This year has been quite eventful on the sun, as it has officially reached the peak of its approximately 11-year activity cycle, known as solar maximum. During 2024, the sun discharged more than 50 X-class solar flares — the most intense category of solar flare — towards Earth.
Solar flares are classified based on the intensity of X-rays emitted in a specific wavelength range (1 to 8 angstroms). The classification of solar flares follows a logarithmic scale, meaning that each class — C, M, and X — is ten times more potent than its predecessor. Additionally, solar flares can expel massive plasma clouds termed coronal mass ejections (CMEs), which can lead to geomagnetic storms and extensive auroras.
The video above showcases data from NASA’s Solar Dynamics Observatory Atmospheric Imaging Assembly (AIA). The panel on the left shows emissions from AIA 131 Å, and the right one from AIA 171 Å. These illustrate plasma at temperatures around 18 million and 1.8 million degrees Fahrenheit (10 million and 1 million degrees Celsius), respectively. Below, we will examine the ten most powerful solar flares recorded between Jan. 1 and Dec. 10, 2024.
10. X3.38 — Feb. 9
This X3.38 flare, which happened over the sun’s southwestern edge, would have registered significantly higher had much of the emission not been obscured by the sun’s edge. This flare serves as a notable example of a “coronal wave,” as coronal material in AIA 171 Å emissions appears to be almost “blown out of the way” by the initial flare.
During this significant flare on Feb. 9, similar to nearly all X-class flares, the intense and concentrated signal formed an “X” or “star” shaped diffraction pattern that radiated from the brilliant flare site observed in AIA 131 Å emission. This diffraction pattern is an artifact created by the telescope camera; it did not genuinely occur on the sun.
9. X3.48 — May 15
This is the first of four solar flares on this list that originated from solar active region AR 13664.
AR 13664 was a renowned and highly active region, generating 12 X-class solar flares within a span of just six days. The May 15 flare marked the last visible X-class flare from Earth, and it would have recorded a higher magnitude had it not been partially obscured by the sun’s western edge.
As the active region rotated behind the sun and reappeared two weeks later, it continued to generate substantial flares (under a new active region number). Observations from the European Space Agency’s Solar Orbiter also indicated large flares from the region during the time it was concealed from view from Earth.
8. X3.98 — May 10
This solar flare also stemmed from active region AR 13664. The flare resulted in a strong Earth-directed CME — one of several that erupted within a 48-hour timeframe. The CME originated from an optimal location on the sun, ensuring maximum effect on Earth.
As the series of CMEs impacted our planet on May 11-12, they triggered a G5 geomagnetic storm — the most powerful geomagnetic storm since 2003. This brought about widespread auroras at low latitudes, captivating millions across the globe.
7. X4.52 – May 6
A different flare earlier in May was emitted from active region AR 13663 — one active region lower than the source of the preceding two flares. While AR 13664 was actively generating eruptive flares in the sun’s southern hemisphere, AR 13663 unleashed a series of X-class solar flares from the northern hemisphere. Most of these flares, including this May 6 occurrence, did not result in notable Earth-directed coronal mass ejections.
6. X4.54 — Sept. 14
This solar flare generated a robust CME, directed over the sun’s eastern limb. For flares of this magnitude and greater, one can observe pixel saturation spilling over into adjacent pixels, creating periodic sharp and jagged saturation features that extend above and below the bright flare site.
5. X5.89 — May 11
Similar to the flare on May 6, this event originated from AR 13664. This flare also resulted in a coronal mass ejection, which was part of the sequence of CMEs contributing to the extreme and prolonged G5 geomagnetic storm directed at Earth.
Because the May 11 flare was located closer to the limb than the prior flare from the same active region, it was marginally less ideally positioned to affect us directly.
4. X6.37 – Feb. 22
Not all potent solar flares are fascinating. Even though this one came in at X6.37, it did not generate any Earth-directed CMEs and was not particularly remarkable.
3. X7.10 — Oct. 1
This flare is one of two on this list that originated from active region AR 13842, along with the most potent flare listed.
Neither of the two strongest flares from this active region directed intense geomagnetic storms at Earth. Nevertheless, smaller X-class flares from this same region later released the CMEs accountable for a significant G4 geomagnetic storm on Oct. 10, which, in turn, caused widespread low-latitude auroras worldwide.
This serves as a valuable lesson: The magnitude of solar flares is only weakly correlated with the likelihood of a flare-induced CME producing strong auroras. In this case, the larger flares had a lesser geomagnetic effect than the smaller flares.
2. X8.79 — May 14
This is the fourth and final flare on this list sourced from active region AR 13664, which has been undeniably the most X-class-productive area during this solar cycle (at least up until now). However, unlike the earlier flares that erupted from this region, the May 14 flare was contained, without a notable eruption. Consequently, the physical dimensions of the flare appear small, despite the intense X-ray emissions.
1. X9.0 — Oct. 3
Ultimately, the largest flare of the year thus far released an immense amount of energy — nine times the threshold required to qualify as an X-class flare. This was the third-largest solar flare since 2011 and the fifth-largest since 2005.
Will this be the most powerful solar flare we observe in Solar Cycle 25? As solar maximum proceeds into 2025, we will have to wait and see.