FAST WARNING 'PRESTO' MESSAGE  from the SIDC (RWC-Belgium) 2014 Apr 20
14:47:53

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.