Bz Archives

A strong G3 geomagetic storm surged across the planet this morning producing a spectacular display of the northern lights. Some of you may who may have risen to see the new nova were no doubt as surprised as the NOAA space weather folks, whose overnight forecast did not include an alert for even a minor storm.

So what happened? Let’s just say the Sun isn’t always as predictable as we’d like. An interplanetary shock wave in the form of a sudden increase in the solar wind speed from 250 miles per second to 375 mph (400-600 km/sec) began blasting Earth shortly before midnight. It appears the combined effects of earlier coronal mass ejections (CMEs) and an outpouring of high-speed solar particles from a gaping hole in the Sun’s magnetic canopy crashed through Earth’s magnetic defenses.

Particle-wise, all hell broke loose. You can start looking for more as soon as it gets dark tonight.

A powerful X2.2-class flare from sunspot region 2297 glows fiery yellow in this photo taken by NASA’s Solar Dynamics Observatory on March 11, 2015. Credit: NASA — A powerful X2.2-class flare from sunspot region 2297 glows intensely in this photo taken in short wavelength ultraviolet light by NASA’s Solar Dynamics Observatory on March 11, 2015. Credit: NASA Goddard SDO

We know that recent flares from sunspot group 2297 have sent more than a few billows of solar particles our way called CMEs or coronal mass ejections. Weekend forecasts called for minor storms but little materialized. Only when we thought it was safe to go back to bed did the aurora pounce. Reading the magnetospheric tea leaves, better known as the Kp index, a measure of magnetic activity high overhead in Earth’s ionosphere, quiet conditions gave way to auroral abandon starting around 1 a.m (CDT) today.

A wall of colorful red and green aurora met the eye and camera of Jim Schaff of Duluth this morning around 3 a.m. CDT. Credit: Jim Schaff

Like a spring grassfire the northern lights took off from there and burned till dawn, peaking between 2 and 4 a.m. Most of us are usually asleep during those deep hours of the night, but I’m hoping those who arose to see the nova or catch the lunar crescent at dawn may have been as surprised and delighted as I was to see auroras.

Like paw prints made by a cat, pale green auroral rays mark the northern sky around 5:45 a.m this morning March 17. Credit: Bob King

More are in the offing. The latest space weather forecast calls for continued severe storms (G3 or higher) to continue through tonight. G1 or minor storms are normally only visible as arcs or low rays across the north from the northern tier of states, but if tonight’s forecast holds, a fair portion of the U.S. should see auroras. Keep an eye peeled for bright, moving glow and arcs across the northern sky.

The awesome 30-minute aurora forecast map updates the shrinking and expanding of Earth's northern auroral oval due to changes in the solar wind from CMEs, flares and the like. This view is from this morning around 4:55 a.m. Red indicates intense aurora. Credit: NOAA — The awesome 30-minute aurora forecast map updates the shrinking and expanding of Earth’s northern auroral oval due to changes in the solar wind from CMEs, flares and the like. This view is from this morning around 4:55 a.m. Red indicates intense aurora. Credit: NOAA

There are lots of tools available you can use yourself to know if auroras are lurking about. First, check the NOAA 3-day space weather forecast. There you’ll see a list of times along with a Kp index number indicating magnetic activity. Number “1-4” means no storm and little likelihood you’ll see an aurora. “5” indicates a minor storm; the higher the number the more severe the storm and more widespread the northern lights will be.

Curtains of aurora still pushed through the growing light of dawn. Credit: Bob King — Curtains of aurora still pushed through the growing light of dawn (blue sky at top). Credit: Bob King

There’s also a nice visual representation of the numbers on the Planetary K-index site, where magnetic activity is updated every 3 hours. The dashed line on the bar chart represents 0 UT or 7 p.m. CDT. One of my favorites and the ultimate visual feast of an aurora indicator is NOAA’s Aurora 30-minute Forecast. Here you get a birds-eye representation of the current aurora based on satellite data. When the permanent auroral oval expands southward and intensifies, put on your coat and head out for a look. For education and entertainment, click on the gray arrow below the graphic and you’ll see a whole day’s worth of activity play out before your eyes. Totes cool.

ACE plot from a June 2013 aurora. Note the steep drop in the Bz. Credit: NOAA — ACE plot from a June 2013 aurora. Note the steep drop in the Bz. ACE orbits around the L1 Lagrange point about a million miles ahead of Earth in the direction of the Sun. There it studies the incoming particle streams from the Sun hours before they reach Earth. Credit: NOAA

I’m also in big believer in the the Advanced Composition Explorer (ACE) Bz plot. Bz is the direction of the embedded solar magnetic field that gift-wraps the streams of high-speed particles sent our way by the Sun. Like a magnet, it has a south pole and a north pole. When the south pole of the field sweeps by – what scientists call a negative Bz – the blast is more likely to link up with Earth’s magnetic field and spark auroras. When you see the Bz “head south” to -5 or lower, there’s a chance for auroras.

Now that you’re armed with information, cross your fingers all the indicators will point in the right direction for the aurora to continue tonight. And yes, Happy St. Patrick’s Day!

Skiing stop to take in the northern lights near Fairbanks Monday night. Credit: John Chumack — Skywatchers stop to take in the northern lights near Fairbanks Monday night. Credit: John Chumack

UPDATE: The storm continues and is now rated G4 or severe as of 10 a.m. CDT. Lucky for you if you live somewhere where it’s dark right now.

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

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.

Tag: Bz

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