Viewing archive of Wednesday, 22 April 2015

Daily bulletin on solar and geomagnetic activity from the SIDC

Issued: 2015 Apr 22 1230 UTC

SIDC Forecast

Solar flares

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

Geomagnetism

Minor storm expected (A>=30 or K=5)

Solar protons

Quiet

	10cm flux	Ap
22 Apr 2015	154	031
23 Apr 2015	155	035
24 Apr 2015	156	007

Bulletin

Solar X-ray flaring activity reached moderate levels with a total of 5 M flares, for which Catania group 28 (NOAA 2322) on the west limb was the most significant contributor. The largest flare was an M4.0 flare peaking at 15:45UT followed by an M2.1 flare peaking at 17:00UT, both from Catania group 28 (NOAA 2322). Later, in the decay phase of another M1.8 flare from that region peaking at 21:45UT a secondary peak of M1.2 magnitude at 22:01 UT is hard to attribute to any specific region. Finally, the region caused another M1.1 flare peaking at 8:44UT this morning. Some further C flaring was observed mainly from Catania groups 32, 33 and 38 (respectively NOAA 2324, 2325 and 2327). The region on the eastern limb (now numbered Catania 44) which was the source of M flaring yesterday, remained remarkably silent today (apart from the eruptions described below). Field separation was observed in Catania group 37 (newly numbered NOAA 2331), as well as slight growth in Catania group 36 (newly numbered NOAA 2332) and Catania 38 (NOAA 2327). All other existing groups appeared stable or in decay. A number (6 in total) of additional small sunspot groups were numbered by Catania (39-43). With Catania group 28 departing behind the western limb, the most important source of M flaring is disappearing. Catania group 44 at the East limb still deserves to be monitored closely despite remaining quiet in the past 24 hours. Hence C flaring is expected with a chance for M flaring remaining over the next days. Proton levels were at background values. An partial (asymmetric full) halo with primary north-east direction is visible in SoHO/LASCO C2 coronagraph images from 10:36 UT April 21 onwards. The event actually comprises of three consecutive events. At 10:25UT SDO/AIA images show a darkening at the north-east limb. The opening fieldlines appear to be originating from behind the limb. The consecutive post-flare arcades are visible at the limb and are the source of the M2.2 flare with peak time 10:40UT reported earlier. At 11:48 the SoHO/LASCO C2 coronagraph images show a second CME departing the west limb, again with no clearly identifiable on disc source although it appears to coincide with (though slightly preceding) the M2.2 flare observed from Catania group 28 (NOAA region 2322) close to the West limb. This second event is much less powerful than the first but could add to the apparent angular width. Following the M2.2 flare at the north-east limb, a third eruption is visible in the coronagraph data from 13:36 UT onwards. The eruption is also clearly visible in SDO/AIA 304 images, showing it to originate from the visible side of the Sun, although very close to the limb. This third CME appears as fairly narrow in the coronagraph images. All in all, given the location of origin of the CME's, none of these events is expected to have any influence at Earth location. Solar wind parameters show a continuing influence of the positive polarity coronal hole high speed stream, without clear indication of any possible arrival of the April 18 CME. Solar wind speed remained stable at around 540-580 km/s. Total magnetic field decreased from mainly around 6 nT at the start of the period to around 4 nT currently. Magnetic field phi angle was stable in the outward sector and Bz was variable in the -5 to +6 nT range. Geomagnetic conditions were quiet to active (both NOAA Kp and local K Dourbes 2-4). In the next 24 hours we should see the declining influence of the high speed stream, with possibly further agitated conditions due to the arrival of the April 18 CME. Associated quiet to minor geomagnetic storm conditions should be expected.

Today's estimated international sunspot number (ISN): 102, based on 19 stations.

Solar indices for 21 Apr 2015

Wolf number Catania	136
10cm solar flux	154
AK Chambon La Forêt	026
AK Wingst	022
Estimated Ap	023
Estimated international sunspot number	096 - Based on 30 stations

Noticeable events summary

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

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