Johns Hopkins Gazette: July 24, 1995

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

     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

     "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

     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

     "These storms have very definite and expensive
consequences," said Rust, head of APL's Center for Applied Solar

     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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