An active region currently positioned behind the northeast limb erupted with two M-class solar flares by 10:19 UTC on December 21, 2015. The first event started at 00:52, peaked at 01:03 as M2.8 and ended at 01:11 UTC. The second event started at 10:09, peaked at 10:19 as M1.1 and ended at 10:32 UTC.
This region was also responsible for several C-class solar flares. It will rotate into Earth view and be named during the next couple of days.
A Type II radio sweep with estimated velocity of 732 km/s and associated CME, first visible in coronagraph imagery at 01:26 UTC, accompanied the M2.8 flare. However, the event is far-sided and well off the Sun-Earth line.
SWPC forecasters expect the solar activity to be at low levels with a chance for M-class flares (R1-R2/Minor-Moderate radio blackouts) by December 23.
Meanwhile, the solar wind parameters, measured at the ACE satellite, reflected an enhanced solar wind environment as a result of the December 16 CME arrival late on December 19. Total field strength (Bt) remained elevated and ranged between 8-18 nT. The Bz component remained south and reached extended periods at deflections of -16 to -18 nT. After 10:30 UTC on December 21, Bz finally switched to a northward orientation.
Solar wind speed mostly ranged from 400 – 420 km/s and decreased to near 370 km/s by 12:30 UTC on December 21. The phi was predominantly in a negative (toward the sun) orientation.
Solar wind parameters are expected to slowly diminish by late on December 21 and continue to diminish on December 22 and 23 as CME effects wane.
The geomagnetic field was at active to G2 Moderate geomagnetic storm levels due to an enhanced interplanetary magnetic field as a result of the arrival of the CME from December 16.
Featured image credit: NASA / SDO AIA 131
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