Daily bulletin on solar and geomagnetic activity from the SIDC

Issued: 2025 Dec 18 1231 UTC

SIDC Forecast

Solar flares

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

Geomagnetism

Quiet (A<20 and K<4)

Solar protons

Quiet

	10cm flux	Ap
18 Dec 2025	119	014
19 Dec 2025	118	008
20 Dec 2025	117	007

Solar Active Regions and flaring

Solar flaring activity during the last 24 hours has been low, with only a few C-class flares. The strongest flare was a C3.2 flare (SIDC Flare 6445), peaking at 07:50 UTC on December 18. There are currently seven numbered active regions on the solar disk. The most complex ones have a beta magnetic type. SIDC Sunspot Groups 720 and 722 (NOAA Active Regions 4305 and 4307) are currently rotating across the west limb. SIDC Sunspot Group 703 (magnetic type alpha) has rotated on disk from the east limb, in the northeast quadrant. SIDC Sunspot Group 730 (magnetic type beta) has emerged in the southeast quadrant. The solar flaring activity is expected to be low over the next 24 hours, with C-class flares very likely.

Coronal mass ejections

A slow Coronal Mass Ejection (SIDC CME 612) was observed in LASCO/C2 and STEREO-A/COR2 coronagraph imagery, lifting off around 04:00 UTC on December 18. It is likely associated with a prominence eruption in the southwest limb and it is not expected to impact Earth. No other Earth-directed CMEs were observed in the available coronagraph imagery over the last 24 hours.

Solar wind

The solar wind conditions (ACE) during the last 24 hours were enhanced, likely under the ongoing influence of high-speed streams from the north-south elongated, negative polarity coronal hole (SIDC Coronal Hole 136) and the southern, negative polarity coronal hole (SIDC Coronal Hole 137). The solar wind speed increased from 600 km/s to around 710 km/s. The interplanetary magnetic field values ranged between 3 nT and 8 nT. The Bz component was between -7 nT and 4 nT. The interplanetary magnetic field angle phi was mostly negative. Enhanced solar wind conditions are expected over the next 24 hours, under the ongoing influence of the high-speed streams from SIDC Coronal Holes 136 and 137.

Geomagnetism

Geomagnetic conditions globally reached minor storm levels (NOAA Kp 5- ) between 21:00 UTC on December 17 and 00:00 UTC on December 18. Geomagnetic conditions locally reached active levels (K Bel 4) between 20:00 UTC on December 17 and 00:00 UTC on December 18. Unsettled to active conditions are expected over the next 24 hours, under the ongoing influence of the high-speed streams from SIDC Coronal Holes 136 and 137.

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 was above the 1000 pfu threshold between 17:00 UTC and 22:15 UTC on December 17. The greater than 2 MeV electron flux measured by GOES 19 was above the 1000 pfu threshold between 13:45 UTC and 16:45 UTC on December 17. The greater than 2 MeV electron flux is expected to remain mostly 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): 063, based on 07 stations.

Solar indices for 17 Dec 2025

Wolf number Catania	086
10cm solar flux	119
AK Chambon La Forêt	032
AK Wingst	021
Estimated Ap	020
Estimated international sunspot number	078 - Based on 14 stations

Noticeable events summary

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