Viewing archive of Wednesday, 17 September 2025

Daily bulletin on solar and geomagnetic activity from the SIDC

Issued: 2025 Sep 17 1231 UTC

SIDC Forecast

Solar flares

C-class flares expected, (probability >=50%)

Geomagnetism

Quiet (A<20 and K<4)

Solar protons

Quiet

	10cm flux	Ap
17 Sep 2025	136	008
18 Sep 2025	136	007
19 Sep 2025	136	005

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 8 numbered sunspot groups were identified on the visible solar disk, most classified as magnetic type beta. The strongest activity was a C3.8 flare with peak time at 13:14 UTC on Sept 16. The flare was produced by SIDC Sunspot Group 637 (NOAA Active Region 4220). This region together with SIDC Sunspot Group 643 (NOAA Active Region 4223) was responsible for most of the flaring activity over the past 24 hours. SIDC Sunspot Group 621 (NOAA Active Regions 4216, 4222) and SIDC Sunspot Group 640 (NOAA Active Region 4217) remained the largest regions on the visible solar disk. SIDC Sunspot Group 637 (NOAA Active Region 4220) and SIDC Sunspot Group 642 (NOAA Active Region 4221) have exhibited further growth. The solar flaring activity over the next 24 hours is expected to remain at low levels with very likely C-class flares and chances for isolated 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) remained under the influence of a high speed stream associated with the negative polarity SIDC Coronal Hole 116. The solar wind speed was predominantly in the range of 600 km/s to 750 km/s. The magnitude of the interplanetary magnetic field, B, was at nominal levels with a maximum of 5.5 nT and a minimum Bz component of - 4.5 nT. The B field phi angle remained predominantly in the negative sector (directed towards the Sun). The solar wind conditions are expected to continue to be under a waning HSS influence over the next 24 hours and gradually return towards slow solar wind background by Sept 19.

Geomagnetism

The global geomagnetic conditions over the past 24 hours were at active levels with only quiet to unsettled conditions registered locally over Belgium. The global geomagnetic conditions over the next 24 hours are expected to be predominantly at quiet to unsettled levels with small chances for isolated active periods.

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 electron flux (as measured by GOES 18 and GOES 19) 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 has reached moderate levels and is expected to remain at moderate levels in the next 24 hours.

Today's estimated international sunspot number (ISN): 125, based on 13 stations.

Solar indices for 16 Sep 2025

Wolf number Catania	142
10cm solar flux	135
AK Chambon La Forêt	020
AK Wingst	016
Estimated Ap	018
Estimated international sunspot number	128 - Based on 23 stations

Noticeable events summary

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

All times in UTC

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