Viewing archive of Wednesday, 17 December 2025

Daily bulletin on solar and geomagnetic activity from the SIDC

Issued: 2025 Dec 17 1231 UTC

SIDC Forecast

Solar flares

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

Geomagnetism

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

Solar protons

Quiet

	10cm flux	Ap
17 Dec 2025	115	012
18 Dec 2025	116	017
19 Dec 2025	115	008

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 C1.9 flare (SIDC Flare 6439) from beyond the east limb, peaking at 13:51 UTC on December 16. There are currently five numbered active regions on the solar disk. The most complex ones have a beta magnetic type. SIDC Sunspot Group 727 (NOAA Active Region 4309) and SIDC Sunspot Group 725 have decayed into plage. The solar flaring activity is expected to be low over the next 24 hours, with C-class flares very likely.

Coronal mass ejections

A Coronal Mass Ejection (SIDC CME 611) was observed in STEREO-A/COR2 coronagraph imagery, lifting off around 03:00 UTC on December 17. It is a backsided event 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 a high-speed stream from the northern, negative polarity coronal hole (SIDC Coronal Hole 142) and possibly the early arrival 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 4 nT and 10 nT. The Bz component was between -6 nT and 6 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 stream from SIDC Coronal Holes 136 and 137.

Geomagnetism

Geomagnetic conditions globally were mostly at unsettled levels (NOAA Kp 3 to 3+ ) during the last 24 hours. Geomagnetic conditions locally were quiet to unsettled (K Bel 2 to 3) during the last 24 hours. Unsettled to active conditions (NOAA Kp 3 to 4), with a small chance of isolated periods of minor storm conditions (NOAA Kp 5), 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 close to the 1000 pfu threshold but remained mostly below it during the last 24 hours. It 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): 078, based on 05 stations.

Solar indices for 16 Dec 2025

Wolf number Catania	///
10cm solar flux	117
AK Chambon La Forêt	020
AK Wingst	012
Estimated Ap	012
Estimated international sunspot number	073 - Based on 13 stations

Noticeable events summary

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

All times in UTC

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