Viewing archive of Friday, 26 September 2025

Daily bulletin on solar and geomagnetic activity from the SIDC

Issued: 2025 Sep 26 1231 UTC

SIDC Forecast

Solar flares

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

Geomagnetism

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

Solar protons

Quiet

	10cm flux	Ap
26 Sep 2025	166	006
27 Sep 2025	164	014
28 Sep 2025	163	020

Solar Active Regions and flaring

Solar flaring activity was moderate over the past 24 hours, with only C-class flares. The strongest flare was a C3.4 flare (SIDC Flare 5562) peaking at 14:01 UTC on September 25, which was associated with SIDC Sunspot Group 640 (NOAA Active Region 4217, magnetic type beta). There are currently nine numbered active regions on the solar disk. SIDC Sunspot Groups 592, 640, 648, 644, 650 (NOAA Active Regions 4226, 4217, 4230, 4224, 4229) are the most complex, all with magnetic type beta. SIDC Sunspot Group 642 (NOAA Active Region 4221) and SIDC Sunspot Group 647 have rotated over the west limb. The solar flaring activity is expected to be low over the next 24 hours, with C-class flares very likely and a chance for M-class flares.

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) are gradually returning to the slow solar wind regime, under the waning influence of the high-speed stream from the mid-latitude, negative polarity coronal hole (SIDC Coronal Hole 126). The solar wind speed decreased from approximately 500 km/s to approximately 430 km/s. The interplanetary magnetic field values were mostly around 5 nT. The Bz component varied between -4 nT and 5 nT. The interplanetary magnetic field angle was in the negative sector. Enhanced solar wind conditions are possible over the next 24 hours due to the high- speed stream associated with the small, equatorial, negative polarity coronal hole (SIDC Coronal Hole 132) that crossed the central meridian on September 24.

Geomagnetism

Geomagnetic conditions globally and locally were mostly at quiet to unsettled levels (NOAA Kp 1 to 3, K BEL 1 to 3). Unsettled to active conditions are possible over the next 24 hours due to the high-speed stream associated with the small, equatorial, negative polarity coronal hole (SIDC Coronal Hole 132) that crossed the central meridian on September 24.

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 and GOES 19 was below the 1000 pfu threshold in the last 24 hours. The greater than 2 MeV electron flux is expected to be below the 1000 pfu threshold over the next 24 hours. The 24-hour electron fluence is presently at normal levels and is expected to remain so over the next 24 hours.

Today's estimated international sunspot number (ISN): 154, based on 10 stations.

Solar indices for 25 Sep 2025

Wolf number Catania	186
10cm solar flux	170
AK Chambon La Forêt	018
AK Wingst	007
Estimated Ap	007
Estimated international sunspot number	155 - Based on 13 stations

Noticeable events summary

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

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