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FLEET OF NASA SPACECRAFT OBSERVE ATMOSPHERE'S
RESPONSE TO RECENT SOLAR STORMS
Data on the Sun's activities during a recent series of
strong solar storms were gathered by an entire fleet of NASA's
Sun-Earth Connection spacecraft. The atmospheric data from
NASA's newest solar spacecraft, TIMED (Thermosphere,
Ionosphere, Mesosphere, Energetics and Dynamics), is providing
important new information on the final link in the Sun-Earth
Connection chain of physical processes that connect the Sun
and Earth.
"Several NASA spacecraft observed this strong activity
as it came from the Sun. Now TIMED provides the critical link
between what happened on the Sun and Earth's response," said
Sam Yee, leader of TIMED's science team, at the Johns Hopkins
University Applied Physics Laboratory in Laurel,
Md.
"TIMED allows us to observe the global reaction of our
upper atmosphere to solar activity," said Mary Mellott, TIMED
program scientist, NASA Headquarters in Washington. "One of
the important current puzzles for the Sun-Earth Connection
(SEC) community is determining why some solar activity has
significant geospace impact and some does not. Being able to
monitor the impact so well with TIMED should allow the
scientific community to make significant progress toward
solving this SEC mystery."
Along with TIMED, a fleet of observatories in space and
on the ground observed a powerful flare April 21 as part of
the Max Millennium program. The program, sponsored by NASA as
part of the Reuven Ramaty High Energy Solar Spectroscopic
Imager (RHESSI) mission, focuses on solar active regions with
the potential to produce storm activity. Every 24 hours, an
e-mail message with the current target is sent to
participating observatories so that coordinated observations
can be made.
The Transition Region and Coronal Explorer spacecraft
got a close-up look at the flare and its aftermath, while
RHESSI recorded flashes of X-rays that reveal impulsive
energy-release processes in flares, and the Solar and
Heliospheric Observatory (SOHO) got the big-picture view,
including the ejection of electrified gas clouds into space.
Additional observatories on the ground participated, like the
Nobeyama Radio Observatory, Nagano, Japan, which tracked radio
emission from the flare and its aftermath. Other spacecraft
near Earth, like the Advanced Composition Explorer (ACE), the
Imager for Magnetopause to Aurora Global Exploration (IMAGE),
and the Polar and Wind spacecraft, will be consulted to
determine the effects on the Earth.
"Detailed modeling using data from the many instruments
will take a long time, but it may help us in understanding the
basic processes at play during a solar explosion, called a
solar flare," said Stein Vidar Hagfors Haugan, a SOHO
scientist based at NASA's Goddard Space Flight Center,
Greenbelt, Md. "The idea is that observing more pieces of the
same picture is a lot better than observing the same number of
pieces of different pictures at different times."
Preliminary TIMED data will be featured in a special
session at the Spring 2002 American Geophysical Union meeting,
May 31, in Washington. TIMED, the first of NASA's Solar
Terrestrial Probes missions, began its science mission in
January 2002 and studies the influences of both the Sun and
humans on one of the Earth's least understood atmospheric
regions -- the Mesosphere and Lower Thermosphere/Ionosphere
(MLTI) -- the gateway between Earth's environment and space.
The MLTI region is located approximately 40-110 miles (60-180
kilometers) above the surface of the Earth.
Space weather in Earth's upper atmospheric regions can
affect satellite communications and orbital tracking,
spacecraft lifetimes and the reentry of piloted vehicles.
"When a change occurs in one region of our atmosphere, it
affects other regions," Yee says. "It's important that we
better understand how this gateway region responds to various
solar inputs, which affect our atmosphere's overall energy
balance."
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