Aurora hopes dashed by weaker-than-expected solar storm
Posted December 9, 2020 1:36 p.m. EST
Updated December 10, 2020 2:50 p.m. EST
The northern horizon in North Carolina and Virginia west to Northern California is forecasted to take on a green color as particles from a solar storm interact with the upper atmosphere.
2 p.m. update
Following analysis of the initial shock as it passed NASA's Deep Space Climate Observatory (DSCOVR) approximately 1 million miles from Earth Wednesday night at 8:32 p.m. ET, NOAA's Space Weather Prediction Center has downgraded their forecast for the intensity of the geomagnetic storm.
The energy detected there less than needed to produce a G3 (strong) geomagnetic storm, therefore not strong enough to push auroral activity far enough south for it to be visible from North Carolina and Virginia. A G1 (minor) storm is expected instead which could produce auroras tonight but will be visible further north like Alaska, northern Canada and Europe
Even had the storm been stronger, we won't see the spectacular ribbons of color you may have seen in photos. North Carolina would see just a faint green hue in the sky This is happening in the upper atmosphere over the US/Canada border. At the horizon, we are looking through more than 30 times the amount of atmosphere directly above.
Our Sun occasionally burps, in the form of a surface eruption that sends super heated gas along with a few billion tons of material out into space. A coronal mass ejections (CME) occurs when magnetic field lines looping of the Sun's surface, many times larger than the Earth, get twisted and snap.
NASA's STEREO and Solar Dynamics Observatory observed a strong CME earlier this week.
Earth is protected by a doughnut shaped magnetic shield which channels the constraint stream of energy and small particles (solar wind) around the planet. The huge bubble of charged energy and particles released by a CME can travel down those magnetic field lines to the hole in that magnetic doughnut and into the atmosphere.
These particles interact with gasses in the upper atmosphere creating light displays in the north (Auroral Borealis) and south (Aurora Australis). Oxygen gives off green and red light. Nitrogen glows blue and purple.
The stronger the CME, the further south these displays are visible. Some are larger and travel faster, up to 2000 miles per second. On average they travel about 300 miles per second, crossing the nearly 93 million miles between the Sun and Earth in about 3.5 days. Not all those releases are in the direction of Earth either.
NOAA's Space Weather Prediction Center issued a Geomagnetic Storm watch for December 9-11 after NASA's STEREO and Solar Dynamics Observatory spotted the CME which is forecasted to bring geomagnetic levels to minor levels (G1) tonight, December 9, increasing to strong (G3) on Thursday.