Solar radiation storm produced by a long-duration X1.9 solar flare from Active Region 4341 on January 18 reached S3 – Strong levels at 10:20 UTC on January 19 after the ≥10 MeV proton flux exceeded 1 000 pfu.
The flare peaked at 18:09 UTC on January 18 and was accompanied by Type II and Type IV radio emissions, a 3 200 sfu F10.7 radio burst with a Castelli-U signature, and a full-halo coronal mass ejection first observed in coronagraph imagery at approximately 18:30 UTC. The CME is expected to impact Earth on January 20.
Proton flux levels initially crossed the S1 – Minor threshold at 22:55 UTC on January 18, exceeded S2 – Moderate levels early on January 19, and continued rising steadily through the morning hours. At 10:20 UTC, ≥10 MeV protons surpassed 1 000 pfu, triggering an S3 alert issued at 10:29 UTC.
GOES-18 proton data show sustained increases across multiple energy channels, indicating an ongoing and well-developed solar energetic particle event. Elevated ≥50 MeV proton flux has also been observed, confirming the high-energy nature of the storm.
At S3 intensity, increased radiation exposure is possible for passengers and crew on high-latitude, high-altitude flights, while astronauts conducting extravehicular activities are exposed to significantly elevated radiation levels. Satellite systems may experience single-event upsets, noise in imaging sensors, and minor reductions in solar panel efficiency. Polar high-frequency radio propagation may become degraded or experience intermittent blackouts.
Solar radiation storms of S3 – Strong intensity are relatively rare space weather events. Based on long-term NOAA statistics, only a limited number of such storms usually occur during a full 11-year solar cycle, as they require efficient particle acceleration by strong solar eruptions and CME-driven shocks.
The radiation storm continues as the CME propagates through interplanetary space. Additional impacts are possible if enhanced solar wind conditions and southward magnetic field components accompany the CME’s arrival at Earth later on January 19 or January 20.
Further updates will follow as particle flux trends and CME-driven space weather conditions evolve.