From National Wildlife Magazine...
|The aurora borealis, viewed near Fairbanks, Alaska; and the auroral "ring of fire" over North America, as seen from space. (Photos courtesy Malcolm Lockwood, Geophysical Institute, University of Alaska, and L.A. Frank, University of Iowa/NASA.)|
IT ALWAYS seems to happen when you expect it least. I remember driving home through Washington State late one December night when the sky to the north was suddenly cleaved by an arc of light. Shooting star effects played all along the line, and long pillars of light sporadically pulsed up beyond the zenith of the sky. White tinged with deep blues and greens predominated. Just after I crossed the Nooksack River, a lush red aurora burst out in the lower reaches of the arc. Deepening to a portentous magenta, the stain spread downward into the bare birch branches. Then as quickly as it had come, the aurora borealis -- the northern lights -- faded back to a pale distant greenish smear in the sky.
Despite the fact that this dramatic display was within view of millions of people in the Vancouver and Seattle areas, the show went almost entirely unnoticed. There were no forecasts or follow-ups in the media. One thousand miles away in Boulder, Colorado, however, researchers at the U.S. Space Environment Service Center had known there would be a strong aurora display almost a day in advance. Monitoring the sun with telescopes and satellites, they picked up what Phil Powell, a forecaster at the National Oceanic and Atmospheric Administration (NOAA), called "a major disturbance" on the surface of the sun which sent a stream of charged particles shooting through the solar system.
Scientists today believe that the aurora borealis is caused by these "solar wind" particles interacting with the Earth's geomagnetic field beyond the upper atmosphere in the area called the magnetosphere. According to Syun-Ichi Akasofu of the University of Alaska's Geophysical Institute, the solar wind generates huge quantities of electricity in the magnetosphere. This energy accelerates particles into the upper atmosphere where they strike atoms of various gases, producing the characteristic colors and staining the sky with dancing light.
The first person to make the a vital connection between the aurora and the sun was the English astronomer and physicist Richard Carrington. On September 1, 1859, he observed a solar flare. Two nights later, intense auroras covered much of Europe. Carrington immediately noted the connection but refused to jump to conclusions. ("One swallow does not make a summer," he remarked.) Despite his caution, Carrington's initial intuition was to have a tremendous effect on both astronomy and the heavenly notions of wider society, for it established once and for all that it was not ice, nor radium, nor torchlight on angels' wings, but mighty explosions on the sun that lit the northern lights.
The height of the aurora is roughly 65 miles above sea level, or ten times higher than the highest cloud. Typically, the aurora tends to follow a progression of forms during the course of the night. In the early evening, between 7 and 10 P.M., the aurora might appear as a smooth arc of light curving from horizon to horizon like a pearly rainbow. Later, the lights often become more active, dancing and developing vertical bars known as rays. The most expressive stage occurs around midnight or after, when the lights may show red and yellow in a variety of forms. During early morning, the aurora characteristically becomes patchy and paler, and may resemble the light in the sky above a nearby city or town.
Viewed from space, the aurora borealis and its southern twin, the aurora australis, appear as halos of fire around each pole. They may expand in diameter and distance from the poles (the stronger the current in the generator, the farther toward the equator the lights appear). However, recent photographic evidence has shown that they are almost always present. Rocket experiments conducted by the University of Minnesota have also shown that the aurora borealis and aurora australis mirror each other exactly. The most interesting of the many recent discoveries regarding the aurora, though, may be the existence of what researchers call the "theta aurora." On November 8, 1981, a University of Iowa experiment captured for the first time a sequence of images showing the formation and eventual breakup several hours later of an auroral bridge over the pole, resembling the cross piece in the Greek letter theta.
In ancient times, the northern lights were commonly seen as omens and indications of the supernatural, especially during those rare occasions when they appeared in more southerly latitudes. The Old Testament Book of Maccabees contains a wild description of gold-clad horsemen charging across the skies of the Middle East, which probably refers to a strong aurora around 176 B.C. The faerie horsemen of old Irish legends may also relate to of aurora, as may the descriptions of "fires in the air" over the Ardennes region of France in 1583. The latter sent thousands of penitents to Reims and Paris "to say their prayers and make offerings at the great churches," according to the journal of Henri III. Eskimos, who knew the aurora better than other cultures, were no less impressed. In Labrador, for instance, the natives long believed that the aurora marked the passage to heaven of the spirits of people who had died a voluntary or violent death.
The reign of science has diminished the awe that the aurora formerly inspired, but today people are actually more vulnerable to the power of the aurora and its geomagnetic disturbances than ever before. For one thing, it affects defense systems. Juan Roederer, director of the Geophysical Institute in Fairbanks, has written that strong auroras can interfere with early-warning radar watching for transpolar bomber attacks. During World War II, people noticed for the first time that the aurora could produce false images and other distortions on conventional radar, according to Neal B. Brown, range supervisor of the Geophysical Institute's Poker Flat research range. More advanced radar systems have also been shown to become ineffective when an aurora dimples the surface of reflective layers in the upper atmosphere. But North American Aerospace Defense Command (NORAD) spokesman Del Kindschi says that auroral storms would not prevent the United States earlywarning radar from picking up an over-the-pole attack.
It has only been with the development of large-scale electrical systems that the aurora -- which is essentially an electrical phenomenon -- has been able to touch the lives of humans directly. A significant amount of electrical energy flows to the surface of the Earth below the lights, and it is particularly drawn to large electrical grounds, such as power transmission lines and oil pipelines. When strong enough, this aurora can play havoc with man-made electrical systems by altering or overloading their power. In 1882, Scientific American reported that on November 17 "telegraphic communication was more or less interrupted over the northern half of the United States, and much damage was done to switchboards and other telegraphic devices. The disturbance extended across the sea ... and made itself felt in many parts of the European continent. Brilliant aurora were generally seen when the sky was clear."
Similar problems have been noted during other strong aurora, especially during "super storms"-prolonged surges of intense power that can sometimes approach the equator. In February 1958, for instance, a large part of northeastern Canada was blacked out when a super storm overloaded utility circuits. Human dependence on electrical devices has continued to increase dramatically, but interestingly, there have been no auroral super storms since.
"Statistically, we are overdue for a super storm," says Dave Speich of the Space Environment Service Center. "There are 20 auroral super storms on record since 1880 and none since 1960. We didn't have one during the last 11year cycle of sunspots, or this time either-at least so far." Tonight may be the night for the long overdue super storm, but more likely it will come when you least expect it.
"Shedding Light on the Aurora" originally appeared in the March 1985 issue of National Wildlife.