the filament to instability when it reaches a critical height.

Original authors: Chengrui Zhou, Chun Xia, Wentai Fu, Hechao Chen, Qiaoling Li

Published 2026-07-10

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CC BY 4.0

Original authors: Chengrui Zhou, Chun Xia, Wentai Fu, Hechao Chen, Qiaoling Li

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the Sun's atmosphere as a giant, invisible trampoline made of magnetic fields. Sitting on this trampoline is a solar filament—a long, cool, dark ribbon of plasma that usually hangs out quite happily, suspended in the super-hot solar corona. But sometimes, these ribbons decide to jump, erupting into space and causing space weather storms that can mess with our satellites and power grids. The big mystery has always been: What makes them jump?

In this study, researchers acted like cosmic detectives, using a fleet of space telescopes (like SDO, STEREO, and Hinode) and ground-based super-cameras to watch a specific filament on February 23, 2019. They found a fascinating chain reaction: successive coronal jets (little bursts of solar wind) were hitting the filament like a series of nudges, causing it to wobble, rise, and eventually launch.

The "Nudge-Nudge" Effect

Think of the filament as a heavy, sleeping cat lying on a spring. Suddenly, someone starts tapping the spring with a stick.

The First Tap: A coronal jet (a fast stream of plasma moving at about 63 km/s) hits the filament. The filament wakes up and starts to wobble.
The Second Tap: Another jet (moving at 66 km/s) hits it later. The wobble gets bigger and slower.
The Big Push: A third, much faster jet (zooming at 203 km/s) hits the filament. This is the final nudge that sends the cat flying.

The researchers noticed something cool about the wobble: as the filament rose, its oscillations grew. The time it took to swing back and forth got longer (increasing from about 50 minutes to 77 minutes), and the distance it swung (the amplitude) grew from 4.11 Mm to 12.56 Mm.

Why Did the Wobble Get Bigger?

Here is the clever part of the explanation. The authors compared the filament to a spring oscillator. Imagine a spring holding a weight. If you slowly stretch the spring out, the "springiness" (the restoring force) gets weaker. When the spring is weak, the weight swings slower and wider.

In the Sun's case, as the jets pushed the filament higher, the magnetic forces holding it down (the "spring") got weaker. Because the forces were getting weaker, the filament's wobbles naturally became larger and slower. This "growing wobble" is a key clue that the filament is about to erupt.

The "Tipping Point" (Torus Instability)

The filament didn't just float away; it hit a specific height where the rules of the game changed. The researchers calculated that when the filament reached a height of 118 Mm (corrected from a projected 83 Mm), the background magnetic field became too weak to hold it down. This is called the torus instability threshold (specifically when the "decay index" hits 1.3).

Once the filament crossed this invisible line, it didn't just rise; it erupted rapidly. The team used powerful computer simulations (using the MPI-AMRVAC code) to recreate this event. Their simulations confirmed that the jets were the trigger, and the weakening magnetic forces were the reason the wobbles grew.

What It Was Not

The paper is very careful to rule out some other ideas:

It wasn't a "Kink" explosion: Sometimes filaments twist like a pretzel until they snap (kink instability). But the researchers checked the magnetic twist and found it was less than 2 turns, which is too low for a kink explosion. So, they ruled that out.
It wasn't a standard flare start: Usually, when a filament rises, bright loops (post-flare loops) appear immediately. But in this case, the filament rose slowly for a while before any bright loops appeared. The bright loops only showed up about an hour after the eruption really got going. This suggests the jets and the magnetic instability did the heavy lifting, not a standard magnetic reconnection flare starting the whole thing.

The Takeaway

This study suggests that if you see a solar filament starting to wobble with growing amplitude and period, it might be getting ready to blow its top. The "nudging" from coronal jets can push a stable filament over the edge, and the changing wobble is the warning sign.

While the paper doesn't claim to have solved every solar eruption, it provides strong evidence—backed by both real-world observations and computer simulations—that these growing oscillations are a reliable precursor. It's like hearing a creaking floorboard get louder and slower; you know the floor is about to give way.

Technical Summary: Successive Coronal Jets as Novel Facilitators for Filament Oscillation and Eruption

Problem Statement
Solar filament eruptions are primary drivers of coronal mass ejections (CMEs) and space weather, yet the physical mechanisms triggering the transition from stable suspension to eruption remain incompletely understood. Specifically, the early-stage processes that drive a magnetic flux rope toward instability, along with their observable signatures, are poorly characterized. While pre-eruptive filament oscillations (both longitudinal and transverse) are known precursors, the physical link between these oscillations, their growth in amplitude and period, and the subsequent eruption has not been definitively established.

Methodology
The study employs a multi-instrument observational approach combined with advanced numerical simulations:

Observations: The authors analyzed coordinated data from the Solar Dynamics Observatory (SDO/AIA and HMI), STEREO (EUVI and COR2), Hinode (XRT), the New Vacuum Solar Telescope (NVST), and the Solar Magnetic Activity Research Telescope (SMART). This dataset provided multi-wavelength (H $\alpha$ , EUV, soft X-ray) and multi-perspective views of a C-shaped filament event on February 23–24, 2019.
Kinematic Analysis: Time-distance diagrams and time-slice analyses were constructed to track filament height, oscillation amplitudes, and periods. A damped harmonic oscillator model ( $x(t) = A_0e^{-bt} \cos(pt + \phi_1) + ct + d$ ) was used to fit plasma motions.
Magnetic Modeling: A 3D magnetofrictional (MF) simulation using the MPI-AMRVAC code reconstructed the pre-eruptive magnetic flux rope via helicity condensation from HMI vector magnetograms.
MHD Simulations: To validate the eruption mechanism, 3D magnetohydrodynamic (MHD) simulations were performed. These models included gravity, radiative loss, thermal conduction, and empirical coronal heating. A localized periodic heating source was introduced at the flux rope footpoint to simulate successive thermal jets, allowing the study of the coupled system's evolution over 9.5 hours.

Key Results

Successive Jet Interaction: The filament was activated by three successive coronal jets originating from weak negative-polarity regions beneath the filament. These jets impacted the filament sequentially, inducing a gradual rise and exciting transverse oscillations.
Growing Oscillations: As the filament rose due to jet impacts, both transverse and longitudinal oscillations exhibited a significant increase in amplitude and period.
- Transverse oscillations increased from a pre-jet period of ~50 min and amplitude of ~4 Mm to a post-jet period of ~77 min and amplitude of ~12.5 Mm.
- Longitudinal oscillations also showed a pronounced amplitude increase.
Torus Instability Trigger: The filament's slow rise, driven by jets, continued until it reached a height of approximately 118 Mm. At this altitude, the decay index of the background magnetic field reached 1.3, exceeding the torus instability threshold. This triggered the rapid eruption phase.
Force Analysis: MHD simulations revealed that as the filament rises, the restoring forces governing oscillations (specifically the Lorentz force within the flux rope and the gravitational force) progressively weaken. This weakening is analogous to a spring oscillator with a decreasing spring constant, naturally leading to increased oscillation amplitude and period.
Reconnection Timing: Soft X-ray observations and simulation data indicated that magnetic reconnection (manifested as post-flare loops) occurred in a delayed, stepwise manner after the filament had been lifted by jet impacts and reached the torus instability height. This suggests reconnection is a consequence of the eruption rather than the primary driver of the initial slow rise.
Instability Type: The magnetic twist in the flux rope remained below the kink instability threshold (< 2 turns), and no helical structures were observed, confirming that torus instability, rather than kink instability, was the dominant driver.

Significance and Claims
The paper claims to provide the first direct evidence that growing oscillations (increasing amplitude and period) serve as a reliable observable precursor for filament eruptions. The study demonstrates that successive coronal jets can act as facilitators, disturbing a stable filament and exciting oscillations that grow as the restoring forces weaken during the ascent.

The authors conclude that the physical mechanism involves a progressive reduction in restoring forces (Lorentz and gravity) as the filament rises, which naturally explains the observed growth in oscillation parameters. This finding enhances the ability to predict solar eruptions by identifying specific pre-eruptive fine structures and kinematic behaviors. The work distinguishes itself from reconnection-favored models (e.g., tether-cutting) by showing that in this event, the initial rise was jet-driven, with torus instability and subsequent reconnection occurring only after the filament reached a critical height. The authors note that while jets are a primary facilitator in this case, other mechanisms (mass drainage, surges, waves) may also induce similar growing oscillations.

The "Nudge-Nudge" Effect

Why Did the Wobble Get Bigger?

The "Tipping Point" (Torus Instability)

What It Was Not

The Takeaway

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