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Winter 2001

TIMED heads for the atmospheric frontier

by David Hosansky

Scientists are looking forward to fresh data following the launch of a new satellite expected to provide an unprecedented view of the mysterious upper regions of Earth's atmosphere. Launched on 7 December, TIMED (which stands for Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics) is designed to obtain a global picture of the atmosphere from roughly 60 to 180 kilometers (40–110 miles) above Earth's surface. Ground-based instruments can detect only a small portion of this complex region, and sounding rockets provide just a brief picture before falling back into the lower atmosphere.

"We're looking at weather at the edge of space," says Stanley Solomon, a principal TIMED investigator at NCAR's High Altitude Observatory. "This interface between what some people call the atmosphere and some people call space is an extraordinarily variable and dynamic region. I'm hoping to get a better understanding of how the Sun controls it."

Solomon and other researchers hope to use data from the NASA spacecraft to learn more about the temperature, wind, and chemical composition of the upper atmosphere. That could bolster communications networks, ensure that satellites stay on course, and provide scientists with greater insight into human influences on the atmosphere.

"There's never been a mission quite like this," says NCAR director Tim Killeen. "We're going to be looking at a fascinating part of the atmosphere, a real crossroads. TIMED will for the first time really probe that region by exploring the full range of atmospheric parameters—density, pressure, composition, vector winds, and other variables." These data, he adds, "will then allow us to establish a pole- to-pole climatology and really understand the region."

Killeen has been looking forward to the launch of TIMED since he chaired a working group of scientists that began designing the mission in the late 1980s. He is the principal investigator for TIDI, the TIMED Doppler Interferometer, which will measure globally the speed and direction of high-atmosphere winds. Other NCAR scientists working on TIMED include Alan Burns, Rolando Garcia, Maura Hagan, Roberta Johnson, Hanli Liu, Gang Lu, Daniel Marsh, Arthur Richmond, Raymond Roble, Anne Smith, and Qian Wu. According to Smith, one of the project's six interdisciplinary investigators, "We will

use numerical models in conjunction with the TIMED observations to investigate the physical mechanisms that affect energy and composition [within the region]."

The space economy

The region under scrutiny by TIMED has important impacts on orbiting vehicles and communications systems. When upper atmospheric temperatures rise, the resulting expansion pushes molecules to higher altitudes. This increased density exerts an added drag on satellites and slows down their orbits. Changes in the ionosphere can disrupt radio waves and affect the Global Positioning System. In addition, bursts of solar radiation can affect astronauts working on the space station.

"We have this large investment in a space-based economy," says Solomon, "and we have to have a better understanding of issues like the effects of atmospheric drag on orbits and the effects of the ionosphere on communications." Knowledge of the upper atmosphere lags behind that of the lower atmosphere by many decades, he adds. Scientists lack the data to provide satellite operators with even the crudest of forecasts about winds, temperatures, and other conditions.

"Right now, it's like where we were 50 years ago when nobody believed the weather forecasts," he explains. With TIMED, Solomon believes that scientists will move to nowcasting the upper atmosphere—that is, reporting with some accuracy on current conditions. In a few years, scientists may be able to provide the equivalent of one-hour forecasts.

"We'll make some really fundamental advances in understanding this region," he predicts. "Our goal is to take the next step from basic research to being able to provide possible societal benefits."

On the Web:

Just the facts

What: The TIMED (Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics) mission will study Earth's atmosphere about 40–110 mi (60–180 km) above the surface.

When: The TIMED satellite was launched on 7 December 2001 from Vandenberg Air Force Base, California. It will collect data on its 388-mi (625-km) circular orbit around Earth for two years. Another two years of data analysis will be supported by TIMED's operations and data centers at Johns Hopkins University.

How and who: Four instruments and associated teams, led by the principal investigators below, will probe the mesophere and lower thermosphere/ionosphere (MLTI).

  • GUVI: The Global Ultraviolet Imager is a spatial scanning ultraviolet spectrograph designed to measure composition and temperature profiles, as well as auroral energy inputs (Andrew Christensen, The Aerospace Corporation)

  • SEE: The Solar Extreme Ultraviolet Experiment consists of a spectrometer and a suite of photometers that will measure solar soft X-ray, extreme-ultraviolet, and far- ultraviolet radiation (Thomas Woods, University of Colorado)

  • TIDI: The TIMED Doppler Interferometer will measure the wind and temperature profiles of the MLTI (Tim Killeen, NCAR)

  • SABER: The Sounding of the Atmosphere using Broadband Emission Radiometry mission will measure pressure, temperature, key gases in the oxygen and hydrogen families, infrared cooling, and effects of solar and chemical heating of the MLTI (James Russell III, Hampton University)

Who else: More than 20 universities, laboratories, and research firms. Collaborators include Johns Hopkins University; the Universities of Alaska and Michigan; the University of California, Berkeley; Utah State University; Rostock University, Germany; and York University, Canada.

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Edited by Bob Henson, bhenson@ucar.edu
Prepared for the Web by Jacque Marshall
Last revised: Thu Dec 20 16:42:17 MST 2001