Contact: Dane Konop                          FOR IMMEDIATE RELEASE                                                       
                                             5/16/97

The mixing of air in the upper levels of the Earth's lower atmosphere, the roughly seven-mile thick surface layer called the troposphere, is the key to understanding many of the problems such as global climate change -- vexing atmospheric chemists, according to a National Oceanic and Atmospheric Administration scientist.

In the current issue of Science magazine, J. D. Mahlman, director of NOAA's Geophysical Fluid Dynamics Laboratory in Princeton, N.J., examines many of the little understood mechanisms that control this mixing in the upper troposphere and the effects of this mixing on other atmospheric processes, including the impact of human sources of ozone and aerosols, the depletion of stratospheric ozone and the effects of emissions from subsonic aircraft.

"The upper troposphere is a transition zone separating the distinctly different chemistries of the stratosphere (the atmosphere 7-30 miles above the Earth's surface) from those of the lower troposphere. This region exchanges air with the stratosphere and the lower troposphere through various atmospheric transport processes," Mahlman explains.

"The effects of human-caused influences of ozone and aerosol concentrations in the upper troposphere are of current interest because of their potential contributions to climate change. For example, the sharp ozone losses observed in the lower stratosphere can influence chemical and climate changes in the upper troposphere by means of transport across the boundary between the troposphere and the stratosphere," Mahlman said.

A north-south "stirring" of the atmosphere by cyclonic weather systems outside the tropics may also explain the sharp, meandering and intermittent mid-latitude jet stream system that can be seen separating cyclones and anticyclones in geostationary satellite images.

Although global, 3-dimensional mathematical model runs by Mahlman and others have improved weather forecasts and climate simulations, Mahlman points out the chemical models depend on limited data from a small number of focused field experiments and on long-term measurements of chemicals in the atmosphere, wind, atmospheric pressure and temperature from to few locations.

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