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Daily bulletin on solar and geomagnetic activity from the SIDC

Emesso: 2025 Oct 18 1235 UTC

SIDC Forecast

Brillamenti solari

M-class flares expected (probability >=50%)

Geomagnetism

Minor storm expected (A>=30 or K=5)

Protoni solari

Warning condition (activity levels expected to increase, but no numeric forecast given)

	10cm flux	Ap
18 Oct 2025	168	040
19 Oct 2025	171	035
20 Oct 2025	173	029

Solar Active Regions and flaring

Solar flaring activity was moderate over the past 24 hours with 10 M-class flares recorded. The largest flare was an M1.5 flare (SIDC Flare 5830) peaking on October 18 at 10:51 UTC, which was produced by SIDC Sunspot Group 639 (NOAA Active Region 4246). This is the most complex on disk and was responsible for all of the M-class flaring activity and is now rotating over the west limb. SIDC Sunspot group 621 (NOAA Active region 4248), another complex region on disk, was stable and quiet. A new region rotated over the east solar limb and was numbered SIDC Sunspot Group 674 (NOAA Active region 4257). A new region also emerged in the west quadrant and was numbered SIDC Sunspot Group 673 (NOAA Active region 4258). These and the remaining regions on disk were mostly quiet and either stable or in decay. The solar flaring activity is expected to be moderate over the next 24 hours, with M-class flares expected and a chance for X-class flares.

Espulsioni di massa coronale

No new Earth directed Coronal Mass Ejections (CMEs) were observed.

Fori coronali

SIDC Coronal Hole 126 (extended equatorial coronal hole with a negative polarity) continues to transit the central meridian since October 16.

Vento solare

The solar wind conditions reflected ongoing transient magnetic features, likely associated with the CMEs from October 13-15. The magnetic field was around 10 nT over the first half of the period and increased to a maximum of 20 nT around 08:30 UTC October 18. The Bz was mostly positive with an extended period of negative Bz between 04:00 and 07:00 UTC October 18 with a minimum value of -12 nT. The solar wind speed was stable around 400 km/s but increased from 06:00 UTC on October 18 to around 500 km/s at the end of the period. Over the next 24 hours the solar wind conditions are expected to continue to be slightly perturbed due to further influence from the glancing blow CME arrival from the partial halo CME observed on October 15. From late October 19, the high-speed stream associated with the negative polarity coronal hole (SIDC Coronal Hole 126) is also expected to arrive.

Geomagnetism

Geomagnetic conditions were at quiet to unsettled levels on October 17. From October 18 the geomagnetic conditions increased to active levels with one period of minor storm conditions (Kp 5) globally between 06:00 and 09:00 UTC. Locally active conditions were reached (K Bel 1-4). Minor storm conditions (Kp 5) are expected on October 18 and 19 in response CME influence and arrival of the high-speed stream arrival, with periods of moderate storm conditions possible (Kp 6).

Proton flux levels

The greater than 10 MeV proton flux was below the 10 pfu threshold over the past 24 hours. It is expected to remain below this threshold level over the next 24 hours. There is a small chance of an increase related to any high-level flaring, particularly from SIDC Sunspot Group 639 (NOAA Active Region 4246).

Electron fluxes at geostationary orbit

The greater than 2 MeV electron flux measured by GOES 18 and GOES 19 briefly exceeded the 1000 pfu threshold. The greater than 2 MeV electron flux is expected to again be at or just below the 1000 pfu threshold over the next 24 hours. The 24-hour electron fluence was at moderate levels and is expected to be at low to moderate levels over the next 24 hours.

Today's estimated international sunspot number (ISN): 115, based on 13 stations.

Solar indices for 17 Oct 2025

Wolf number Catania	131
10cm solar flux	164
AK Chambon La Forêt	023
AK Wingst	009
Estimated Ap	010
Estimated international sunspot number	118 - Based on 14 stations

Noticeable events summary

Provided by the Solar Influences Data analysis Center© - SIDC - Processed by SpaceWeatherLive

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