Viewing archive of Tuesday, 16 September 2025

Daily bulletin on solar and geomagnetic activity from the SIDC

Issued: 2025 Sep 16 1231 UTC

SIDC Forecast

Solar flares

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

Geomagnetism

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

Solar protons

Quiet

	10cm flux	Ap
16 Sep 2025	126	020
17 Sep 2025	126	025
18 Sep 2025	126	011

Solar Active Regions and flaring

Solar flaring activity was at low levels over the past 24 hours. 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 C3.5 flare (SIDC Flare 5500) with peak time 18:31 UTC on Sept 15. The flare was produced from behind the west limb, possibly by SIDC Sunspot Group 631 (NOAA Active Region 4213). SIDC Sunspot Group 621 (NOAA Active Region 4216) and SIDC Sunspot Group 640 (NOAA Active Region 4217) are the largest regions on the visible solar disk with the latter contributing to most of the low flaring activity. SIDC Sunspot Group 637 (NOAA Active Region 4220) and SIDC Sunspot Group 642 (NOAA Active Region 4221) have exhibited notable flux emergence and growth, but have been mostly quiet. The solar flaring activity over the next 24 hours is expected to increase towards moderate levels with over 50% chances of isolated M-class flaring.

Coronal mass ejections

A weak slow (with an estimated projected velocity of around 300 km/s) partial halo coronal mass ejection (SIDC CME 558) was detected in LASCO/C2 data lifting off the solar surface around 04:00 UTC on Sept 16. The CME is related to a prominence eruption from behind the south- east limb and has no Earth-directed component. No Earth-directed 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 at L1) remained under the influence of a high speed stream associated with the negative polarity SIDC Coronal Hole 116. The solar wind speed reached a maximum value of 857 km/s. The magnitude of the interplanetary magnetic field, B, reached a maximum of 14.5 nT with a minimum Bz component of - 10.6 nT. The B field phi angle was predominantly in the negative sector (directed towards the Sun). The solar wind conditions are expected to continue to be elevated under the HSS influence over the day and start to return towards slow solar wind regime on Sept 18.

Geomagnetism

The geomagnetic conditions over the past 24 hours have globally at active to minor storm levels. Predominantly unsettled to active were registered locally over Belgium. The global geomagnetic conditions over the next 24 hours are expected to be at unsettled to minor storm levels with remaining chances for an isolated moderate storm. The geomagnetic conditions are expected to be predominantly at quite to unsettled levels on Sept 18 with possible 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 was at nominal levels and is expected to remain at nominal levels in the next 24 hours.

Today's estimated international sunspot number (ISN): 122, based on 14 stations.

Solar indices for 15 Sep 2025

Wolf number Catania	092
10cm solar flux	///
AK Chambon La Forêt	034
AK Wingst	039
Estimated Ap	038
Estimated international sunspot number	081 - 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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