Geomagnetic storm sparks vivid northern lights show
- Ellie Ruel
- 1 hour ago
- 3 min read
Chasing what makes a bright aurora: Why were more intense shades visible in Juneau?
By Ellie Ruel
Juneau Independent
The aurora borealis lit up skies across most of the northern half of the country for the last two nights after a G4 geomagnetic storm. In Juneau, swatches of red and green light with less common splashes of magenta were visible over the mountains even as clouds set in Wednesday night.
Wednesday’s CME was the highest energy and fastest, paired with one of the most intense solar flares of the current solar cycle. The National Oceanic and Atmospheric Administration and National Aeronautics and Space Administration announced the sun had reached its most active phase of its 11-year cycle in October of last year.
The storm was caused by three Earth-directed coronal mass ejections (CME), expulsions of solar material from the sun’s outermost atmosphere that cause disruptions in the magnetosphere if they reach Earth. These ejections usually start when the multitude of magnetic fields in the sun get twisted as the equator rotates faster than the poles. When contorted enough, the fields can snap and reconnect, releasing energy.
A geomagnetic storm occurs when the charged particles and energy of a CME hits the Earth’s magnetosphere that acts as a shield. The excess energy excites atoms in the atmosphere, releasing photons as electrons relax back into a stable state. Those photons can be emitted from different energy levels depending on the atom type, creating different wavelengths of light that cause the aurora borealis.
Hydrogen atoms, generally found lower in the atmosphere, produce pinkish-crimson hues when excited. Pink, blue and violet are emitted by nitrogen, which can also produce a turquoise bluish green. That green is usually silenced by the most commonly observed green produced by oxygen about 60 to 90 miles up in the atmosphere. At higher elevations where the particles are less dense, oxygen can also give off red light.
In Juneau, most of those shades made an appearance at one point or another. A crowd of aurora watchers gathered at the Mendenhall Glacier pavilion, holding their phones up to the sky as steadily as possible for long exposure shots that amplified the colors.
According to the Space Weather Prediction Center, the highest intensity storming has likely passed, with the possibility of G2-G3, corresponding to Kp values (a scale of one to nine that measures the disruptions of the magnetosphere from solar wind) of six to seven, lower energy impacts throughout Thursday. The University of Alaska Fairbanks Geophysical Institute is predicting Kp values of five to six for Thursday night.
• Contact Ellie Ruel at ellie.ruel@juneauindependent.com.
