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Daily bulletin on solar and geomagnetic activity from the SIDC

Emesso: 2025 Sep 21 1246 UTC

SIDC Forecast

Brillamenti solari

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

Geomagnetism

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

Protoni solari

Quiet

	10cm flux	Ap
21 Sep 2025	169	017
22 Sep 2025	172	024
23 Sep 2025	175	013

Solar Active Regions and flaring

Solar flaring activity over the past 24 hours was at low levels with only low C-class flares identified. A total of 11 numbered sunspot groups were identified on the visible solar disk. Most of the flaring activity over the past 24 hours was produced by SIDC Sunspot Group 637 (NOAA Active Region 4220), including a C3.4 flare (SIDC Flare 5529) with peak time at 20:11 UTC on Sept 20. This region, classified as magnetic type beta-gamma, remained the largest region on the visible solar disc currently located in the south-west quadrant at S18W46. SIDC Sunspot Group 607 (NOAA Active Region 4225) has been classified as magnetic type beta-delta, but has remained quiet. SIDC Sunspot Group 640 (NOAA Active Region 4217), also classified as magnetic type beta-delta, has produced some isolated low C-class flaring together with a returning region SIDC Sunspot Group 592 (NOAA Active Region 4226), currently classified as magnetic type beta. Some low levels of activity have been registered from another returning region (SIDC Sunspot Group 617) near the east limb. The solar flaring activity over the next 24 hours is expected to be at low to moderate levels over the next 24 hours, with likely isolated M-class flaring.

Espulsioni di massa coronale

No Earth-directed coronal mass ejections (CMEs) have been identified in the available coronagraph imagery over the past 24 hours.

Fori coronali

The mid-latitude negative polarity SIDC Coronal Hole 126 has now crossed the central meridian. A high speed stream related to it is expected to arrive to Earth later on Sept 21 or on Sept 22.

Vento solare

Over the past 24 hours the solar wind parameters (as measured by ACE) were at nominal slow solar wind levels. The solar wind speed mildly varied in the range of 310 km/s to 364 km/s. The magnitude of the interplanetary magnetic field, B, peaked at 6.5 nT with a minimum Bz component of - 2.7 nT. The B field phi angle was predominantly in the negative sector (directed towards the Sun). The solar wind conditions are expected to registered enhancements later on Sept 21 and Sept 22 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 over the next 24 hours are expected to range from quiet to minor storms levels due to an anticipated high speed stream arrival. Quiet to active conditions are expected for Sep 22 with possible isolated minor storms. Predominantly quiet to unsettled conditions are expected for Sept 23 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 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. It is expected to remain at moderate levels over the next 24 hours and decrease towards nominal levels after.

Today's estimated international sunspot number (ISN): 166, based on 11 stations.

Solar indices for 20 Sep 2025

Wolf number Catania	///
10cm solar flux	166
AK Chambon La Forêt	006
AK Wingst	004
Estimated Ap	004
Estimated international sunspot number	167 - Based on 23 stations

Noticeable events summary

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

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