June 5, 2000 Three-dimensional images of magnetic storms from the Sun, developed by physicists at the University of California, San Diego and Japan’s Nagoya University, are allowing space-weather forecasters to improve their predictions of solar disruptions on cycle.
These large magnetic storms are produced by energetic solar eruptions known as "coronal mass ejections" that consist of giant clouds of energetic electrons and strong magnetic fields traveling from the Sun at up to 2 million miles an hour. When they reach Earth, the coronal mass ejections and the storms they cause can interrupt satellite communications, produce destructive surges in power grids and even increase radiation exposure to people flying in airplanes.
Space-weather forecasters have for years issued warnings of these storms whenever they detected a coronal mass ejection, or solar flare, near the Sun. But because they could not see the mass ejection traveling through space, they could not tell with any certainty whether it would affect Earth when it arrived four days later or whether it would totally bypass the planet.
Using a network of four radio telescopes in Japan, UCSD and Nagoya University physicists have improved those predictions dramatically by developing a method of detecting and predicting the movements of these geomagnetic storms in the vast region of space between the Sun and Earth. By focusing the telescopes on powerful sources of natural radio emissions in the universe, the physicists infer the location of these storms by the intensity fluctuations, or "scintillation," they produce in the radio sources.
"Basically, the more scintillation there is, the more material there is along the line of sight," says Bernard V. Jackson, a solar physicist at UCSD’s Center for Astrophysics and Space Sciences who developed the detection technique with Masayoshi Kojima of Nagoya University’s Solar-Terrestrial Environment Laboratory. "It’s the same reason stars twinkle. In the case of the twinkling stars, the fluctuations are caused by changes in the atmosphere, which cause scintillation of the starlight."
The scientists are able to detect the direction and velocity of the storms by precisely measuring when a particular fluctuation, or "twinkle," reaches each of the four radio telescopes, which are separated from one another in four Japanese radio sites. "If you have four radio telescopes not too far apart, then you can correlate the time the scintillation pattern goes from one telescope to the other," says Jackson. "That allows you to say how fast the material is moving." Combining all of the information in a computer program, the scientists produce a three-dimensional picture of the region between the Sun and Earth—a view Jackson says is similar to "a CAT-scan of the solar wind."
That information is then sent to the National Oceanic and Atmospheric Administration’s Space Environment Center in Boulder, Colo., which provides forecasts and warnings of space-weather disturbances. The center is now closely watching for coronal mass ejections, which become more frequent as the Sun approaches the peak of its 11-year cycle. Because the scientists’ technique, known as three-dimensional tomography, was not available the last time the Sun reached its peak period of activity, forecasters at the center will be able to make much more accurate predictions of any geomagnetic storms that affect Earth than they did during the last solar maximum.
Jackson estimates that the accuracy of the forecasts will be improved dramatically once again when a U.S. Air Force satellite is launched in December, 2001, carrying an instrument that will take direct pictures of the mass ejections between the Sun and Earth by detecting the sunlight that is reflected from the clouds of electrons in a process known as Thomson scattering. Called the Solar Mass Ejection Imager, the instrument, which is being built with Air Force and National Aeronautics and Space Administration financing, eliminates stray sunlight and precisely removes the effects of starlight from one image to the next to detect the faint Thomson scattering of sunlight from the electrons. It was designed by a team of scientists that includes Jackson, UCSD physicists Andrew Buffington and P. Paul Hick, and colleagues at the Air Force Research Laboratory, University of Birmingham in the U.K., Boston College, Boston University, the Johns Hopkins University’s Applied Physics Laboratory and the Naval Research Laboratory.
"We’ll get a thousand times more data from the Solar Mass Ejection Imager and we’ll be able to resolve these things by an order of magnitude better," says Jackson. "We know coronal mass ejections are important and we know they cause effects on Earth. But until now we didn’t have a way to view them very well."
"We are now at the stage where weather forecasting on global scales was 30 years ago, when satellites first became available," he adds. "We discovered then that we could see hurricanes really well from a satellite and could tell what direction they were going in and could watch them over time to predict where they were going to make landfall. We’re now at the same point with coronal mass ejections."
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