Viewing archive of Saturday, 24 April 2021

Daily bulletin on solar and geomagnetic activity from the SIDC

Issued: 2021 Apr 24 1230 UTC

SIDC Forecast

Solar flares

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

Geomagnetism

Quiet (A<20 and K<4)

Solar protons

Quiet

	10cm flux	Ap
24 Apr 2021	079	013
25 Apr 2021	077	011
26 Apr 2021	077	012

Bulletin

During last 24 hours solar flaring activity was at the B-class and C-class level. As expected majority of flares originated from the Catania sunspot group 87 (NOAA AR 2816) although Catania sunspot group 86 (NOAA AR 2817) was also source of flaring activity while rotating over the West solar limb. Catania sunspot group 89 (NOAA AR 2819) is approaching to the center of the solar disc and was also source of the flaring activity during last few hours. 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 above the 1000 pfu threshold until midnight of April 23. Its present value fluctuates around 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 in situ observations indicate the arrival of the solar wind originating from the small, negative polarity equatorial coronal hole (reached central meridian in the morning of April 20), starting from evening of April 23. The observed density increase was followed by the increase of the interplanetary magnetic field magnitude, solar wind temperature and speed with predominantly negative value of the phi angle. Presently the solar wind speed is about 490 km/s and the interplanetary magnetic field magnitude is about 4 nT. Fain and slow partial halo CME (first seen in the SOHO LASCO C2 field of view at about 06:12 UT on April 22) is expected at Earth on late evening of April 25. The arrival of solar wind from the coronal hole (with the Bz component of the interplanetary magnetic field as low as -8 nT) has induced active geomagnetic conditions yesterday evening. The local station at Dourbes reported Kp=5 (from about 23:00 UT on April 23 until 02:00 UT on April 24) and NOAA reported planetary index K=5 (from about 22:00 UT until midnight on April 23). The geomagnetic conditions are presently quiet. As the solar wind speed and interplanetary magnetic field magnitude already started to decrease we expect quite to unsettled geomagnetic conditions in the coming hours. The expected arrival of the CME might induce disturbed geomagnetic condition in the late evening of April 25.

Today's estimated international sunspot number (ISN): 056, based on 26 stations.

Solar indices for 23 Apr 2021

Wolf number Catania	///
10cm solar flux	077
AK Chambon La Forêt	029
AK Wingst	019
Estimated Ap	020
Estimated international sunspot number	034 - Based on 37 stations

Noticeable events summary

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

All times in UTC

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