Stratosphere exchange

The Lyman-a line also dissociates with H2O at altitudes between 80 and 85 km, where the supply of water vapor is maintained by methane oxidation even for very dry conditions at the tropospheric-stratospheric exchange region. An increase in HO c follows and thereby a sharp drop in the ozone concentration nears the meso-pause (Chapter 5.3.7 concerns stratospheric O3 cycles). The ozone concentration... 

Denmark 1.5 days after the explosion. Air samples collected at Roskilde, Denmark on April 27-28, contained a mean air concentration of 241Am of 5.2 pBq/m3 (0.14 fCi/m3). In May 1986, the mean concentration was 11 pBq/m3 (0.30 fCi/m3) (Aarkrog 1988). Whereas debris from nuclear weapons testing is injected into the stratosphere, debris from Chernobyl was injected into the troposphere. As the mean residence time in the troposphere is 20-40 days, it would appear that the fallout would have decreased to very low levels by the end of 1986. However, from the levels of other radioactive elements, this was not the case. Sequential extraction studies were performed on aerosols collected in Lithuania after dust storms in September 1992 carried radioactive aerosols to the region from contaminated areas of the Ukraine and Belarus. The fraction distribution of241 Am in the aerosol samples was approximately (fraction, percent) organically-bound, 18% oxide-bound, 10% acid-soluble, 36% and residual, 32% (Lujaniene et al. 1999). Very little americium was found in the more readily extractable exchangeable and water soluble and specifically adsorbed fractions. 

FIGURE 12.3 Schematic of wave-driven extratropical pump that drives global-scale transport from the tropical troposphere to the stratosphere and then poleward. Three possible paths for stratosphere-troposphere exchange (STE) are shown. (Adapted from Holton et al., 1995.)... 

In short, exchange of air between the Northern and Southern Hemispheres is slow, as is that between the troposphere and stratosphere, both being on the time scale of about a year (Warneck, 1988). The mechanisms of stratosphere-troposphere exchange are complex but a detailed understanding of these is critical to the assessment of the atmospheric fates of many species, particularly those emitted in the lowermost stratosphere. For reviews of these processes, see Holton et al. (1995), Salby and Garcia (1990), and Mahlman (1997) and for some relevant studies, Langford et al. (1996) and Folkins and Appenzeller (1996). 

Lelieveld, J., B. Bregman, F. Arnold, V. Burger, P. J. Crutzen, H. Fischer, A. Waibel, P. Siegmund, P. F. J. van Velthoven, Chemical Perturbation of the Lowermost Stratosphere through Exchange with the Troposphere, Geophys. Res. Lett., 24, 603-606 (3997). 

The pattern and rate of exchange of stratospheric air with the mesosphere, with the troposphere, and between hemispheres is still poorly known. Within the stratosphere a complex pattern of eddy mixing and mean motions governs the redistribution of trace constituents. In the lower stratosphere the adsorption or attachment of trace constituents to natural sulfate particles influences their subsequent transport. Some main features in stratospheric transport processes based on tracer studies are reviewed here. 

A second issue is the transport of trace gases in the stratosphere. How do the polar vortices form How readily are air parcels exchanged between the vortex and midlatitudes and between altitudes at different latitudes and seasons What are the diabatic heating and cooling rates at different times... 

MODEL ANALYSIS OF STRATOSPHERE-TROPOSPHERE EXCHANGE OF OZONE AND ITS ROLE IN THE TROPOSPHERIC OZONE BUDGET... 

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