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On the Relationship between Solar Spicules and Propagating Coronal Disturbances: The Role of Shocks

By combining high-resolution multiwavelength observations with radiative magnetohydrodynamic simulations, this study demonstrates that shock waves generated in the chromosphere drive solar spicules and evolve into large-amplitude compressive waves in the corona, thereby establishing a physical link between spicules and propagating coronal disturbances that contribute to mass and energy transport into the solar wind.

Original authors: Ravi Chaurasiya, Sankalp Srivastava, Piyali Chatterjee, Sahel Dey, Robertus Erdélyi, Ankala Raja Bayanna

Published 2026-06-02

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CC BY 4.0

Original authors: Ravi Chaurasiya, Sankalp Srivastava, Piyali Chatterjee, Sahel Dey, Robertus Erdélyi, Ankala Raja Bayanna

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 busy, multi-story building. At the bottom floor (the surface), the "plumbing" is churning with hot gas and magnetic forces. This paper investigates how a specific event happening on the lower floors—tiny, jet-like fountains of gas called spicules—might be the same force that creates ripples and waves traveling all the way to the roof (the corona).

Here is the story of what the researchers found, using simple analogies:

1. The Mystery: Two Phenomena, One Connection?

Scientists have long known about two things happening on the Sun:

Spicules: These are like sudden, powerful geysers shooting up from the Sun's lower atmosphere (chromosphere). They shoot up fast, then fall back down.
PCDs (Propagating Coronal Disturbances): These are ripples or waves of brightness moving through the Sun's upper atmosphere (corona).

The big question was: Are these two things related? Do the geysers cause the ripples, or are they just happening at the same time by coincidence?

2. The "Shockwave" Trigger

The researchers used high-powered telescopes to watch the Sun and supercomputer simulations to model what's happening inside. They discovered that the answer lies in shockwaves.

The Analogy: Imagine clapping your hands underwater. The sound wave travels out, but if you clap hard enough, it creates a "shockwave"—a sudden, sharp pressure change.
What happened on the Sun: The Sun's surface is constantly vibrating (like a drum being hit). These vibrations travel upward. As they move into the thinner, upper layers of the atmosphere, they get squeezed and steepen, turning into sharp shockwaves.
The Result: These shockwaves act like a sudden kick. They hit the gas at the bottom, shooting it upward to create a spicule (the geyser).

3. The "Domino Effect"

The paper argues that the spicule and the coronal ripple are actually two sides of the same coin.

The Chain Reaction: The same shockwave that kicks the gas up to make the spicule doesn't stop there. It keeps traveling upward.
The Transformation: As this shockwave moves from the lower atmosphere into the upper atmosphere (the corona), it changes shape.
- In the lower atmosphere, it's a sharp "kick" that creates the geyser.
- In the upper atmosphere, it smooths out a bit but remains a powerful, compressive wave. This is what we see as the PCD (the ripple in the corona).

Think of it like a surfer riding a wave. The surfer (the spicule) is launched by the wave's energy. The wave itself (the shock) keeps moving forward, creating a disturbance in the water further out (the PCD). They are part of the same continuous event.

4. The "Traffic Jam" of Time

The researchers also looked at the "rhythm" of these events.

Lower Down: The vibrations start with a rhythm of about 5 minutes (like a steady heartbeat).
Higher Up: As these waves travel up through the Sun's atmosphere, the rhythm slows down to 10 minutes or more.
The Analogy: Imagine a crowd of people running up a very steep, slippery hill. The fast runners at the bottom get separated from the slower ones as they climb. The "pack" spreads out, and the time between the leaders and the followers gets longer. This is what happens to the waves as they move through the Sun's different layers.

5. Why Does This Matter? (The "Solar Wind" Connection)

The Sun is constantly blowing a "wind" of particles into space (the solar wind), which affects Earth's weather (space weather). Scientists have been trying to figure out where all the mass for this wind comes from.

The Finding: The study calculated that these shock-driven events (the geysers and the ripples) are powerful enough to push a significant amount of solar material upward.
The Conclusion: It turns out that the same mechanism that creates the spicules and the coronal ripples is also a major contributor to feeding the solar wind. The "kick" that launches the geyser is strong enough to push material all the way out into space.

Summary

In short, this paper shows that shockwaves are the master key. They start at the bottom, shoot up a jet of gas (a spicule), and then continue upward as a wave (a PCD). It's not two separate events; it's one continuous chain reaction that helps explain how the Sun heats its upper atmosphere and pushes material into space.

Technical Summary: On the Relationship between Solar Spicules and Propagating Coronal Disturbances: The Role of Shocks

Problem Statement
Solar spicules and propagating coronal disturbances (PCDs) are ubiquitous dynamic features of the solar atmosphere. While spicules are known to play a potential role in mass and energy transport into the corona, and PCDs are observed as intensity perturbations in coronal structures, the precise physical connection between them remains an open question. Previous studies have proposed various drivers for spicules, including shock waves, Alfvén waves, and magnetic reconnection, but a comprehensive physical picture linking shock-driven spicules in the lower atmosphere to PCDs in the corona has been missing. Understanding this link is crucial for determining whether spicules contribute to heating the solar corona and driving the solar wind.

Methodology
The authors employed a dual approach combining high-resolution multi-wavelength observations with two-dimensional radiative magnetohydrodynamic (rMHD) simulations.

Observations: Coordinated data were analyzed from the Swedish 1-m Solar Telescope (SST) and the Solar Dynamics Observatory (SDO) for NOAA Active Region 12760. The study utilized H $\alpha$ and Ca II 8542 $\mathring{A}$ spectral lines to probe the chromosphere and SDO/AIA 171 $\mathring{A}$ channels for the lower corona. Key analytical techniques included:
- Inspection of $\lambda-t$ diagrams to identify "sawtooth" patterns characteristic of shock waves at spicule footpoints.
- Construction of space-time ( $x-t$ ) maps to track the trajectories and velocities of spicules and PCDs.
- Multi-height wavelet analysis of Doppler velocities and intensity signals to determine dominant periodicities.
- Linear Force-Free Field (LFFF) extrapolation to trace magnetic field-aligned trajectories for coronal signal analysis.
Simulations: The authors utilized the Pencil Code to perform 2D radiative MHD simulations covering a vertical range from 5 Mm below the photosphere to 31 Mm above. The model included Spitzer thermal conduction, an ionized equation of state, detailed LTE radiative transfer, and tabulated radiative cooling. Two models were compared with imposed vertical background magnetic fields of $B_{imp} = 10$ G and $B_{imp} = 50$ G. The simulations were analyzed over a 60-minute time series to track the evolution of shocks, spicules, and synthetic EUV emission.

Key Results

Shock-Driven Spicule Formation: Observations revealed that spicule footpoints spatially coincide with locations exhibiting chromospheric shock signatures (sawtooth patterns in $\lambda-t$ diagrams). The simulations confirmed that photospheric oscillations leak into the chromosphere, steepen into non-linear shock waves, and drive spicular jets. The tips of these spicules coincide with the locations of detected slow shocks.
Transition to Coronal Disturbances: The study demonstrates that the same acceleration fronts driving spicules propagate upward into the corona. In the corona, these fronts manifest as intensity enhancements (PCDs). Depending on the magnetic field strength and ambient conditions, these fronts may either remain as shocks or transition into large-amplitude non-linear compressive MHD waves.
- In the $10$ G simulation, shock fronts transition to non-linear compressive waves at higher altitudes.
- In the $50$ G simulation, this transition occurs at lower heights, likely due to the suppression of convective power by the stronger magnetic field.
Velocity and Periodicity Evolution:
- Velocities: Observed spicules had projected velocities of $\sim 7.9$ –$15.9$ km s $^{-1}$ , while associated PCDs moved at $\sim 38$ –$45$ km s $^{-1}$ . Simulations showed similar trends, with PCD speeds varying based on magnetic field strength (e.g., $95.8$ km s $^{-1}$ for $10$ G vs. $26.5$ km s $^{-1}$ for $50$ G at specific heights).
- Periodicity: Wavelet analysis showed a dominant $\sim 5$ -minute period in the lower chromosphere (consistent with p-mode leakage), which evolved into longer periods ( $\ge 10$ minutes) in the corona. This shift is attributed to dispersive propagation in a stratified medium.
Mass Flux Estimates:
- The simulations calculated a net upward mass flux of $\langle \rho u_z \rangle_t \sim (1.1\text{--}3.5) \times 10^{-11}$ g cm $^{-2}$ s $^{-1}$ .
- When converted to a mass-loss rate per unit solid angle, the simulation results yielded $(6 \times 10^{10}\text{--}2 \times 10^{11})$ g s $^{-1}$ sr $^{-1}$ , which is comparable to the canonical solar wind mass-loss rate ( $\dot{M}_{WN} \sim 7 \times 10^{10}$ g s $^{-1}$ sr $^{-1}$ ).
- The authors note that simple slope-based mass flux calculations from $t-z$ images (ignoring return flows) significantly overestimate the net flux, but the physically averaged simulation results align well with solar wind requirements.

Significance and Claims
The paper claims to provide a unified physical scenario linking shock-driven spicules and PCDs. The primary contribution is demonstrating that chromospheric shocks, generated by convective motions and p-mode leakage, serve as the common driver for both phenomena. As these shocks propagate upward, they lift chromospheric plasma to form spicules and simultaneously generate compressive disturbances in the corona.

The authors assert that:

Spicules and PCDs are different manifestations of the same underlying shock-driven dynamics operating across multiple atmospheric layers.
The transition from shocks to non-linear compressive waves in the corona depends on magnetic field strength and coronal conditions.
These shock-driven mechanisms are capable of transporting sufficient mass flux to contribute significantly to the solar wind, supporting the hypothesis that spicules play a role in solar wind acceleration.
The study bridges a gap in previous literature by directly tracing the evolution of shock-driven dynamics from the low chromosphere to the corona using both high-resolution observations and advanced simulations, moving beyond studies that primarily focused on the upper chromosphere and transition region.

The authors conclude that while their work establishes a strong link for shock-driven events, further investigation is needed to determine if other classes of spicules exhibit similar connections and to quantify the total energy flux carried by these disturbances.