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Daily bulletin on solar and geomagnetic activity from the SIDC

Emesso: 2021 Apr 27 1235 UTC

SIDC Forecast

Brillamenti solari

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

Geomagnetism

Quiet (A<20 and K<4)

Protoni solari

Quiet

	10cm flux	Ap
27 Apr 2021	080	011
28 Apr 2021	079	007
29 Apr 2021	079	007

Bulletin

X-ray flux remained below C level during the period. Catania group 91 (NOAA region 2821) and Catania group 92 (NOAA region 2820) grew but remained quiet. These two regions remain the most prominent regions on disc and are a likely source for C-class flaring with a slight chance for an M-class flare.

A long filament stretching across the central meridian in the Southern hemisphere erupted as seen in SDO/AIA 304 images from around 13:00UT. An associated Westward (from STEREO A perspective) CME is seen from around 20:24 in STEREO A COR2 images. In (incomplete) SoHO/LASCO coronagraph images so far only a weak Southward signature is seen around 23:12 UT. Given the location of the filament and the direction as seen in STEREO A COR2 a possible Earth directed component or a glancing blow is possible. The CME speed is estimated to be again slow and a possible arrival may not be distinguishable from the arrival of the CME from April 25 which may be expected around April 31/May 1. Updates will be provided when more data become available.

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.

A patchy coronal hole region in the northern hemisphere is started cross the central meridian. It may influence Solar wind starting from May 1 onwards.

Solar wind remained enhanced with the lasting passage of the April 22 CME. Solar wind speed reached just over 500 km/s again during the period but seems now to be reducing towards 450 km/s. The magnetic field was at around 5nT with a phi angle indicating magnetic field orientation mostly towards the Sun. Solar wind conditions are expected to return to slow solar wind conditions. By end of April 31, start of May 1 we may see solar wind perturbations by a combination of enhanced speed associated to the coronal hole currently transiting the central meridian, and magnetic field perturbations due to passing magnetic clouds from the April 25 and 26 CMEs.

Geomagnetic conditions were quiet to unsettled (local K Dourbes 0-3 and NOAA Kp 1-3). Geomagnetic conditions are expected to be quiet to unsettled.

Today's estimated international sunspot number (ISN): 053, based on 23 stations.

Solar indices for 26 Apr 2021

Wolf number Catania	077
10cm solar flux	080
AK Chambon La Forêt	014
AK Wingst	015
Estimated Ap	015
Estimated international sunspot number	048 - Based on 31 stations

Noticeable events summary

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

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