ATLAS 3 Public Affairs Status Report #7 6:00 p.m. CST, Nov. 6, 1994 MET 2/7:00 Spacelab Mission Operations Control Marshall Space Flight Center Huntsville, Ala. ATLAS 3 instruments are wrapping up an extended period of atmospheric observations, and scientists at Spacelab Mission Operations Control are already seeing preliminary results from data obtained over the last three days. "As we do more missions, we get more experienced and more capable of doing real-time data processing," observed Mission Scientist Dr. Tim Miller. The Jet Propulsion Laboratory's ATMOS team reported interesting preliminary results of their observations inside the Antarctic polar vortex, an area of high-speed circulation over the South Pole. The circulation bottles up chemical constituents, making it something of a test tube where the atmosphere can be studied in isolation. "Our data show very low ozone levels over the Antarctic, as expected for this time of year," said ATMOS Principal Investigator Dr. Mike Gunson. "We also see evidence from certain long-lived gases that the air descended to lower altitudes as it cooled over the preceding winter period. This also was expected, but it is the first time it has actually been observed over such a broad range of altitudes." A "hole" in the ozone layer forms over the Antarctic around September each year, when increased springtime sunlight strikes air cooled during the Southern Hemisphere winter. The sun's ultraviolet radiation triggers chemical reactions that both create and destroy ozone. In recent years, human activity has introduced high levels of chemicals into the atmosphere which upset its natural balance. For instance, one free atom of chlorine released from chlorofluorocarbons can destroy thousands of ozone molecules. "By late November, ozone-rich air from the mid-latitudes mixes with the Antarctic air to fill in the lost ozone, and chemicals such as nitrogen oxides - - which act like a sort of atmospheric antacid -- begin to gobble up free chlorine, repairing the ozone loss," explained Gunson. In the winter, nitrogen oxides are frozen as nitric acid in ice crystals in polar stratospheric clouds. ATLAS 3 is flying during an intermediate period, when the ozone hole has begun to recover but before it has dissipated. Today's data indicate that nitrogen oxides are still very low. Chlorine measurements will be available in the next couple of days. During this morning's communications period with the free-flying CRISTA-SPAS satellite, the Middle Atmosphere High Resolution Spectrograph Investigation (MAHRSI) began taking readings of nitric oxide at high altitudes. The instrument previously had been making global readings of hydroxyl, and it will return to that mode during the next communications period. Both gases are active in the natural cycle of ozone chemistry. The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) continues to scan the atmosphere, making millions of spectra to map global locations and movements of some 15 trace gases. The huge number of observations is necessary because each cubic mile of atmosphere over the Earth is essentially its own separate chemical laboratory. For scientists to thoroughly understand chemical reactions and transport mechanisms like atmospheric winds, they must have extensive samples from as many latitudes, longitudes and altitudes as possible. The Shuttle Solar Backscatter Ultraviolet (SSBUV) experiment is finishing up its first period of atmospheric viewing, recording ozone levels and distribution for comparison with instruments aboard free-flying ozone-monitoring satellites. SSBUV is housed in two Get-Away Special canisters, mounted in the orbiter's cargo bay just in front of the ATLAS 3 Spacelab pallet. Data from the instrument is being relayed to the Goddard Space Flight Center in Greenbelt, Md., the instrument's home base, for preliminary analysis. The atmospheric observation period for the Shuttle-mounted instruments will end at about 6:30 p.m. CST. Then the orbiter will maneuver to relay communications between CRISTA-SPAS instruments and ground controllers for one orbit. Eight orbits of solar observations will follow.