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Daily bulletin on solar and geomagnetic activity from the SIDC

Emesso: 2021 Apr 26 1241 UTC

SIDC Forecast

Brillamenti solari

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

Geomagnetism

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

Protoni solari

Quiet

	10cm flux	Ap
26 Apr 2021	079	007
27 Apr 2021	078	007
28 Apr 2021	078	007

Bulletin

Catania group 92 (NOAA region 2820) released several B flares over the period, but the largest flare was a C1.3 flare peaking at 2:30 from NOAA region 2816 which meanwhile decayed into plage. A new bipolar sunspot group (Catania group 91; NOAA region 2821) emerged just to the west of Catania group 92 (NOAA region 2820). NOAA region 2819 (Catania group 90) is losing its spots and decaying into plage. Flaring at C level is quite likely (mostly from Catania group 92; NOAA region 2820) with only a slight chance for an M flare.

SoHO/LASCO C2 coronagraph data show first a East-bound CME from around 13:36UT. It is related to a filament eruption from the South-Eastern quadrant. In SDO/AIA 193, the filament can be seen to be starting to lift of slowly from around 6UT. The resulting signatures in SDO/AIA 193 and 171 are nicely visible from around noon April 25. This CME will not have any impact on Earth. On the Western side there are also CME signatures visible which are somewhat difficult to describe clearly. In STEREO COR2 images a much clearer view is obtained with a CME directed clearly towards the West (from STEREO perspective). The CME is slow from both perspectives and onset times are not clearly delineated but are around 18UT April 25. The ejecta are expected to be associated with field reconfiguration to the South-West of the newly emerged region NOAA 2820, where also dimmings can be seen around this time. All in all, the combined perspective seems to indicate that it is not excluded that some of the ejected material may be directed towards Earth. If it reaches Earth it should be expected around midnight April 30/May 1.

The greater than 10 MeV proton flux was at nominal levels over the past 24 hours and is expected to remain so for the next 24 hours. The greater than 2 MeV electron flux remained under the 1000 pfu event threshold. The 24h electron fluence was at normal levels and is expected to be at normal levels during next days.

Solar wind parameters showed the continued CME passage. Solar wind speed was 450-510km/s. The interplanetary field reached up to 8nT with this morning a 6-7h long period of persistently negative Bz down to -7.5nT. Solar wind conditions are expected to slowly return to slow solar wind conditions as the CME passes. If any of the ejecta from yesterday reach Earth this should be expected around midnight April 30/May 1. While this is not expected to enhance solar wind speed, the embedded magnetic field may still produce some geomagnetic impact.

Geomagnetic conditions reached minor storm levels (local K Dourbes and NOAA Kp 5) associated to the period of persistently Southward solar wind magnetic field. Geomagnetic conditions could still see some isolated active periods in the next 24h but are then expected to become quiet to unsettled.

Today's estimated international sunspot number (ISN): 047, based on 25 stations.

Solar indices for 25 Apr 2021

Wolf number Catania	///
10cm solar flux	079
AK Chambon La Forêt	021
AK Wingst	018
Estimated Ap	019
Estimated international sunspot number	050 - Based on 35 stations

Noticeable events summary

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

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