Results could lead to improved satellite transmissions

WESTFORD, Mass. — “Following scattered solar explosions, we’re in for
some severe space weather over most of North America.”

It’s not your typical forecast, but owners and operators of the
hundreds of active satellites would be very interested in hearing it.
Using ground-based instruments, Massachusetts Institute of Technology
researchers can now provide real-time images of space weather — a
new view of the same information NASA gets from space-based sensors
looking back at the Earth. The work, by scientists at MIT’s Haystack
Observatory and Lincoln Laboratory, will appear in an upcoming edition
of the American Geophysical Union’s Geophysical Research Letters (GRL).

It also will be featured at a NASA Space Science Update on May 9 as
NASA headquarters in Washington, DC.

Unexpected disturbances in the plasmasphere — the cloud of charged
particles extending 10,000-plus miles above Earth — affect satellite
transmissions and result in damage to satellites and spacecraft.
Satellite communications are used for everything from TV to military
operations such as locating soldiers in Afghanistan or steering tanks
during a sandstorm.

“The ionospheric radar measurements from Haystack show how space
weather effects far out in the magnetosphere are directly connected
to the upper atmosphere, where they can disrupt systems such as GPS
(Global Positioning System),” said James Burch of Southwest Research
Institute of San Antonio, TX, a principal investigator for NASA.

“Phenomena known as plasmaspheric tails that develop during magnetic
storms were thought to be relatively benign, but the Haystack
observations have shown that in fact they have strong ionospheric
effects,” he said.

“What we see goes far beyond our wildest expectations,” said John
C. Foster, associate director of Haystack and lead author of the
upcoming paper. “We are looking with new eyes, ground-based eyes, at
the phenomena that give us space weather effects. We are just at the
beginning of a very rich area for research.”

JOINING FORCES

Pairing information gleaned from hundreds of special dual-frequency
GPS receivers with data from Haystack’s ionospheric radar,
researchers at MIT were able for the first time to map the ever-
changing plasmasphere from the ground.

In addition to Foster, authors of the GRL paper are Philip J.
Erickson, research scientist with Haystack’s Atmospheric Sciences
Group; Anthea J. Coster, technical staff member at the Lincoln Space
Surveillance Complex, MIT Lincoln Laboratory; Jerry Goldstein of Rice
University in Houston and Frederick J. Rich of the Air Force Research
Laboratory at Hansc:lÎ8ield, Lexington, Mass.

The researchers say they have achieved a breakthrough in using new
methods to study and map the Earth’s atmosphere, with results directly
applicable to the very young field of space weather prediction.

“The scientific and applications interests overlap,” Foster said.
“With our GPS maps and the high-altitude NASA imagery, we can
construct a global picture of the plasmasphere. Detailed low-altitude
radar and satellite observations then guide our interpretation of the
physics involved. By putting together multiple views, we can come up
with a consistent picture.”

HEAVY WEATHER

The Earth is rotating under an ever-changing system of interacting
electric and magnetic fields, electric currents and charged particles
called the magnetosphere. Ionization of our upper atmosphere by
ultraviolet sunlight produces a plasmasphere nearest the Earth. Here,
particles are a cold, dense mixture of electrons and ions called a
plasma. Based on local conditions, the plasma can be dense with
electrons or diffuse.

The magnetosphere provides a barrier to the solar wind, which
explodes earthward from the sun’s outer atmosphere during violent
solar storms. These outbursts result in dramatic changes through the
geospace environment.

Plasmaspheric tails — long plumes with increased electron
concentrations — can result. Radio waves originating on the ground
can move through homogenous areas easily, but the edge of the tails,
where low- and high-density areas of electrons collide, is like a
brick wall to radio waves.

This disrupts satellite transmissions, but “knowing there is a
problem (such as the location of a plasmaspheric tail) allows the
user to change to another communications link,” Erickson said.

SCANNING THE SKIES

Haystack’s Millstone Hill radio antenna in Westford, Mass., looks like
a giant metal spider web. Its large size, combined with sensitive
receivers and a powerful transmitter, provides researchers with
detailed diagnostics of the charged upper atmosphere from the ground.
The only system of its kind in the continental United States, it is
in a prime location to monitor space weather over eastern North
America.

Lincoln Laboratory has been pursuing GPS ionospheric investigations
since 1985. Precise knowledge of the ionosphere is critical to
accurately track Earth-orbiting satellites.

“These MIT programs provide a unique environment for combining basic
and applied research. People doing GPS need to know about the physics,
and people doing the physics need GPS to understand what they are
seeing,” Foster said.

“The research community can now unify disparate things they’ve seen
in one explanation,” said Erickson. “That’s the real power of this.”

This work is funded by the National Science Foundation through a
cooperative agreement with MIT and by the U.S. Air Force.

[NOTE: Images supporting this release are available at
http://web.mit.edu/newsoffice/nr/2002/spaceweather.html]