Viewing archive of Saturday, 20 September 2025

Daily bulletin on solar and geomagnetic activity from the SIDC

Issued: 2025 Sep 20 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
20 Sep 2025	164	004
21 Sep 2025	166	014
22 Sep 2025	169	027

Solar Active Regions and flaring

Solar flaring activity over the past 24 hours has reached moderate levels with a registered M1.5 flare (SIDC Flare 5521) peaking at 21:41 UTC on Sept 19. The flare was produced by SIDC Sunspot Group 621 (NOAA Active Regions 4216, 4222), which has developed a beta-gamma configuration of its underlying magnetic field and has exhibited some decay. A total of 11 numbered sunspot groups were identified on the visible solar disk with two regions rotating from over the east limb. SIDC Sunspot Group 637 (NOAA Active Region 4220) has decreased its complexity and is currently classified as magnetic type beta-gamma. It remains the largest region on the visible disc followed by SIDC Sunspot Group 640 (NOAA Active Region 4217) and SIDC Sunspot Group 607 (NOAA Active Region 4225), both classified as magnetic type beta. Regardless of their size and the complexity of SIDC Sunspot Group 637, these regions have remained quiet and the flaring activity was dominated by SIDC Sunspot Group 621, SIDC Sunspot Group 642 (NOAA Active Region 4221) and SIDC Sunspot Group 643 (NOAA Active Region 4223). The latter regions has exhibited decay is currently classified as magnetic type alpha. The solar flaring activity over the next 24 hours is expected to be moderate levels over the next 24 hours, with likely further 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.

Coronal holes

A mid-latitude negative polarity coronal hole (SIDC Coronal Hole 126) which first crossed the central meridian on Sept 19 continues to reside there. A high speed stream emanating from this coronal hole is expected to reach the Earth possibly in the UTC afternoon of Sept 21.

Solar wind

Over the past 24 hours the solar wind parameters (as measured by ACE) were indicative of background slow solar wind conditions. The solar wind speed was mostly below 400 km/s. The magnitude of the interplanetary magnetic field, B, remained rather weak with a maximum of 4 nT and a minimum Bz component of - 3 nT. The B field phi angle remained 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 24 hours and registered enhancements thereafter with an expected high speed stream arrival associated with a negative polarity SIDC Coronal Hole 126.

Geomagnetism

The geomagnetic conditions over the past 24 hours were quiet. The geomagnetic conditions are expected to be predominantly quiet over the next 24 hours. Active conditions with possible minor storm levels might be reached later on Sept 21 and on Sep 22 with an expected high speed stream arrival.

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 been entirely above 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 24 to 48 hours, after which the electron fluence is expected to return to nominal levels.

Today's estimated international sunspot number (ISN): 161, based on 14 stations.

Solar indices for 19 Sep 2025

Wolf number Catania	///
10cm solar flux	160
AK Chambon La Forêt	007
AK Wingst	002
Estimated Ap	002
Estimated international sunspot number	147 - 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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