Minor C9.9 solar flare erupts at 06:05 UTC on October 18, 2025

A minor C9.9 solar flare erupted at 06:05 UTC on October 18, 2025.

This event began at 05:43 UTC, peaked at 06:05 UTC, and ended at 06:19 UTC, originating from solar region 4246. Today’s flares include M1.0 (00:40 UTC, region 4246), M1.1 (02:39 UTC, region 4246), C2.9 (02:09 UTC, region 4246), C9.5 (02:24 UTC, region 4246), and C9.9 (06:05 UTC, region 4246).

In 24 hours to 00:30 UTC on October 18, solar activity increased to high levels due to numerous M-class flares. As region 4246 approached the western limb, some intermediate spot decay was observed, while regions 4248 and 4256 showed quiet conditions with minor changes in spot configuration.

There is a likelihood of minor to moderate (R1-R2) radio blackouts through October 18, with a slight chance for an isolated strong (R3) event. Probabilities decrease slightly from October 19 to 20 as active region 4246 moves beyond the western limb.

Active sunspot regions presently observed on the Earth-facing solar disk include AR 4246 (N24W81 – Beta-Gamma-Delta), AR 4248 (N07W54 – Beta-Gamma), AR 4250 (N04W45 – Alpha), AR 4252 (S13E01 – Beta), AR 4254 (N11E33 – Alpha), AR 4255 (S08E26 – Beta), AR 4256 (S15E52 – Beta), and AR 4257 (S08E75 – Alpha).

Over the past 24 hours, the greater than 2 MeV electron flux reached high levels, with a maximum flux of 3 330 pfu at 17:00 UTC on October 17. The greater than 10 MeV proton flux remained at background levels. The electron flux is forecast to decrease to normal to moderate levels on October 18 due to glancing CME effects, then return to high levels on October 19–20. There is a slight chance for a greater than 10 MeV proton event above the S1 – Minor levels through October 18.

Over the past 24 hours, solar wind parameters were nominal until 09:30 UTC on October 17, when an interplanetary magnetic field enhancement occurred, likely from a glancing CME. The total field rose from 6–12 nT, with the Bz component reaching -9 nT, and a further increase to 14 nT after 20:20 UTC. Solar wind speeds remained near 380 km/s. Possible enhancement is anticipated through October 18 due to earlier CME activity, followed by a transition to a negative polarity coronal hole high speed stream on October 19.

During the last 24 hours, geomagnetic field activity was quiet to unsettled. Unsettled to active geomagnetic conditions, with a chance for G1 – Minor storming, are expected on October 18 from glancing CME effects, possibly continuing into early October 19. Additional unsettled to active periods are expected with the arrival of a negative polarity coronal hole high speed stream on October 19.