Understanding the
sun's fury
By Diane
Ainsworth, Public Affairs
Posted July 12, 2000
A torrent of far-ultraviolet data from a massive explosion of hot gases that had lifted off the sun two days before awaited Harald Frey, a research physicist on the morning of June 8. The brunt of a ghostly light show illuminating the northern skies, known as the aurora borealis, had arrived.
Frey was prepared for the onslaught of information he would retrieve from an instrument onboard NASA's new Imager for Magnetopause-to-Aurora Global Exploration, or IMAGE, spacecraft -- the first weather satellite for space storms -- but ecstatic at the level of detail he saw in the images on his computer screen.
"We were able to see very minute details in the structure and shape of this electrified halo over earth's northern pole," he said, thumbing through page after page of the latest pictures in the IMAGE mission data-processing center on the third floor of Berkeley's Space Sciences Laboratory. "The far-ultraviolet imager takes a snapshot every two minutes of the auroral ovals over the North Pole and depicts the aurora, the zone of fire created by the collision of protons and electrons with earth's upper atmosphere. We were able to image the evolution of the northern lights over four hours, as the spacecraft was moving away from the northern pole, and turn that sequence of images into a quick-time movie for the world to see."
The titanic blob of charged particles -- a "coronal mass ejection" or CME -- that had burst free from the sun and was pummeling earth's protective magnetic bubble, known as the magnetosphere, had damaged two commercial satellites on June 6. By late that afternoon, severe magnetic disturbances in the upper atmosphere had knocked out power at Foxboro Stadium in Massachusetts and left 16,000 fans sitting in the rain, just minutes after the United States had tied the Irish in a World Cup match.
Despite a precautionary alert of intensifying geomagnetic turbulence issued that day by the National Oceanic and Atmospheric Administration, officials were not able to predict the peak of the storm's fury. Perplexed, power and telecommunications companies watched and waited, hoping the solar storm would blow over. On June 8, a blast of x-ray and ultraviolet radiation seared earth's upper atmosphere and triggered a blackout affecting 24,000 residents in a suburb of Chicago.
Much of the magnetic interference that stirs the earth's upper atmosphere is spawned by coronal mass ejections on the sun. These eruptions, which are expected to increase as the sun nears the peak of its 11-year solar cycle later this year, tear huge holes in the sun's outer atmosphere, or corona, and shoot billions of tons of highly energetic particles at planets, much like a garden hose, at speeds of more than 1 million miles per hour. When these blasts of high energy particles strike the earth's tear-shaped magnetosphere and activate its gigantic power generator, the collision sends enormous currents into the earth's atmosphere, producing a brilliant ring of greenish-reddish aurora in the night sky.
"A significant gap in our understanding of auroras has come from our inability to image proton auroras, which make up a large part of the aurora, because they are very diffuse and are almost invisible to the naked eye," said Stephen Mende, an atmospheric physicist and lead investigator of the far-ultraviolet instrument team housed in the university's space sciences laboratories atop Grizzly Peak. "Now we will be able to make them distinctly visible and track them in far-ultraviolet wavelengths."
A variety of imaging techniques will be used during IMAGE's two-year primary mission to give scientists the first comprehensive pictures of the full extent of earth's magnetosphere. Most charged particles are invisible on their own, but helium charged particles glow in the ultraviolet when illuminated by sunlight, and most types make the atmosphere luminous when colliding with it, causing ultraviolet light. Or they will neutralize themselves and form neutral particle beams, which can also be observed by IMAGE's many cameras. In addition to the two-dimensional imagers, the spacecraft carries a radio sounder to obtain global images of the primary plasma regions and boundaries of earth's inner magnetosphere. This radio sounder is a specialized "radar" that will detect charged particle clouds.
"Our first ultraviolet images are a good example of that new capability to see fine structure in an aurora that was invisible before," said Frey, who is charged with processing and analyzing all of the data before posting it on the Internet (http://ssl.berkeley.edu/research.shtml). "The pictures show an oval-shaped aurora extending more than 4000 kilometers (2000 miles) across in a complete ring, with a richness of structure that we did not expect to see, as the geomagnetic storm progressed.
"The oval could be easily traced into the daylight portion of the earth, where it narrowed considerably into a thin ribbon only a few hundred miles thick," he added. "On the night side, we saw a dramatic broadening of the oval as the aurora evolved over time."
The evolution of the aurora from the onset of the storm -- that huge blob of coronal material unleashed on June 6 -- was recorded by the IMAGE instruments. Data are being received via a 36-foot satellite dish outside Frey's data-processing lab. The antenna will be used next year for the High Energy Solar Spectroscopic Imager mission, which will allow scientists to fully monitor the progress of these distant events and study their impact on the movements of other plasma systems closer to earth during solar maximum.
"The far-ultraviolet imager system is one of five suites of camera systems onboard IMAGE. The instrument observes the aurora in three wavelengths: at very short wavelengths of 120 to 124 nanometers, where mainly hydrogen emissions can be seen; at 135.6 nanometers, where oxygen atoms are visible; and at 140 to 180 nanometers, where nitrogen emissions are best seen. (A nanometer is one-billionth of a meter.) By comparison, the human eye can only see visible wavelengths that are slightly longer than 400 nanometers but do not exceed 660 nanometers.
Over the next two years, the far-ultraviolet imager and its coterie of complementary cameras will gather data while the spacecraft orbits the poles, passing within 620 miles of the southern hemisphere at its closest approach to earth and 27,680 miles from the northern hemisphere at the farthest point in its orbit.
Data from the half-ton satellite will be used in parallel with data from several Earth-orbiting probes currently in flight, such as NASA's Polar spacecraft and Japan's Geotail spacecraft, to describe how the magnetosphere changes in shape or configuration and how it processes the charged particles it has acquired from the sun, Mende said.
"We don't fully understand all the ways in which the sun is affecting us by providing light, heat, bursts of energetic particles and other solar activity, but it is increasingly important that we find out about this sun-earth connection," added Janet Luhmann, a space physicist on another new solar probe called STEREO. "Those complex interactions affect everything we do, our telecommunications and some of the latest technologies in other industries. They may influence our weather patterns and they will determine our future in space, what astronauts are able to withstand and accomplish in the years ahead."
July 12 - August 16,
2000 (Volume 29, Number 1)
Copyright 2000, The Regents of the University of
California.
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