More Accurate Space Storm Warnings Now Possible

Dolores Beasley

Headquarters, Washington, DC

(Phone: 202/358-1753)

Susan Hendrix

Goddard Space Flight Center, Greenbelt, MD

(Phone: 301/286-7745)

RELEASE: 00-95

The arrival from the Sun of billion-ton electrified-gas
clouds that cause severe space storms can now be predicted to
within a half-day, a great improvement over the best previous
estimates of two to five days.

Scientists at the Catholic University of America, Washington,
DC, and NASA’s Goddard Space Flight Center, Greenbelt, MD, have
created a model that reliably predicts how much time it takes for
these clouds, called Coronal Mass Ejections (CMEs), to traverse
the gulf between the Sun and the Earth, based on their initial
speed from the Sun and their interaction with the solar wind.

The new model uses recent observations from the European
Space Agency/NASA Solar and Heliospheric Observatory (SOHO) and
the NASA WIND spacecraft. The model has been validated and made
more accurate using historical observations from the Helios-1
(Germany/NASA), the Pioneer Venus Orbiter (NASA), and the Space
Test Program P78-1 (United States Air Force) spacecraft.

Earth-directed CMEs cause space storms by interacting with
the Earth’s magnetic field, distorting its shape and accelerating
electrically charged particles (electrons and atomic nuclei)
trapped within. Severe solar weather is often heralded by dramatic
auroral displays (northern and southern lights), but space storms
are occasionally harmful, potentially disrupting satellites, radio
communications and power systems.

“The new model more accurately predicts the arrival of
Coronal Mass Ejections, and will greatly benefit people who
operate systems affected by space storms,” said lead author Dr.
Natchimuthuk Gopalswamy of Catholic University, a Senior Research
Associate at the National Academy of Sciences/National Research
Council. “The improved forecasts let operators of sensitive
systems take protective action at the proper time and minimize the
unproductive time when systems are placed in a safe mode to
weather the storm.”

Gopalswamy and colleagues will present this research today
during a meeting of the Solar Physics Division of the American
Astronomical Society at Lake Tahoe, Stateline, NV.

Coronal Mass Ejections leave the Sun at various speeds,
ranging from 12 to 1,250 miles (about 20 to 2,000 kilometers) per
second. Only the CMEs directed at Earth are potentially harmful;
estimating when they will arrive is difficult because their speed
changes due to interaction with the solar wind, a stream of
electrically charged gas blowing constantly from the Sun at about
250 miles (about 400 kilometers) per second.

Just as a motorboat heading downstream will slow to the speed
of the river’s current if its motor is turned off, Coronal Mass
Ejections starting out from the Sun more quickly than the solar
wind eventually are slowed by the drag of this “stream.” If a boat
pulls up anchor, it will gradually accelerate until it is moving
at the speed of the current. Similarly, CMEs that start out more
slowly than the solar wind are pulled along until they match the
solar wind’s speed.

Using data from solar-observing spacecraft, Gopalswamy and
his team discovered how much the solar wind sped up or slowed down
various Coronal Mass Ejections according to their initial speeds.
If the initial speed of a CME is known, the new model accurately
accounts for the influence of the solar wind on the CME speed, and
the CME arrival time at Earth can now be precisely estimated.

Images and more information related to this release can be
found on the Internet at:

http://www.lmsal.com/spd/Press/

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