Southern and northern lights sweep planet in stunning display of auroras — The Washington Post #aurora

Click the link to read the article on The Washington Post website (Matthew Cappucci and Kasha Patel). Click through for the video, photos, and Twitter stream. Here’s an excerpt:

A ‘severe’ solar storm triggered the outburst of auroras. Even California, Arizona, Arkansas and Virginia reported sightings.

Skywatchers in Europe, Asia and North America were treated Sunday night to perhaps one of the most widespread displays of the northern lights since the autumn solar storms of 2003. Equally impressive shows of the aurora australis, or southern lights, were spotted in Australia and New Zealand.

The northern and southern lights, collectively known as the aurora, are most common in the high Arctic and Antarctic regions around the poles, but they can venture to the middle latitudes on rare occasions during potent geomagnetic storms. The storms are caused by magnetic energy and electrons that are hurled into space by the sun. The stronger the solar storm, the greater the effect — particularly if the resulting outburst is directed toward Earth. Forecasters at the Space Weather Prediction Center in Boulder, Colo., issued warnings for a Level 4 out of 5 “severe” geomagnetic storm, which happens on average only 60 times every 11 years. The episode may have been even more intense at times, sparking auroral displays as far south as California, Arizona, Arkansas and Virginia…

On Friday afternoon, NASA’s Solar Dynamics Observatory satellite recorded an explosion on the surface of the sun. The flare, rated an M2 on an ascending scale that climbs A, B, C, M to X, caused a radio burst on Earth eight minutes later. That clued NOAA forecasters into the fact that the energy was directed toward Earth…The flare was followed by a coronal mass ejection (CME) — a mass of solar plasma, charged particles and magnetism — that headed directly toward Earth at speeds of roughly 1.5 million miles per hour. That interplanetary shock wave collided with Earth’s magnetic field on Sunday afternoon Eastern time, which was after dark in Europe and in the early hours of Monday in China. Brilliant apparitions of the northern lights quickly appeared. The CME brought “severe” geomagnetic storming, stronger than what the Space Weather Prediction Center forecast when the CME left the sun Friday…

The colors of an aurora correspond to the type and altitude of the element that is excited in Earth’s atmosphere, Murtagh explained. Excited oxygen atoms glow red above 120 miles and glow green between 60 and 120 miles. Excited nitrogen atoms below 120 miles can glow pink or purple. Murtagh said a more intense aurora is typically higher, so lower latitudes will see more red.

“The bigger storms can light up the higher altitudes, which is largely going to [excite] the oxygen causing that red,” he said. “The further you are away, down south that is, you’re going to not see the green and yellow in the lower altitudes.”

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