The Sun Online and solar activity. April 20, 2014

Twelve active regions were reported by NOAA today. Three of them (NOAA ARs 2034, 2035, and 2036) have beta-gamma configuration of the photospheric magnetic field. These three active regions and four others were responsible for numerous C-class flares yesterday and today. None of them was associated with an Earth-directed CME. The strongest flare of the past 24 hours was the C6.4 flare peaking at  08:13 UT today in the NOAA AR 2032 at the west solar limb. We expect further flaring activity on the C-level,
with a good chance for an M-class event. An interplanetary shock-like structure was detected this morning. ACE recorded jumps of solar wind speed, temperature, and the interplanetary magnetic filed (IMF) magnitude at 10:23 UT. SOHO/CELIAS detected a jump in density at 10:22 UT, but the jump in speed was detected only 20 to 30 minutes later. Therefore, this discontinuity does not seem to be a typical ICME-driven fast forward shock as ACE did not detect a jump in density at all, and jumps in density and
the solar wind speed detected by SOHO/CELIAS were not simultaneous. There is, however, very little doubt that this is a start of an ICME corresponding to the halo CME observed on the Sun on April 18. During the intervals of the strongest IMF magnitude in the post-shock solar wind flow (up to 22 nT), the north-south IMF component Bz was either northward or close to zero. Unsettled geomagnetic conditions (K = 3) were reported by Dourbes and NOAA, and active conditions (K = 4) were reported by IZMIRAN.
Currently the IMF magnitude is around 12 nT and the solar wind speed is around 650 km/s, so minor geomagnetic storm conditions (K = 5) are still possible. After the arrival of the shock-like structure, the proton flux at energies above 10 MeV decreased to values below the threshold of the proton event. The proton flux, however, remains high, and in case of another solar eruption with associated SEPs, the event threshold could be easily crossed. We therefore issue a warning condition for a proton event.

Equipment: Coronado 90 +  Imaging Source DMK  + LX75
Processing: Photoshop, Avistack 300 frames
Date: 04/20/14
Time UT: 19:00
Exposure 1/182 sec.

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