Viewing archive of Friday, 17 October 2025

Daily bulletin on solar and geomagnetic activity from the SIDC

Issued: 2025 Oct 17 1235 UTC

SIDC Forecast

Solar flares

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

Geomagnetism

Active conditions expected (A>=20 or K=4)

Solar protons

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

	10cm flux	Ap
17 Oct 2025	160	018
18 Oct 2025	162	023
19 Oct 2025	164	021

Solar Active Regions and flaring

Solar flaring activity was moderate over the past 24 hours with 4 M-class flares recorded. The largest flare was an M1.5 flare (SIDC Flare 5811) peaking on October 17 at 01:28 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. SIDC Sunspot group 621 (NOAA Active region 4248), another complex region on disk, was stable. A new region rotated over the east solar limb and was numbered SIDC Sunspot Group 672 (NOAA Active region 4256). 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.

Coronal mass ejections

The partial halo Coronal Mass Ejections (CME) directed the west that was reported yesterday, first detected in SOHO/LASCO-C2 data from 15:00 UTC on October 15 has been further analysed and a glancing blow may be possible from late on October 18. No new Earth directed CMEs were observed.

Coronal holes

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

Solar wind

The solar wind conditions reflected a slow solar wind regime with a solar wind speed of around 400 km/s and maximum magnetic field strength of 5nT. From 09:00 UTC October 17 a jump in the magnetic field strength was observed with values up to 14 nT. This is likely the influence of a glancing glow from one of the CMEs from October 13. During this time, the solar wind speed remain around 400 km/s. Over the next 24 hours the solar wind conditions are expected to continue to be slightly perturbed due to the passing of the current weak magnetic field structure and another possible glancing blow CME arrival on October 18 from the partial halo CME observed on October 15.

Geomagnetism

Geomagnetic conditions were at quiet to unsettled levels globally and locally (Kp 1-3, K Bel 1-3). Unsettled to active conditions are expected on October 17, with periods of minor storm conditions (Kp 5) possible on October 18 in response to the possible CME arrival.

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 exceeded the 1000 pfu threshold. The greater than 2 MeV electron flux is expected to again exceed the 1000 pfu threshold over the next 24 hours. The 24-hour electron fluence was at moderate levels and is expected to be at moderate levels over the next 24 hours.

Today's estimated international sunspot number (ISN): 119, based on 08 stations.

Solar indices for 16 Oct 2025

Wolf number Catania	///
10cm solar flux	161
AK Chambon La Forêt	010
AK Wingst	004
Estimated Ap	003
Estimated international sunspot number	133 - Based on 18 stations

Noticeable events summary

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

All times in UTC

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