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Daily bulletin on solar and geomagnetic activity from the SIDC

Emesso: 2015 Sep 20 1230 UTC

SIDC Forecast

Brillamenti solari

M-class flares expected (probability >=50%)

Geomagnetism

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

Protoni solari

Quiet

	10cm flux	Ap
20 Sep 2015	110	029
21 Sep 2015	115	029
22 Sep 2015	115	017

Bulletin

A new active region (NOAA 2420) rounded the northeast limb and produced the strongest flare of the period, an M1.5 flare peaking at 05:03UT. Based on some scarce SOHO and STEREO-A coronagraph imagery, no coronal mass ejection (CME) seems to be associated to this event. The group's proximity to the limb currently hampers an accurate assessment of its magnetic configuration. The other sunspot regions were stable and relatively quiet, NOAA 2419 and NOAA 2415 producing resp. 1 and 2 low-level C-class flares.

C-class flares are expected, with a good chance on another M-class flare.

After the passing of the brief negative sector boundary ("toward" phi angle) on 19 September, solar wind speed gradually increased from about 400 km/s to 450 km/s early this morning. A shock in the solar wind speed was observed at 05:27UT, with an abrupt increase to 550 km/s. After that, solar wind speed oscillated between mostly 500 and 600 km/s. The source of the disturbance is most likely the earlier than expected arrival of the 18 September coronal mass ejection (CME). Bz initially turned sharply negative with values up to -18 nT. Since about 06:00UT Bz varies between +7 and -12 nT, being predominantly negative. This resulted in strong geomagnetic storming, with the planetary K-index reaching 7 (major storm) and the local K Dourbes at 5 (minor storm).

Quiet to active geomagnetic conditions are expected, with a good chance on another minor storming episode in the wake of the solar wind disturbance.

Today's estimated international sunspot number (ISN): 062, based on 22 stations.

Solar indices for 19 Sep 2015

Wolf number Catania	///
10cm solar flux	106
AK Chambon La Forêt	025
AK Wingst	016
Estimated Ap	017
Estimated international sunspot number	061 - Based on 21 stations

Noticeable events summary

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

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