AURORAS LIKELY THIS WEEK: 2015 could end with an outburst of auroras. NOAA forecasters say there is a 60% chance of polar geomagnetic storms on Dec. 30th when a CME (described below) is expected to hit Earth's magnetic field. There is an equal 60% chance that the storms will spill over into Dec. 31st, New Year's Eve. Aurora alerts: text or voice
SUNSPOT ERUPTS, HURLS CME TOWARD EARTH: After several days of pent-up quiet, big sunspot AR2473 erupted on Dec. 28th (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: