Observations led by Southwest Research
Institute (SwRI) using NASA’s Imager for Magnetopause-to-Aurora Global
Exploration (IMAGE) spacecraft may lead to a new, critical technique for
monitoring and predicting space weather.

The team, including researchers from Los Alamos National Laboratory, used
the medium-energy neutral atom (MENA) instrument aboard the IMAGE satellite
to watch the first global images of the plasma sheet, a slab of plasma that
reaches tailward through the Earth’s magnetic field, or magnetosphere. The
observations revealed that the solar wind fills the sheet with high-density
plasma that is later squeezed toward the Earth when the interplanetary
magnetic field orientation points southward. These conditions correlate with
the occurrence of geomagnetic storms that create aurorae and have the
potential to disrupt ground-based electronic communications and harm
orbiting satellites.

“Space scientists had pieced together this concept based on single-point
measurements, but this is the first study that really lets us observe the
plasma sheet filling and emptying into the inner magnetosphere in response
to solar wind conditions,” says Dr. David J. McComas, executive director of
the SwRI Space Science and Engineering Division.

During a 20-day period, the team observed several geomagnetic storms.
Results indicate that the two most important factors to observe in order to
monitor and predict such storms are the orientation of the interplanetary
magnetic field (IMF) and the amount of material in the plasma sheet.

“When the plasma sheet is empty and the IMF is southward, nothing much
happens. When the plasma sheet is full and the IMF is northward, again,
nothing happens,” McComas says. “But when the plasma sheet is full and the
IMF turns southward, the plasma sheet pumps out its contents, and that’s
when things really start to get interesting around Earth.”

The space science community understood that a significant southward
interplanetary magnetic field is required to empty the plasma sheet to
create these storms. However, there had not been a way to measure the
fullness of the plasma sheet reservoir — until now.

SwRI managed the development of the IMAGE spacecraft and built the MENA
instrument in cooperation with Los Alamos. Since its launch in February
2000, the spacecraft has yielded the first global images of the Earth’s
magnetosphere, the region of space controlled by the Earth’s magnetic field.
Until IMAGE literally showed researchers the magnetospheric processes that
occur around Earth, scientists using single-point measurements from charged
particle detectors, magnetometers, and electric field instruments found it
difficult to piece together a bigger picture of the magnetospheric forces in
action. The Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS)
mission, slated for launches in late 2003 and 2005, will significantly
extend researchers’ ability to image the near space environment by providing
stereoscopic viewing of the magnetosphere for the first time.

IMAGE, a Medium-class Explorer mission, is managed by NASA Goddard Space
Flight Center in Greenbelt, Md. for the Office of Space Science in
Washington. SwRI has overall responsibility for IMAGE science,
instrumentation, spacecraft, and data analyses.

The paper, “Filling and Emptying of the Plasma Sheet: Remote Observations
with 1-70 keV Energetic Neutral Atoms,” by D.J. McComas (SwRI), P. Valek
(SwRI), J.L. Burch (SwRI), C.J. Pollock (SwRI), R.M. Skoug (Los Alamos), and
M.F. Thomsen (Los Alamos) appears in the Dec. 4, 2002, issue of Geophysical
Research Letters.

SwRI is an independent, nonprofit, applied research and development
organization based in San Antonio, Texas, with more than 2,700 employees and
an annual research volume of more than $319 million.