UniSci Daily
Researchers
at The Johns Hopkins University Applied Physics Laboratory, Laurel,
Md., (APL) are now able to simultaneously measure the magnetic
and electrical fields over large areas of the ionosphere above
the Earth's polar regions, providing the first continuous monitoring
of electric currents between space and the upper atmosphere and
generating the first maps of electric power flowing into the polar
upper atmosphere.
These advances will allow greatly improved understanding and forecasting
of global space weather and help prevent disruption of communication
and power systems when electromagnetic storms strike the nation.
The work,
sponsored by the National Science Foundation, makes use of magnetometers
carried on each of the 66 satellites of the Iridium System satellite
constellation operating as a global satellite communications network.
Circling the globe in 470-mile-high, polar orbits, they are providing
continuous measurements of the magnetic fields above the Earth's
poles.
Scientists
at JHU/APL have developed techniques to extract the signatures
of electrical currents flowing between the atmosphere and space
from the magnetic field readings. Maps of the electric current
in space are then constructed in much the same way that normal
weather maps are made from weather station readings.
At the same
time, SuperDARN - the Super Dual Auroral Radar Network, a
multinational network of a dozen radars spread around the poles
to study the ionosphere, sponsored by NSF and NASA and led by
APL scientist Dr. Raymond A. Greenwald - is bouncing radar
signals off the same regions to measure the electric field and
its minute-by-minute variations.
"By combining
Iridium System and SuperDARN data, we're able for the first time
to continuously map the powerful currents flowing between space
and the Earth's upper atmosphere," says Brian J. Anderson,
who leads APL's research effort. "This is a major achievement
because monitoring this environment is extremely difficult due
to its enormous volume, which can vary by a factor of 10 in one
hour. The Iridium orbits are ideal for monitoring this big system
because the current is funneled to the polar regions, where the
satellites detect it."
Based on extensive
experience working with magnetic field data from satellites, APL
scientists were able to develop sophisticated signal processing
techniques for automatically extracting needed signals from Iridium
data so they could be combined in a useful way with SuperDARN
data. "This was an essential part of the effort," says
Anderson. "With so many satellites involved, any hands-on
analysis of the data would have been impossible."
The maps of
electrical current show dramatic shifts due to changes in the
solar wind. These results will allow scientists to test computer
models of Earth's space environment far more accurately and exhaustively
than ever before. Preliminary maps of the power flow have revealed
"hot spots" of energy flowing into the atmosphere at
high altitudes, creating pockets of hot air that rise and create
drag on spacecraft flying through them at altitudes below 300
miles.
"Timely,
accurate space weather forecasts will give advance warning of
electromagnetic storms that in the past have shown their ability
to disrupt communications, degrade GPS accuracy, cripple electrical
power grids, and menace astronauts, satellites and aircraft with
dangerous levels of radiation," says Anderson.
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