UPDATED - For older posts, please scroll down
UPDATE 4 November 2025 at 22:45UTC - The Sun produced a second X-class flare, just a few hours after the X1.8 event discussed underneath. The X1.1 flare peaked at 22:01 UTC. However, it did NOT have NOAA 4274 as its source, but rather an active region just behind the southeast solar limb as can be seen in the GOES/SUVI images below showing the flare in extreme ultraviolet (EUV) near its peak time: left at temperatures around 80.000 degrees, and on the right at temperatures of several million degrees. The diffraction patterns in the EUV images are image artifacts, and are not related to the flare itself - See this STCE newsitem for more info. A proton event from this eruption is unlikely due to its location, and any associated coronal mass ejection (CME) is very likely not earth-directed. More information will be given by the SIDC forecaster as the region rotates over the east limb.
The X-class flare affected the lower frequency portion of the High Frequency communication band (HF Com ; 3 - 30 MHz) mainly over the Pacific Ocean and New-Zealand. The effects of the X1 flare on HF Com can be seen in this D-RAP map (NOAA/SWPC). An advisory to civil aviation has been issued (PECASUS).
Original 4 November 2025 at 20:45UTC - Active region NOAA 4274 (SIDC Sunspot Group 687) is the return of the flare-productive NOAA 4246. That region was the source of 27 M-class flares which it produced during its transit over the solar disk from 10 to 19 October (see this STCE newsitem). While it was on the Sun's far side, it continued to produce strong eruptions, based on the numerous coronal mass ejections (CMEs) that were observed. Those were obviously directed away from the Earth. But now that active region has returned again and it is still very active: It has gotten a new number, but has clearly retained its old habits as it has just produced an X-class flare.
This eruption registered as an X1.8 that peaked at 17:34 UTC on 4 November (GOES). The SDO images above show NOAA 4274 in white light (left) as well as its complex magnetic structure (right; white denotes field lines coming out of the solar surface, black represent magnetic field lines returning to the Sun). The region harbors a delta structure (see the Mount Wilson classification) which in combination with the relatively large size of the region, can produce very strong flares. The GOES/SUVI images below show the flare in extreme ultraviolet (EUV) near its peak time: left at temperatures around 80.000 degrees, and on the right at temperatures of several million degrees. The diffraction patterns in the EUV images are image artifacts, and are not related to the flare itself - See this STCE newsitem for more info.
Coronagraphic images by STEREO-A -which is now leading the Earth by about 49° (map)- shows a relatively fast and wide CME, with a preliminary speed around 800 km/s and a width of around 100°. In view of the location of NOAA 4274 on the solar disk, this suggests that there's a small chance the earth environment may receive a glancing blow from this CME, albeit a nearby coronal hole (SolarMap) may divert it further away from Earth. Further analysis and images by the SOHO/LASCO coronagraphs are necessary before the SIDC SWx forecaster can make a final decision. Stand-by for updates.
No proton event has been observed yet, with the greater than 10 MeV proton flux remaining close to background levels (GOES). Mild enhancements of the radio flux at various frequencies have been observed (NOAA/USAF). Also the 10.7cm solar radio flux at 18UTC was affected, being nearly 40% above its value from the preceding days (Penticton, Canada; 183 sfu compared to 133 sfu). The radiospectrogram underneath was obtained by an eCallisto station in Mexico and shows strong Type III radio bursts between 17:24 and 17:28UTC. The Type II and Type IV bursts are not so obvious, if any (see the STCE SWx Classification page). Note that the bandwidth of this station is quite narrow, spanning only about 40 MHz. The horizontal axis represents time (from 17:14 to 17:59 UTC), the vertical axis is the frequency, with the highest values on top. The flare started (in soft x-rays) at 17:15 UTC, peaked at 17:34 UTC, and ended at 17:51 UTC.
The X-class flare affected the lower frequency portion of the High Frequency communication band (HF Com ; 3 - 30 MHz) mainly over South-America and the eastern portion of the Pacific Ocean. The effects of the X1 flare on HF Com can be seen in the D-RAP map underneath (NOAA/SWPC). An advisory to civil aviation has been issued (PECASUS). In view of its current size and complex magnetic structure, NOAA 4274 is likely to produce more strong flares during the next few days.
