Web Extra   December 18, 2001

Lighting up the atmosphere

A Russian Space Agency Meteor-3M spacecraft aboard a Ukrainian Zenit-2 rocket successfully lifted off Dec. 10 from Kazakhstan, carrying a payload that will collect more data for atmospheric scientists.

SAGE III, the second launching of the Stratospheric Aerosol and Gas Experiment, is now in orbit and measuring how sunlight and moonlight travel and bend through Earth's atmosphere. The measurements help atmospheric researchers understand the variation of aerosol concentrations in the middle atmosphere. These variations play a role in climate and in the depletion of ozone.

SAGE III follows on the heels of SAGE II, which has been orbiting Earth since 1984. SAGE III will orbit high latitudes, as does SAGE II, but will make more detailed measurements than SAGE II. It can also measure lunar occultation, which means watching aerosols that can’t exist in sunlight. One example is nitrogen trioxide, an important factor in ozone depletion, says Chip Trepte, the deputy project scientist for the SAGE III, which is managed by the NASA Langley Research Center in Hampton, Va. The project uses the Russian spacecraft and Ukrainian rocket as part of an international collaboration, he says.

“There are subtle changes in the atmosphere,” Trepte says. “The question you have at any given time is which process tends to dominate. That’s why it’s important to measure a variety of different species in the atmosphere to measure ozone.”

SAGE III will make a vertical profile of ozone, nitrogen dioxide, water vapor, temperature and pressure, and aerosols as high as 85 kilometers in the atmosphere.

Volcanologists can also use the data to study the distribution of aerosols after volcanic eruptions. Alan Robock of Rutgers has been studying how aerosols released during the 1991 eruption of Mount Pinatubo have changed regional climate patterns. SAGE III will be an important instrument, he says. At the same time, he adds that, because SAGE II and SAGE III together mainly orbit near the poles, the tropical latitudes remain unmonitored. “There’s a hole in the most interesting part: the equator,” Robock says.

Trepte adds that a SAGE III instrument should be deployed aboard the International Space Station by 2005 and will monitor latitudes closer to the equator.

Kristina Bartlett

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