On Nov. 20, 2003, a modest solar explosion sparked auroras in some unusual places.
Dec. 5, 2003: Photographer Jim Reed couldn't believe his eyes. The sun had just set over South Carolina on Thursday, Nov. 20th, and the sky, instead of growing dark, turned green and red. It was the aurora borealisa.k.a. the Northern Lightsshining through the bright city lights of Myrtle Beach.
"I kept walking east for a better view until I was literally standing in the Atlantic Ocean," he recalls. "At one point I could see the auroras reflected in the sand of the beachextraordinary! Listening to the crashing waves while I photographed this magnificent display is something I'll never forget."
Right: Northern Lights over Myrtle Beach, South Carolina, on Nov. 20, 2003. Credit: Jim Reed Photography.
Further south in Huntsville, Alabama, NASA solar physicist David Hathaway was watching the evening news when the weatherman announced that auroras had just been seen in the area. "I didn't believe him," says Hathaway, who didn't bother going outside to look. "Northern Lights in Alabama are that rare."
The storm began when a coronal mass ejection (CME) swept past Earth. CMEs are billion-ton clouds of gas hurled into space by explosions on the sun. When they strike Earth's magnetic field, CMEs sometimes spark geomagnetic storms and auroras.
"The CME of Nov. 20th was fairly run-of-the-millwhich is curious considering what happened when it arrived," notes Hathaway.
The cloud was propelled into space by an M4-class explosion on Nov. 18th near sunspot 501, an active region that had caused some intense space weather back in October, too. In this case, however, the explosion was not intense. M-class means "medium-sized"about ten times weaker than the much more powerful X-class flares feared by satellite operators and utility companies. M-class events happen perhaps a dozen times each month; they're ordinary. Yet this one triggered an extraordinary geomagnetic storm. Why?
Hathaway explains: "Earth's magnetic field acts like a shield; it protects us from CMEs and other solar activity. But CMEs can punch a hole in the shield. CMEs have a magnetic field of their own, and if a CME's magnetic field is tilted opposite Earth's magnetic field, the two will cancel out. This makes a hole or 'crack' in our planet's shielding into which solar wind energy can pour."
That's exactly what happened on Nov. 20th. In the wake of the CME came a south-pointing magnetic field measuring -50 nanoTeslafive to ten times bigger than usual. Our planet's magnetic defenses were breached, and the resulting geomagnetic storm was a whopper.
Left: Auroras over Huntsville, Alabama, on Nov. 20, 2003. Credit: NASA scientist Joe Minow.
NASA's IMAGE spacecraft and the European Space Agency's 4-satellite Cluster mission have recently observed geomagnetic cracks formed by CMEs. Some are as large as California and they can persist for many hours. Solar wind energy pours in, Earth's magnetic field shakes, and auroras appear where they are seldom seen.
"Of course," notes Hathaway, "the Northern Lights don't often get as far south as Alabama but sometimes they do." And--good news for sky watchers--it doesn't take a super-powerful solar flare to make it happen.
"Next time," he says, "I'm going outside."
Visit our Nov. 20th aurora gallery and browse hundreds of pictures from around the world.
The Sun Goes Haywire -- (Science@NASA) Solar maximum is years past, yet the sun has been remarkably active lately. Is the sunspot cycle broken?
Cracks in Earth's Magnetic Shield -- (Science@NASA) California-sized cracks in our planet's magnetic field can remain open for hours, allowing the solar wind to gush through and power stormy space weather.
Solar Superstorm -- (Science@NASA) Scientists are beginning to understand a historic solar storm in 1859.
SpaceWeather.com -- (Science@NASA) current information about solar activity and auroras
NOAA Space Environment Center -- the US government's official source of space weather data and forecasts
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