Auroras Offer Clues to Mysteries of Solar Activity

It's nearly midnight as Tom Hallinan steers his tiny sedan up a winding road flanked by walls of Arctic evergreens flocked with snow.

Earlier in the evening, the University of Alaska geophysicist phoned to say his wife had looked out a window of their home and had seen the northern lights. "Would you like to head up to Poker Flat tonight and view the aurora?" he asks.

At 11:45, he pulls into a darkened parking area outside of one of the world's premier aurora observatories, run by the University of Alaska at Fairbanks' Geophysical Institute, which is built on a hillside at the institute's Poker Flat Research Range.

Tonight's display is breathtaking, as curtains, arcs, and swirls of pale light move across the sky. But it's merely a preview of coming attractions. The sun, which drives the aurora, is beginning to build toward the peak of its 11-year sunspot cycle. Researchers estimate that solar activity will reach its zenith between March 1999 and June 2001.

Auroral displays will grow more dramatic and may play to a wider audience as storms on the sun's surface grow more intense. The warm-ups already are under way. Last April, an auroral display was visible from parts of central Massachusetts, while reports of the northern lights' dance came in from Maine, New Hampshire, and northern Michigan over last Columbus Day weekend.

A tour of the observatory shows the two-story building serves as the control center for the sounding rockets launched at the range, as well as a collection point for data from cameras and other sensors at the range and at similar observatories around the globe. These constantly monitor the night sky for clues that will help scientists unravel the auroras' secrets.

After the tour, Dr. Hallinan settles down in the facility's kitchen, unloads a small grocery bag - standard issue for his frequent nighttime trips from Fairbanks some 30 miles away - and offers the fixings of a peanut butter and jelly sandwich. Between bites, he explains the mighty dynamo that drives aurora and sketches some of the elementary questions about auroral displays that scientists struggle to answer. The information they tease from these enigmatic light shows not only will help deepen their understanding of auroras, it also could help improve forecasts of space weather, of which auroras are the most visible evidence.

Bright lights, big collisions

The story, Hallinan says, starts with the sun, which continuously sheds charged particles as solar wind. Some of these particles penetrate the Earth's magnetosphere, get trapped, and then drawn down the Earth's magnetic field lines toward the North and South magnetic poles. At 250 to 300 kilometers (155 to 186 miles) above the Earth, the show begins as incoming particles slam into various gases in the atmosphere, turning the sky into nature's equivalent of a neon light. Incoming protons capture electrons to form hydrogen, giving off blue light in the process. Electrons collide with nitrogen, emitting a blue or red glow, depending on the nitrogen's form. Electrons also collide with oxygen, which emits green and red light, depending on the oxygen's form.

These latter collisions dominated the Great Red Aurora of March 13, 1989. "People saw that as far south as the Yucatan Peninsula and Florida, and thought it was from a forest fire," Hallinan says. "It caused a regionwide power outage in Quebec."

By the time the particles have dropped to about 100 kilometers above the Earth's surface, they've either been captured or are moving too slowly to elicit a glow from the gasses they hit.

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