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Daily bulletin on solar and geomagnetic activity from the SIDC

Emesso: 2025 May 31 1241 UTC

SIDC Forecast

Brillamenti solari

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

Geomagnetism

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

Protoni solari

Warning condition (activity levels expected to increase, but no numeric forecast given)

	10cm flux	Ap
31 May 2025	163	026
01 Jun 2025	167	031
02 Jun 2025	172	054

Solar Active Regions and flaring

Solar flaring activity was high over the past 24 hours with 4 M-class flares recorded. The largest flare was a long duration M8.1 flare (SIDC Flare 4506) peaking on May 31 at 00:05 UTC, which was produced by SIDC Sunspot Group 469 (NOAA Active Region 4100, magnetic type Beta-Gamma-Delta). This region was responsible for most of the flaring activity including two further M-class flares. Returning region SIDC Sunspot group 490 (NOAA Active region 4104) also produced an M1.6 flare (SIDC Flare 4498) peaking on May 30 at 18:39 UTC and multiple C-class flares. SIDC Sunspot group 508 (NOAA Active region 4099, magnetic type Beta-Delta) was stable. There were 7 numbered sunspot groups on the disk over the past 24 hours, the rest of these regions were simple and mostly quiet. The solar flaring activity is expected to be moderate over the next 24 hours, with M-class flares expected and a chance for X-class flares.

Espulsioni di massa coronale

A halo coronal mass ejection (CME) was first detected in SOHO/LASCO-C2 images from 01:36 on May 31. This CME was associated with a long duration M8.1 flare (SIDC Flare 4506) peaking on May 31 at 00:05 UTC, which was produced by SIDC Sunspot Group 469 (NOAA Active Region 4100). This event was associated with a Type II radio emission. The CME has an estimated speed of over 1300 km/s and is expected to be Earth directed. Analysis is ongoing for an estimated arrival time, but initial analysis suggests this could arrive at Earth from late on June 1. The CME first detected at 07:12 UTC May 30 is also expected to have a glancing blow at Earth on June 2 but may be caught up by the following faster halo CME.

Fori coronali

An extended polar to equatorial coronal hole (combined SIDC Coronal Hole 116 and 112) continues to transit the central meridian since May 26.

Vento solare

The solar wind conditions reflected the ongoing impact of the high-speed stream associated with the large equatorial coronal hole that first began to cross the central meridian on May 26. The solar wind speed gradually decreased from 800 km/s to 660 km/s. The interplanetary magnetic field ranged between 5 and 7 nT. Bz ranged between -6 nT and 5nT. The interplanetary magnetic field phi angle was mostly in the negative sector. Further enhanced solar wind conditions are expected over the next 24 hours due to the ongoing high-speed stream and from the possible arrival of two CMEs from late on June 1.

Geomagnetism

Geomagnetic conditions reached active storm levels globally (Kp 4). This is due to the ongoing high-speed stream associated with the negative polarity coronal hole that began crossing the central meridian on May 26 (SIDC Coronal Hole 116 and 112). Locally, only moderate storm conditions were observed (K Bel 5). The conditions then reduced and are at unsettled to active levels at the end of the period. Active to minor storm conditions expected to continue over the next 24 hours, with isolated periods of moderate storm conditions possible, due to the ongoing impact of the high-speed stream.

Proton flux levels

The greater than 10 MeV proton flux increases slightly around 09:30 UTC May 31 but remained below the 10 pfu threshold over the past 24 hours. It is expected to remain below this threshold level over the next 24 hours. A chance of an increase remains due to any high-level flaring activity, particularly from SIDC Sunspot Group 469 (NOAA Active Region 4100.

Electron fluxes at geostationary orbit

The greater than 2 MeV electron flux measured by GOES 18 and 19 was above the 1000 pfu threshold. The greater than 2 MeV electron flux is expected to again exceed the 1000 pfu threshold over the next 24 hours. The 24-hour electron fluence was at moderate levels and is expected to be at moderate to high levels over the next 24 hours.

Today's estimated international sunspot number (ISN): 127, based on 20 stations.

Solar indices for 30 May 2025

Wolf number Catania	120
10cm solar flux	157
AK Chambon La Forêt	035
AK Wingst	///
Estimated Ap	028
Estimated international sunspot number	127 - Based on 27 stations

Noticeable events summary

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

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