After several days of pent-up quiet, big sunspot AR2473 erupted on Dec. 28 (12:49 UT), producing a slow but powerful M1.9-class solar flare. NASA's Solar Dynamics Observatory recorded the blast's extreme ultraviolet glow. For more than an hour, UV radiation from the flare bathed the top of Earth's atmosphere, ionizing atoms and molecules. This, in turn, disrupted the normal propagation of shortwave radio signals on the dayside of our planet.
A NOAA blackout map shows the affected area. Ham radio operators, mariners and aviators in South America, Africa and the south Atlantic Ocean may have noticed fades and blackouts of transmissions below 20 MHz.
The slow explosion also produced a coronal mass ejection (CME). Images from the Solar and Heliospheric Obseratory (SOHO) show a ragged, full-halo CME heading almost directly toward Earth.
NOAA analysts have modeled this CME, and they say it could reach Earth as early as Dec. 30, with a 60% chance of polar geomagnetic storms when the CME arrives. The CME impact may cause a sudden impulse geomagnetic response at Earth, likely resulting in the G3 (strong) conditions.
Sunspot AR2473 has an unstable 'beta-delta' magnetic field that could explode again in the hours ahead. NOAA forecasters estimate a 50% chance of additional M-class flares and a 10% chance of X-flares on Dec. 29.
There is a continued chance for (R1-R2/Minor-Moderate) radio blackouts over the next three days (Dec. 29-31). Satellite systems may experience significant charging resulting in increased risk to satellite systems. Aurora may be seen as low as New York to Wisconsin to Washington state.