Hopkins Student Forecasts Cosmic Storms
Even a half-hour's warning could provide enough time for technicians to take precautions to avoid damage to satellites and to electrical transformers on Earth, said Ashok Kumar, who has devised the method as part of his doctoral research in astrophysics.
"It's almost like weather forecasting," said David Rust, a solar physicist at Johns Hopkins' Applied Physics Laboratory and co-author of a scientific paper on the research.
Kumar presented the paper May 31 during the American Geophysical Union's spring meeting, at the Baltimore Convention Center. It is entitled "Evolution and Solar Origins of Interplanetary Magnetic Clouds: Role of Magnetic Helicity Conservation."
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 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 magnetic clouds comes close enough to Earth to disturb the planet's magnetic field. The eruptions generate highly energetic subatomic particles that would be potentially lethal to astronauts working in deep space or on the moon. The Earth's own magnetic fields normally protect the space shuttle astronauts.
When the magnetic clouds 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," Rust said.
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 very successfully to calculate details such as the temperature and the pressure of magnetic fields in laboratory fusion power experiments.
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.
"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," Rust said.
When Kumar tested his equations on previous observations of magnetic clouds, the predictions matched the actual behavior of the clouds. Rust will give a related talk at the AGU meeting, at 9:30 a.m. on Tuesday, May 30. The title of his paper is "The Origin of Solar Eruptions: Helical m=1 Kink Instability in Chromospheric Filaments."
Kumar also will present his work during a meeting of the American Astronomical Society's Solar Physics Division, June 4-8 in Memphis, Tenn., and during a conference on solar winds, June 25- 30 in Dana Point, Calif.
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