🔭 astrophysics

Energy Evolution from the Chromosphere to the Heliosphere in the 2021 October 28 Solar Eruption

This study analyzes the 28 October 2021 X1.0 solar eruption using multi-spacecraft observations to quantify various energy components, finding that the total released energy matches pre-event magnetic storage estimates and that CME kinetic and potential energy dominate the overall energy partition.

Original authors: Katharine K. Reeves, Daniel B. Seaton, Cynthia Cattell, Bin Chen, Liam David, Federico Fraschetti, Joe Giacalone, Phillip Hess, Andryi Koval, Dana W. Longcope, Surajit Mondal, Christopher S. Moore, So

Published 2026-05-18

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Katharine K. Reeves, Daniel B. Seaton, Cynthia Cattell, Bin Chen, Liam David, Federico Fraschetti, Joe Giacalone, Phillip Hess, Andryi Koval, Dana W. Longcope, Surajit Mondal, Christopher S. Moore, Sophie Musset, Tatiana Niembro, Daniel Pacheco, Yeimy J. Rivera, Soumya Roy, Xudong Sun, Durgesh Tripathi, Domenico Trotta, Matthew J. West, Sijie Yu, Chunming Zhu

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 as a giant, chaotic energy storage facility. Inside its atmosphere, magnetic fields act like twisted rubber bands, storing massive amounts of potential energy. Sometimes, these rubber bands snap, releasing that stored energy in a violent explosion known as a solar eruption.

This paper is a detailed "energy audit" of one specific, massive explosion that happened on October 28, 2021. The scientists wanted to answer a simple question: When the Sun snaps a magnetic rubber band, where does all that energy actually go?

Here is the breakdown of their investigation, using everyday analogies:

1. The Event: A Triple Threat

On that day, the Sun didn't just let off a little steam. It unleashed a "triple threat" event:

A Solar Flare: A sudden, intense flash of light (like a camera flash, but a billion times brighter).
An EUV Wave: A massive ripple moving across the Sun's surface, similar to a shockwave rippling through a pond after you drop a giant rock.
A Coronal Mass Ejection (CME): A giant bubble of solar gas and magnetic fields being hurled into space at over 2,000 kilometers per second. This is the "bullet" fired from the Sun.

2. The Detective Team: A Global View

To figure out where the energy went, the researchers didn't just look from Earth. They used a "constellation" of space telescopes and satellites, including:

Earth-based satellites: Watching from our backyard.
STEREO-A: A satellite that was off to the side, giving a side-view of the explosion.
Solar Orbiter: A spacecraft that was closer to the Sun (about 80% of the distance to Earth), acting like a close-up camera.

By combining these different angles, they could track the energy from the moment it was stored, through the explosion, and all the way out into space.

3. The Energy Budget: Where Did the Money Go?

The scientists treated the Sun's energy like a bank account. They calculated how much energy was stored before the explosion and then tried to account for every penny spent afterward. They looked at several "expenses":

The "Footprint" (Chromosphere): When the explosion happened, it heated the lower layers of the Sun's atmosphere. This is like the heat you feel when standing near a bonfire.
The "Flash" (Non-thermal particles): The explosion accelerated electrons and ions to near-light speeds. These are like tiny, super-fast bullets zipping around.
The "Ripple" (EUV Wave): The energy used to push that massive wave across the Sun's surface.
The "Bullet" (CME): The energy required to launch the giant bubble of gas into space. This includes the kinetic energy (how fast it's moving) and gravitational potential energy (the energy needed to lift it out of the Sun's gravity well).

4. The Big Discovery: The Bullet Wins

After doing the math, the researchers found a clear winner in the energy budget:

The Coronal Mass Ejection (the "bullet") took the lion's share of the energy.

The CME: About 75% to 80% of the total released energy went into launching the CME. It was the heavy lifter, carrying the vast majority of the power.
The Flare and Particles: The bright flash and the fast-moving particles only accounted for a small fraction (roughly 15-20%) of the total energy.
The Wave: The ripple on the surface was significant but still much smaller than the CME.

The Analogy: Imagine you have a savings account with $100. You decide to spend it all at once.

You spend $80 on a massive rocket launch (the CME).
You spend $15 on a fireworks display (the flare).
You spend $5 on a loud noise (the wave).
Conclusion: The rocket launch was the main event, not the fireworks.

5. The Journey into Space

The study didn't stop at the Sun. They tracked the CME as it traveled through space, passing two different spacecraft (Solar Orbiter and Wind).

They found that even as the CME traveled millions of miles, the energy remained mostly in the form of movement (kinetic energy). It didn't suddenly turn into heat or create a massive explosion of new particles along the way. The "bullet" kept its momentum, just slowing down slightly as it pushed through the solar wind, much like a car slowing down as it drives through thick fog.

Summary

This paper confirms that for this specific, massive solar eruption, the Sun's stored magnetic energy was primarily converted into the motion and lifting power of the ejected gas cloud (CME). While the bright flash and fast particles were dramatic and dangerous, they were essentially the "side effects" of the main event: the massive ejection of solar material into our solar system.

Technical Summary: Energy Evolution from the Chromosphere to the Heliosphere in the 2021 October 28 Solar Eruption

Problem Statement
Solar eruptions convert stored magnetic energy into thermal, kinetic, and gravitational potential energy, as well as accelerated particles. While previous studies (e.g., Emslie et al. 2004, 2005, 2012; Aschwanden et al. 2017) have attempted to characterize energy partitioning in solar eruptive events, a comprehensive accounting spanning the entire evolution from the corona to the heliosphere remains complex. This complexity arises because energy transforms through multiple states—such as chromospheric heating, flare loop radiation, and shock acceleration—and requires observations across diverse regimes. The specific event studied, the October 28, 2021 eruption (AR 12887), presented a unique opportunity for such a study due to its association with an X1.0 flare, a global EUV wave, and a fast Coronal Mass Ejection (CME) that caused the first Ground Level Enhancement (GLE) of Solar Cycle 25. Crucially, this event was observed by Solar Orbiter at approximately 0.8 au, nearly aligned with the Sun-Earth line, allowing for a multi-point, in-situ diagnosis of energy flux evolution.

Methodology
The authors performed a detailed energy budget analysis of the October 28, 2021 event, utilizing remote sensing and in-situ data from NASA's Heliophysics System Observatory. The study integrated observations from SDO (HMI, AIA), GOES (XRS, SUVI), STEREO-A (EUVI, COR), SoHO (LASCO), Solar Orbiter (STIX, SWA, MAG, EPD), and Wind (MFI, 3DP, SOSP).

The methodology involved calculating specific energy components:

Magnetic Energy: Nonlinear Force-Free Field (NLFFF) and potential field extrapolations were performed on SHARP data to estimate pre-event stored magnetic energy and free energy.
Non-thermal Particles: Energy in accelerated electrons was derived from STIX hard X-ray spectral fitting and EOVSA microwave gyrosynchrotron modeling. Non-thermal ion energy was estimated using a scaling law derived from RHESSI observations of previous events.
Bolometric and Chromospheric Energy: Bolometric energy was estimated via scaling laws relating GOES flux to total irradiance. Energy deposited in the chromosphere was calculated using the Ultraviolet Footpoint Calorimeter (UFC) method on AIA 1600 Å images.
Thermal Energy: Two independent methods were used: a single-loop approximation based on GOES X-ray flux (temperature and emission measure) and Differential Emission Measure (DEM) analysis using AIA and SUVI imaging data.
EUV Wave Energy: Wave energy was calculated by integrating kinetic, radiative, and conductive fluxes over the wave's volume and duration, treating the wave as a blast wave.
CME Kinetic and Potential Energy: CME mass was derived from white-light coronagraph images (STEREO-A COR2) using Thomson scattering, accounting for mass accumulation via a height-mass formula. Kinetic and gravitational potential energies were calculated as the CME propagated.
Heliospheric Fluxes and Shock Partition: In-situ data from Solar Orbiter (0.8 au) and Wind (1 au) were used to calculate energy fluxes (kinetic, enthalpy, magnetic, Poynting). The energy partition at the interplanetary shock (IP) was analyzed using Rankine-Hugoniot jump conditions, including contributions from energized protons and electrons.

Key Results

Magnetic Energy: The pre-event free magnetic energy in AR 12887 was estimated at $8.2 \pm 2.6 \times 10^{31}$ erg.
Flare Energetics: The total non-thermal energy in accelerated particles (electrons and ions) was $2.25 \pm 0.9 \times 10^{31}$ erg. The bolometric energy was estimated between $1.6$ and $3.0 \times 10^{31}$ erg. Energy deposited in the chromosphere was $1.7 \times 10^{31}$ erg (prompt + tail). Thermal energy in flare loops peaked at approximately $0.6 \times 10^{31}$ erg (GOES method) or $0.49 \times 10^{31}$ erg (DEM method).
EUV Wave: The total energy dissipated by the global EUV wave was calculated as $9.4 \pm 4.0 \times 10^{30}$ erg, dominated by kinetic energy flux.
CME Energy: The CME kinetic and gravitational potential energy was found to be the dominant component, with a total value of $9.75 \pm 3.6 \times 10^{31}$ erg. This value is consistent with the pre-event free magnetic energy estimate, suggesting that nearly all available magnetic energy was converted into the CME.
Heliospheric Evolution: In-situ measurements at 0.8 au and 1 au showed that the CME retained its kinetic energy dominance as it propagated. The shock at Solar Orbiter (0.8 au) converted upstream kinetic energy primarily into thermal energy, with a surprisingly small fraction (<5%) going into energizing particles. At Wind (1 au), the efficiency of particle energization was even lower.
Energy Partition: The study confirms that for this event, the CME (kinetic + potential) represents the majority of the released energy, significantly exceeding the energy in non-thermal particles and thermal radiation.

Significance and Claims
The paper claims to provide a "thorough accounting" of energy partitioning from the corona to the heliosphere for a single, well-observed event. The primary significance lies in the consistency of the results: the total energy released during the event aligns with estimates of the pre-event stored magnetic energy, and the CME kinetic plus potential energy dominates the energy budget. This finding supports the conclusions of Emslie et al. (2012) regarding the dominance of CME energy in eruptive flares, contrasting with some other studies (e.g., Aschwanden et al. 2017) that suggested a different partition.

The authors emphasize that the unique alignment of Solar Orbiter allowed for the first detailed diagnosis of the evolution of in-situ energy fluxes as a function of time and heliocentric distance for such an event. They note that the low efficiency of particle acceleration at the shock, particularly the lack of >100 keV ions at Solar Orbiter despite the high Mach number, suggests complex 3D shock geometry or local effects that require further simulation. The study concludes that the majority of the energy in this eruption was partitioned into the CME, a distribution that persisted as the CME evolved through the heliosphere.