Viewing archive of Thursday, 18 September 2025

Daily bulletin on solar and geomagnetic activity from the SIDC

Issued: 2025 Sep 18 1231 UTC

SIDC Forecast

Solar flares

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

Geomagnetism

Quiet (A<20 and K<4)

Solar protons

Quiet

	10cm flux	Ap
18 Sep 2025	150	007
19 Sep 2025	152	005
20 Sep 2025	154	006

Solar Active Regions and flaring

Solar flaring activity was at low levels over the past 24 hours with only C-class flares identified. A total of 7 numbered sunspot groups were identified on the visible solar disk. Most regions have been classified as simple bipolar groups with magnetic type beta and SIDC Sunspot Group 607 (NOAA Active Region 4225) is a simple unipolar group, classified as magnetic type alpha. The strongest activity was a C2.8 flare (SIDC Flare 5513) with peak time at 00:04 UTC on Sept 18 produced by SIDC Sunspot Group 643 (NOAA Active Region 4223). Most of the detected flaring activity was produced by SIDC Sunspot Group 621 (NOAA Active Regions 4216) and SIDC Sunspot Group 637 (NOAA Active Region 4220) with the latter group exhibiting significant growth. The solar flaring activity over the next 24 hours is expected to be at low to moderate levels with very likely C-class flares and 51% chances for M-class flaring.

Coronal mass ejections

No Earth-directed coronal mass ejections (CMEs) have been identified in the available coronagraph imagery over the past 24 hours.

Solar wind

Over the past 24 hours the solar wind parameters (as measured by ACE) have registered an expected return towards slow solar wind conditions. The solar wind speed has declined from about 700 km/s to about 500 km/s at present. The magnitude of the interplanetary magnetic field, B, remained weak with a maximum of 4.7 nT and a minimum Bz component of - 4.4 nT. The B field phi angle remained predominantly in the negative sector (directed towards the Sun). The solar wind conditions are expected to be at background slow solar wind levels over the next days.

Geomagnetism

The geomagnetic conditions over the past 24 hours (both globally and locally over Belgium) were at quiet to unsettled levels. The geomagnetic conditions over the next days are expected to be predominantly quiet with possible isolated unsettled intervals.

Proton flux levels

Over the past 24 hours the greater than 10 MeV GOES proton flux has been at nominal levels and is expected to remain at nominal levels over the next days.

Electron fluxes at geostationary orbit

The greater than 10 MeV GOES electron flux has exceeded the 1000 pfu threshold over the last 24 hours and is expected to exceed the threshold again over the next 24 hours. The 24-hour electron fluence was at moderate levels and is expected to remain at moderate levels over the next days.

Today's estimated international sunspot number (ISN): 134, based on 11 stations.

Solar indices for 17 Sep 2025

Wolf number Catania	///
10cm solar flux	147
AK Chambon La Forêt	015
AK Wingst	011
Estimated Ap	010
Estimated international sunspot number	130 - Based on 21 stations

Noticeable events summary

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

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