Positive polarity CH HSS sparks G3 – Strong geomagnetic storm
A G3 – Strong geomagnetic storm is in progress on October 2, 2025, driven by a positive-polarity coronal hole high-speed stream (CH HSS). The U.S. Space Weather Prediction Center (SWPC) issued an active warning valid until 12:00 UTC, with aurora sightings possible as far south as Pennsylvania, Iowa, and Oregon.
Aurora seen by ISS astronaut Kimiya Yui on September 30, 2025. Credit: ISS/Kimiya Yui
Solar wind speeds remained elevated at 700–800 km/s on October 1, with a maximum of 880 km/s (547 miles/s) at 17:00 UTC. Overnight into October 2, solar wind speeds remained elevated and reached over 900 and up to 1 045 km/s on occasions.
The interplanetary magnetic field (IMF) showed total field strengths of 8–10 nT, with the north–south component (Bz) fluctuating between ±8 nT.
Elevated geomagnetic activity began at 08:55 UTC on September 29 and has persisted since, enhanced by Earth’s orientation near the fall equinox. Conditions intensified to G3 – Strong levels on multiple occasions.
The latest G3 storming event started at 05:59 UTC on October 2.
According to NOAA’s space weather scales, G3 – Strong geomagnetic storms can cause power-system voltage irregularities and false alarms on protection devices. Satellites may experience surface charging, orientation problems, and increased drag in low Earth orbit.
High-frequency radio may be intermittent, and GPS navigation can show increased range error or temporary signal loss. Aurora visibility during G3 storming extends significantly equatorward, with reports possible as far south as Pennsylvania, Iowa, and Oregon.
SWPC’s current forecast suggests active to G1–G2 levels may persist beyond the warning window, with continued disturbance expected through October 4 as Earth remains connected to the coronal hole.
皆さん、おはようございます！
— 油井 亀美也 Kimiya.Yui (@Astro_Kimiya) September 30, 2025
最近、オーロラが綺麗なので、運動の合間にタイムラプス映像の撮影をしてみました。
オーロラが波の様に押し寄せ、その後オーロラの海を航海している様な気持ちになる映像をお楽しみ下さい。
地球からパワーを貰いつつ、10月も一緒に頑張りましょう！ pic.twitter.com/nYO5NMHlya
Solar activity has been at moderate levels in 24 hours to 00:30 UTC on October 2, with several M-class flares observed from Region 4232 (beta-gamma-delta).
A Type II radio emission was detected at 02:09 UTC on October 2, with an estimated shock velocity of ~508 km/s, typically associated with coronal mass ejections (CME). The CME was confirmed as farsided and is not expected to affect Earth.
A continued alert is in effect for elevated >2 MeV electron flux, which exceeded 1 000 pfu beginning at 13:25 UTC on October 1. Fluxes reached a maximum of 3 601 pfu yesterday, increasing the risk of spacecraft charging. Proton flux remains near background levels, and the probability of an S1 – Minor solar radiation storm remains low.
I'm a dedicated researcher, journalist, and editor at The Watchers. With over 20 years of experience in the media industry, I specialize in hard science news, focusing on extreme weather, seismic and volcanic activity, space weather, and astronomy, including near-Earth objects and planetary defense strategies. You can reach me at teo /at/ watchers.news.
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