Moving through space at a speed 10 times faster than sound, solar wind particles have been known to cause blackouts in major cities. Solar wind also endangers astronauts, and it can wreak havoc on cellular telephone users. But researchers won't be able to predict the antics of solar wind, and perhaps minimize its impacts, until they can better understand the phenomenon.
Some researchers think the sun generates smooth "waves" of solar wind particles, which flow rhythmically through space until a small number (only 10 to 30 per cubic centimeter) reach the earth's orbit. New data paints a less benign picture of solar wind, according to graduate student Robert J. Leamon and researchers William H. Matthaeus, Norman F. Ness and Charles W. Smith of the renowned Bartol Research Institute at UD.
"If you're walking in a very windy city, you're being buffeted by these powerful gusts, and it's blowing the hat right off your head," Smith explains. "We think the solar wind is similarly mischievous. It moves dynamically, like an atmospheric storm."
As solar wind dissipates, pulling the sun's magnetic field along with it, the gaseous protons and electrons that form the solar plasma gyrate in a circular orbit, Matthaeus says. These plasma fluctuations "couple" and spin off new fluctuations in a cascade that concludes when the plasma fluctuations heat the background ions. By the time it reaches a frequency of about one-half Hertz, Smith says, solar wind fluctuations dissipate.
In other words, Matthaeus says, "When the fluid-flow patterns of the plasma match up in size with the spiral patterns of magnetized particles, their coupling puts an end to these nice, fluid motions and excites random motions, which generate heat. Evidence of these events strongly suggests that the idea of solar wind as a simple, wave-like entity can't be accurate." By understanding exactly how solar wind fluctuates and dissipates as it flows from the sun to the Earth, he adds, it may someday be possible to predict cosmic disturbances.
When NASA launches its new Advanced Composition Explorer (ACE) spacecraft in August, UD researchers will play a key role in analyzing its data and then submitting information, in real-time, to the National Oceanic and Atmospheric Administration. "The data might be useful, say, to warn astronauts and others in high-altitude craft to fly at lower altitudes," Smith says. "Utility companies also could receive advance warning of solar wind disturbances, allowing them to prepare backup or off-peak systems."
Information presented today was collected during 34 one-hour atmospheric events. Parameters such as the temperature, density, velocity and energy of particles were generated by a magnetometer and other instruments aboard the National Aeronautics and Space Administration's WIND satellite, deployed as part of the International Solar Terrestrial Physics program. The research was sponsored by NASA.
AGU Presentation Information:
Baltimore Convention Center, Hall E (poster SH41B-01)
Thursday, May 29, 1997, 8:30 a.m. EDT