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Daily bulletin on solar and geomagnetic activity from the SIDC

Emesso: 2016 Apr 18 1230 UTC

SIDC Forecast

Brillamenti solari

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

Geomagnetism

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

Protoni solari

Warning condition (activity levels expected to increase, but no numeric forecast given)

	10cm flux	Ap
18 Apr 2016	105	018
19 Apr 2016	102	028
20 Apr 2016	099	010

Bulletin

Solar activity reached high levels with Catania group 54 (NOAA AR 2529, Eki, Beta-gamma) producing an M6.7 flare which peaked at 00:29UT. The region slightly increased in size while opposite flux cancellation was detected in the leading edge. The other region on disk (Catania group 59, NOAA AR 2532) was fairly insignificant, as was the small newly recorded group 58. Further C flaring (probability 75%) from Catania group 54 (NOAA AR 2529) is expected and another M flare remains possible (probability 25%). The M6 flare was associated with a type II radio burst and SoHO/LASCO C2 imagery shows the first appearance of an associated coronal mass ejection (CME) at 00:12UT. It's angular extent appears fairly restricted, around 110 degrees, and it is mainly directed towards the West. Also from Stereo A position the CME appears to be directed mainly off the Sun-Earth line. The measured projected speed is around 1000 km/s. Given its mainly Westward direction and limited angular extent we do not expect any direct influence at Earth. No other CME's were detected in coronagraph images. Some slight (still <10 pfu) and gradual increase in >10MeV protons can be seen in GOES measurements after 6:00UT, probably related to the M6 flare and CME onset. Should further large flaring from Catania group 54 (NOAA AR 2529) in the Western hemisphere occur, this would represent an increased probability for a proton event.

Solar wind conditions were elevated. Solar wind density and total magnetic field increased sharply around 18:00UT with total magnetic field reaching 13nT while solar wind speed remained around 400 km/s and was even slightly decreasing (with a minimum near 370 km/s). The Bz component remained pronounced positive during the period of enhanced field strength while the magnetic field phi angle showed gentle rotation from the negative towards the positive sector from 00:30UT to 08:00UT as the total magnetic field strength decreased steadily. Afterwards total magnetic field remained low (2-3nT) for some hours, with variable Bz and phi angle, before increasing to current values of total magnetic field of 6nT. An increase in solar wind temperature and a slight increase in solar wind speed to 390 km/s was also seen in the last hours. Hence we remain in anticipation of the expected arrival of a high speed stream from the positive polarity coronal hole on the Northern hemisphere. Geomagnetic conditions reached active levels in the first half of the reporting period (both local K Dourbes and NOAA Kp 4), while quiet to unsettled conditions were recorded today (both local K Dourbes and NOAA Kp 1-3). With the expected/possible arrival of the coronal hole high speed stream later today, active conditions may be expected in the next 24-48 hours.

Today's estimated international sunspot number (ISN): 032, based on 21 stations.

Solar indices for 17 Apr 2016

Wolf number Catania	///
10cm solar flux	102
AK Chambon La Forêt	022
AK Wingst	018
Estimated Ap	022
Estimated international sunspot number	037 - Based on 24 stations

Noticeable events summary

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

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