Viewing archive of Sunday, 25 April 2021

Daily bulletin on solar and geomagnetic activity from the SIDC

Issued: 2021 Apr 25 1241 UTC

SIDC Forecast

Solar flares

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

Geomagnetism

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

Solar protons

Quiet

	10cm flux	Ap
25 Apr 2021	079	019
26 Apr 2021	080	011
27 Apr 2021	081	006

Bulletin

Number of B-class and one C-class flares were reported during last 24 hours. Majority of the flaring activity originated from the Catania sunspot group 89 (NOAA AR 2820). The C2.6 flare (peaked at 01:35 UT on April 25) originated from the Catania sunspot group 87 (NOAA AR 2816). The flare was associated with the EUV wave, coronal dimmings and rather narrow CME as seen in the available SOHO/LASCO C2 and STEREO/COR2 observations. We expect the present level of the solar flaring activity to persist in the coming hours. We expect B-class and C-class flares while M-class flares are, although possible, not very probable. There were no Earth directed CMEs observed during last 24 hours and the proton flux levels remained at background values.

The greater than 2MeV electron flux was most of the time above the 1000 pfu threshold, and it is expected to stay so in the coming hours. The 24h electron fluence is at moderate level and is likely it will stay so in the next 24 hours.

The solar wind speed is presently about 480 km/s and the interplanetary magnetic field magnitude is about 7 nT. The in situ observations show arrival of the shock wave at about 22:27 UT on April 24. The sudden increase of the interplanetary magnetic field strength (from 5 to 10 nT), was simultaneous with the density, solar wind velocity and temperature increase. The shock wave was driven by the partial halo CME first seen in the SOHO LASCO C2 field of view at about 06:12 UT on April 22. The CME was associated with C3.8 flare (peaked at 04:35 UT) that originated from the Catania sunspot group 87 (NOAA AR 2816) at that moment situated at the center of the solar disc. The CME arrived to Earth about half a day earlier then expected. This discrepancy is possibly due to uncertainty in the estimation of the halo and partial halo CME speeds. Arrival of the shock wave induced disturbed geomagnetic conditions (Kp=4 and K=5, reported by Dourbes and NOAA respectively) from about midnight until 04 UT this morning. The geomagnetic conditions are presently unsettled to quiet and we expect them to stay so in the coming hours.

Today's estimated international sunspot number (ISN): 053, based on 20 stations.

Solar indices for 24 Apr 2021

Wolf number Catania	///
10cm solar flux	079
AK Chambon La Forêt	023
AK Wingst	008
Estimated Ap	008
Estimated international sunspot number	055 - Based on 32 stations

Noticeable events summary

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

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