Posted on by Bob King

Spectacular Aurora Sneaks in Quietly, Rages All Night

Auroral arcs are topped by red rays light up the northeast while the moon and Jupiter shine off to the west in this photo taken last night over a small lake north of Duluth, Minn. Both moon and aurora light are reflected in puddles on the ice. Credit: Bob King

Expect the unexpected when it comes to northern lights. Last night beautifully illustrated nature’s penchant for surprise. A change in the “magnetic direction” of the wind of particles from the sun called the solar wind made all the difference. Minor chances for auroras blossomed into a spectacular, night-long storm for observers at mid-northern latitudes.

 

6-hours of data from NASA's Advanced Composition Explorer spacecraft, which measures energetic particles from the sun and other sources from a spot 1.5 million kilometers ahead of Earth toward the sun. By watching the Bz graph, you'll get advance notice of the potential for auroras. Click to visit the site. Credit: NOAA
6-hours of data from NASA’s Advanced Composition Explorer spacecraft, which measures energetic particles from the sun and other sources from a spot 1.5 million kilometers ahead of Earth toward the sun. By watching the Bz graph, you’ll get advance notice of the potential for auroras. Click to visit the site. Credit: NOAA

Packaged with the sun’s wind are portions of its magnetic field. As that material – called the interplanetary magnetic field (IMF) – sweeps past Earth, it normally glides by, deflected by our protective magnetic field, and we’re no worse for the wear. But when the solar magnetic field points south – called a southward Bz – it can cancel Earth’s northward-pointing field at the point of contact, opening a portal. Once linked, the IMF dumps high-speed particles into our atmosphere to light up the sky with northern lights. 

A large red patch briefly glowed above the bright green arc around 11:15 p.m. CDT last night May 3. The color was faintly visible with the naked eye. Credit: Bob King
A large red patch briefly glowed above the bright green arc around 11:15 p.m. CDT last night May 3. The color was faintly visible with the naked eye. Credit: Bob King

Spiraling down magnetic field lines like firefighters on firepoles, billions of tiny solar electrons strike oxygen and nitrogen molecules in the thin air 60-125 miles up. When the excited atoms return back to their normal rest states, they shoot off niblets of green and red light that together wash the sky in multicolor arcs and rays. Early yesterday evening, the Bz plot in the ACE satellite data dipped sharply southward (above), setting the stage for a potential auroral display.

After an intial flurry of bright rays, the aurora scaled back to two bright, diffuse arcs before erupting again around 11:30 p.m. Credit: Bob King
After an initial flurry of bright rays, the aurora scaled back to two bright, diffuse arcs with subtle rayed textures before erupting again around 11:30 p.m. Credit: Bob King

Nothing in the space weather forecast would have led you to believe northern lights were in the offing for mid-latitude skywatchers last night. Maybe a small possibility of a glow very low on the northern horizon. Instead we got the full-blown show. Nearly every form of aurora put in an appearance from multi-layered arcs spanning the northern sky to glowing red patches, crisp green rays and the bizarre flaming aurora. “Flames” look like waves or ripples of light rapidly fluttering from the bottom to the top of an auroral display. Absolutely unearthly in appearance and yet only 100 miles away.


VLF Auroral Chorus by Mark Dennison

I even broke out a hand-held VLF (very low frequency) radio and listened to the faint but crazy cosmic sounds of electrons diving through Earth’s magnetosphere. When my electron-jazzed brain finally hit the wall at 4 a.m., flames of moderately bright aurora still rippled across the north.

Just when you thought it was over, the whole northern sky burst into rays around 1 a.m. CDT. The whole northern sky lit up with green and red rays earlier this morning. While the green color was easy to see, the red was very pale. The human eye is much more sensitive to green light than red, one of the reasons why the aurora rarely appears red except in a camera during a time exposure. Credit: Bob King
Just when you thought it was over, the whole northern sky burst into rays around 1 a.m. CDT this morning. The human eye is much more sensitive to green light than red, one of the reasons why the aurora rarely appears red except in time exposures made with a camera. Credit: Bob King
Around 2 o'clock the northern lights displayed flaming when ripples of light pulse from top to bottom. It's very difficult to photograph, but here it is anyway! Credit: Bob King
Around 2 o’clock, flames pulsed from bottom to top in patchy aurora. It’s very difficult to photograph, but here it is anyway! Credit: Bob King

So what about tonight? Just like last night, there’s only a 5% chance of a minor storm. Take a look anyway –  nature always has a surprise or two up her sleeve.