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Daily bulletin on solar and geomagnetic activity from the SIDC

Emesso: 2026 May 31 1231 UTC

SIDC Forecast

Brillamenti solari

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

Geomagnetism

Quiet (A<20 and K<4)

Protoni solari

Quiet

	10cm flux	Ap
31 May 2026	140	008
01 Jun 2026	138	010
02 Jun 2026	136	010

Solar Active Regions and flaring

Solar flaring activity has been low over the last 24 hours, with a few C-class flares. The strongest flare was a C3.1 flare (SIDC Flare 7810) peaking at 02:09 UTC on May 31, associated with SIDC Sunspot Group 873 (NOAA Active Region 4446, magnetic type beta). There are currently nine numbered active regions on the solar disk. The most complex ones have a beta magnetic type. SIDC Sunspot Groups 805, 862, 874 and 876 (NOAA Active Regions 4445, 4443, 4448 and 4451) have decayed into plage. The solar flaring activity is expected to be low over the next 24 hours, with C-class flares very likely and a small chance for M-class flares.

Espulsioni di massa coronale

A narrow Coronal Mass Ejection (SIDC CME 663) was observed in LASCO/C2 and STEREO-A coronagraph imagery, lifting off from the northeast limb, starting from 07:30 UTC on May 31. It is associated with a prominence eruption observed in AIA 304 data around 05:00 UTC on May 31 over the northeast limb. It is not expected to impact Earth. No other Earth-directed CMEs were observed in the available coronagraph imagery during the last 24 hours.

Fori coronali

An equatorial, positive polarity coronal hole (SIDC Coronal Hole 166) is crossing the central meridian. An associated high-speed stream may arrive at Earth starting from the UTC morning on June 03.

Vento solare

Over the last 24 hours, the solar wind parameters (ACE and DSCOVR) were enhanced, likely due to the ongoing influence of high-speed streams from the two negative polarity coronal holes (the northern SIDC Coronal Hole 142 and the equatorial SIDC Coronal Hole 165, which crossed the central meridian on May 27 and May 28 respectively). The solar wind speed increased from 400 km/s to 560 km/s. The interplanetary magnetic field decreased from 11 nT to around 5 nT. The Bz component varied between -10 nT and 5 nT. The interplanetary magnetic field angle phi was predominantly in the negative sector. Over the next 24 hours, enhanced solar wind conditions may still be observed initially, followed by a gradual return to the slow solar wind regime.

Geomagnetism

Geomagnetic conditions globally were initially quiet (NOAA Kp 2) and then reached active levels (NOAA Kp 3- to 4+ ) between 18:00 UTC on May 30 and 03:00 UTC on May 31. Geomagnetic conditions locally were initially quiet to unsettled (K Bel 2 to 3), reaching active levels between 18:00 UTC and 22:00 UTC on May 30. Mostly quiet conditions, with possible isolated intervals of unsettled or active conditions, are expected over the next 24 hours.

Proton flux levels

The greater than 10 MeV proton flux was below the 10 pfu threshold during the last 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 elevated but remained below the 1000 pfu threshold during the last 24 hours. The 24-hour electron fluence was at normal levels and it is expected to remain so over the next 24 hours.

Today's estimated international sunspot number (ISN): 120, based on 12 stations.

Solar indices for 30 May 2026

Wolf number Catania	///
10cm solar flux	142
AK Chambon La Forêt	030
AK Wingst	016
Estimated Ap	017
Estimated international sunspot number	133 - Based on 27 stations

Noticeable events summary

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

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