In August 2024, the sun continued to display high levels of sunspot activity, reaching a 20-year high in sunspot numbers. Despite this recent surge in solar activity, none of the solar flares observed in the current Solar Cycle 25 have managed to surpass the two record-breaking solar flares that occurred in September 2017. One of these flares, which took place on September 10, 2017, still holds several unbroken records.
The solar flares in September 2017 occurred during the declining phase of the previous solar cycle, Solar Cycle 24, which had peaked in 2014. During this period of lower solar activity, an active region known as AR 12673 emerged rapidly and produced a series of powerful X-class solar flares. The most notable of these flares occurred on September 6 and September 10, 2017. Initially reported as X8.2 and X9.3, these flares were later reclassified as X13.3 and X11.8 following a flare recalibration by NOAA in 2020. These flare classes have yet to be surpassed in the current solar cycle, despite increased solar activity levels.
The second of the two flares on September 10, 2017, was particularly significant. This solar flare erupted over the western edge of the sun, with part of its footprint obstructed from view. The flare set multiple records, including the fastest magnetic emergence, fastest coronal mass ejection (CME) acceleration, and strongest long-duration gamma ray source.
The rapid emergence of magnetic field in the active region AR 12673 leading up to the solar flares was unprecedented. The magnetic field of sunspots, regions of strong magnetic field on the sun’s surface, plays a crucial role in the generation of large solar flares. The fast emergence of magnetic field in AR 12673 was instrumental in enabling the largest flares of the solar cycle.
Solar flares are often associated with CMEs, eruptions of solar plasma from the sun’s atmosphere. The solar flare on September 10, 2017, triggered a large CME above the western edge of the sun, with the fastest CME acceleration ever observed. This powerful event also produced a long-duration gamma ray source, emitting gamma rays for over 12 hours, setting a new record for the strongest gamma ray source observed for an extended period.
The solar flare from September 10, 2017, was extensively studied across various wavelengths of light, from radio waves to gamma rays. The event was observed by numerous solar telescopes both on the ground and in space, generating a wealth of data for scientists to analyze. This flare became the most published solar flare of all time, with over a hundred academic publications dedicated to studying different aspects of the event.
As Solar Cycle 25 progresses, with solar activity surpassing the levels of the previous cycle, researchers anticipate more strong solar flares in the coming years. However, whether any of these future flares will break the records set by the active region AR 12673 and the September 10, 2017 flare remains uncertain. Solar physicist Dr. Ryan French, who has conducted extensive research on solar phenomena, emphasizes the importance of ongoing observation and study of solar flares to better understand these dynamic events.
In conclusion, the solar flare that occurred on September 10, 2017, marked a significant event in solar physics, setting multiple records and garnering widespread scientific interest. As researchers continue to monitor solar activity in Solar Cycle 25, they remain hopeful for new discoveries and insights into the behavior of our local star, the sun.