Forecast Calls For Magnetic Storms Emil Venere --------------------------------- Homewood News and Information It may not be long before the daily weather forecast calls for cloudy skies and periods of rain, with a strong possibility of magnetic storms. Hopkins doctoral student Ashok Kumar has devised a method for improving forecasts of powerful magnetic storms caused by the sun--information that could help prevent millions of dollars of damage to orbiting spacecraft and to electric power lines on Earth. Forecasting magnetic storms might also one day help prevent serious injury or even death. The radiation from such space storms would be potentially lethal to astronauts venturing outside the veil of Earth's magnetosphere, which protects present-day astronauts on the space shuttle, for example. But in the not-too-distant future, people will be traveling and working in deeper space or on the moon. Even a half-hour's warning could be enough time for technicians to switch off sensitive equipment, and for spacefarers to take cover in shielded areas. "If they had some warning they could take precautions," said the 29-year-old Kumar, who got the idea for his forecasting model while working with Professor David Rust, a solar physicist at the Applied Physics Laboratory. Kumar developed the model as part of his doctoral research in astrophysics and presented a scientific paper on the work during several conferences in June. The paper was co-written by Rust. "It's almost like weather forecasting," Rust said. "It has a nice predictive possibility because you see something go off on the sun, and you can say, four days from now it's going to hit the Earth and it's going to have such and such magnetic field, and carry so much force." The dangerous storms originate in the sun's atmosphere, where "filaments" of twisted magnetic fields are periodically generated. The filaments trap a large amount of material, forming "clouds" that are suspended in the solar atmosphere by magnetic fields. Due to a mechanism that remains a mystery, the filaments twist into a helix shape, developing kinks that cause them to spring out of the sun's atmosphere and into space. These solar eruptions of mostly hydrogen gas generate highly energetic subatomic particles and speed away from the sun at about 500 kilometers per second (more than a million miles per hour). At that speed they can reach Earth within four days. About three times a month, one of these huge magnetic clouds comes close enough to Earth to disturb the planet's magnetic field. "They tend to be close to 4,000 times the size of Earth," Kumar said. When they hit the Earth they interact with the planet's magnetosphere, inducing magnetic storms that can damage satellites and heat the upper atmosphere. The heating causes the atmosphere to expand slightly and pulls satellites into lower orbits. Eventually, the atmosphere will drag such satellites down to an early death. Disturbing the Earth's magnetic field also results in an acceleration of subatomic particles that can cause major damage to a satellite's electronic components. On Earth's surface, the storms can produce currents in high-voltage power lines, prompting transformers to overload and explode. "These storms have very definite and expensive consequences," said Rust, head of APL's Center for Applied Solar Physics. An important factor in Kumar's forecasting system is that the filaments have characteristic twists, just like the spiral of threads on a machine screw. For example, most screws twist to the right so that rotating them clockwise causes them to go forward. Scientists use the term "helicity" to describe this twisting motion with a direction. If the filaments originate in the sun's northern hemisphere, they have left-handed twists, and if they are in the southern hemisphere, they have right-handed twists. Kumar has been able to take advantage of the fact that a magnetic filament leaving the sun's atmosphere can be identified by the characteristics of its twisting field. His model then predicts how the filament will expand and heat up on its trip through space. "When one of these right-handed filaments erupts from the sun, and if it comes past the Earth, you detect a right-handed magnetic field in it," Rust said. Scientists believe that a specific filament's helicity does not change once it has been formed. This "conservation of helicity" principle has never been used before to make predictions about events on a cosmic scale. But it has been used to calculate details such as the temperature and the pressure of magnetic fields in laboratory nuclear fusion experiments, Rust said. It is an essential component of Kumar's forecasting equations. Astronomers observing the sun's atmosphere can tell a cloud's original characteristics, such as its temperature, size and mass. But, while those characteristics change with time, the helicity is a constant. As a constant, it can be applied in mathematical formulas to predict a magnetic cloud's shape and strength by the time it reaches Earth. The model cannot be used for real-life weather forecasting, however, until satellites are placed in space to better monitor sun activity, Rust said.
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