Viewing archive of Sunday, 28 September 2025

Daily bulletin on solar and geomagnetic activity from the SIDC

Issued: 2025 Sep 28 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
28 Sep 2025	166	013
29 Sep 2025	165	005
30 Sep 2025	163	007

Solar Active Regions and flaring

Solar flaring activity was moderate over the past 24 hours, with one M-class flare. The strongest flare was a M6.4 flare (SIDC Flare 5601) peaking at 08:43 UTC on September 28, which was associated with SIDC Sunspot Group 653 (NOAA Active Region 4232, magnetic type beta-gamma). There are currently ten numbered active regions on the solar disk. Sunspot Group 653 (NOAA Active Region 4232) is the most complex. SIDC Sunspot Groups 650, 651 (NOAA Active Regions 4229, 4231) have rotated over the west limb. SIDC Sunspot Group 655 (NOAA Active Region 4234, magnetic type alpha) has emerged in the southeast quadrant. SIDC Sunspot Group 656 (NOAA Active Region 4235, magnetic type beta) and SIDC Sunspot Group 657 have emerged in the northeast quadrant. Sunspot Group 654 decayed into a plage region. The solar flaring activity is expected to be moderate over the next 24 hours, with C-class flares expected and M-class flares likely.

Coronal mass ejections

No Earth-directed Coronal Mass Ejections (CMEs) were observed in the available coronagraph imagery in the last 24 hours.

Solar wind

The solar wind conditions (ACE) initially reflected slow solar wind conditions and then showed a mild enhancement, possibly due to the high-speed stream associated with the small, equatorial, negative polarity coronal hole (SIDC Coronal Hole 133) that crossed the central meridian on September 25. Speed values increased from approximately 350 km/s to approximately 440 km/s. The interplanetary magnetic field values increased from 5 nT to 11 nT. The Bz component varied between -8 nT and 11 nT. The interplanetary magnetic field angle was mostly in the negative sector. Slow solar wind conditions are expected over the next 24 hours.

Geomagnetism

Geomagnetic conditions globally and locally were mostly at quiet to unsettled levels (NOAA Kp 1 to 3, K BEL 1 to 3). Mostly quiet conditions, with possible unsettled intervals, are expected globally and locally over the next 24 hours.

Proton flux levels

The greater than 10 MeV proton flux was below the 10 pfu threshold level over the past 24 hours. It is expected to remain below the threshold level over the next 24 hours.

Electron fluxes at geostationary orbit

The greater than 2 MeV electron flux measured by GOES 18 exceeded the 1000 pfu threshold between 16:00 UTC and 22:00 UTC on September 27 and remained below the threshold for the rest of the last 24 hours. The greater than 2 MeV electron flux measured by GOES 19 was over the 1000 pfu threshold until 20:00 UTC on September 27. The greater than 2 MeV electron flux is expected to be below the 1000 pfu threshold levels in the next 24 hours. The 24-hour electron fluence was mostly at normal levels and is expected to remain so over the next 24 hours.

Today's estimated international sunspot number (ISN): 164, based on 17 stations.

Solar indices for 27 Sep 2025

Wolf number Catania	///
10cm solar flux	164
AK Chambon La Forêt	015
AK Wingst	006
Estimated Ap	005
Estimated international sunspot number	143 - Based on 18 stations

Noticeable events summary

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

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