Key Investigator: Leonhard Pfister
This project seeks to determine how trace gases are exchanged between the lower atmosphere (the troposphere) and the upper atmosphere where the ozone layer is located (the stratosphere). This is critical to assessing the effects of natural and human-induced surface emissions on the potential for ozone depletion and global warming. To develop an understanding of transport processes in the lower stratosphere and at its lower boundary, specific scientific questions are addressed: (1) how does air move upward into the stratosphere in the tropics? (2) can these processes of upward movement explain the extreme dryness of the stratosphere? (3) what is the nature and importance of wave motions produced by rapidly rising air in the tropics? and (4) how does air move between the tropics and midlatitudes in the stratosphere?
As the illustration shows, natural emissions from oceans and lakes, as well as emissions resulting from human activities are produced at the earth's surface and injected into the stratosphere by cumulus clouds (left). Once in the stratosphere, these emissions can disturb the ozone layer. Large scale upward (stratosphere tropics) and downward (stratosphere midlatitudes) motions are driven by stratospheric wave motions, some of which are produced just above the cumulus clouds. Other wavelike motions are responsible for the transfer of air from the tropical to the midlatitude stratosphere. Stratospheric air is returned to the troposphere by folds in the stratosphere's lower boundary (right). All of these phenomena are of local to regional scale, making them ideal subjects for study by NASA's high altitude ER-2 aircraft.
The approach involves the analysis of ER-2 measurements from data obtained from the Stratosphere-Troposphere Exchange Project (STEP), with additional aircraft data from the Airborne Antarctic Ozone Experiment and the Airborne Arctic Stratosphere Expedition. So far, the data from STEP have (1) provided explanations for how tropical clouds move air from the troposphere to the stratosphere; (2) shown that the tops of these clouds are dry enough to account for low stratospheric humidities; (3) measured wavelike structures produced above tropical clouds; and (4) shown that other wavelike structures can move stratospheric air from the tropics to the midlatitudes.
MAP : RESEARCH SITES: Antarctica, Arctic, Australia, Chile, Iceland, Norway
COLLABORATORS: Australian Bureau of Meteorology, University of Washington, NOAA, Denver University, Jet Propulsion Laboratory, Particle Measuring Systems, Penn State University, University of Utah, Institut fur Chemie (W. Gerrnany), NCARR
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