Troposphere exchange

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). 

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

Holton, J.R., and Lelieveld, J. (1996) Stratosphere-troposphere exchange and its role in the budget of tropospheric ozone, in P.J. Crutzen and V. Ramanathan (Eds.), Clouds, Chemistry and Climate, NATO ASI Series, Springer-Verlag, Berlin, pp. 173-190. 

Vaughan, G. (1988) Stratosphere-troposphere exchange of ozone, In I.S.A Isaksen (Ed.) Tropospheric ozone, D. Reidel, Dordrecht, pp. 125-135. 

Kentarchos, A.S., Roelofs, G.J., and Lelieveld, J. (1999) Simulation of extratropical synoptic scale stratosphere-troposphere exchange using a coupled chemistry-GCM Sensitivity to horizontal resolution, submitted to J. Atm. Sci. 

Danielsen E.F., Stratospheric tropospheric exchange based on radioactivity, ozone, and potential vorticity. J. Atmos. Sci., 25, 4495-4498 (1968). 

Semb, A. Proc. WMO svmp. lonq-ranae transport of pollutants and it relation, t.9 qeney l ciiculfttioh jnsiuging stratospheric/tropospheric exchange process. WMO No. 538, pp. la-lm, Geneva, 1979. 

Figure 3.30. Schematic representation of the atmospheric circulation (arrows) and associated quasi-horizontal mixing between the surface and the middle stratosphere. Mixing processes leading to stratosphere-troposphere exchanges are also represented. The heavy vertical lines denote dynamical barriers against meridional transport. Note the large-scale ascent in the tropical stratosphere above intense convective systems in the tropical troposphere, and large scale descent associated with the polar vortex during winter (WMO, 1999).

Reiter, E. R., M. E. Glasser, and J. D. Mahlman (1969). The role of the tropopause in stratospheric-tropospheric exchange processes. Pure Appl. Geophys. 12, 183-221. 

Similar to diurnal variation, seasonal variation is driven by photochemical ozone production with a maximum in summer. The winter minimum represents a reduced photochemical activity (Fig. 2.85) but might also show the chemical ozone depletion into cloud droplets. As seen in Fig. 2.85, daily variation might even be larger because of changes in the air masses with different characteristics in ozone production and depletion. Differences from year to year depend on the large-scale weather situation as well as varying stratosphere-troposphere exchange processes (STE),... 

The O2 photodissociation and subsequent O3 formation in the lower stratosphere is the most important source of O3 in the troposphere via the stratosphere-troposphere exchange. The tropospheric net O3 formation (Chapter 5.3.7) is another important source, especially because of anthropogenic enhancement. Fig. 5.6 shows all principal oxygen reactions note that O2 photolysis can be excluded in the climate system in the more narrow sense close to the earth s surface. The exit pathways (sinks) to products (Fig. 5.6) are only possible if there are additional elements and compounds (Chapter 5.3.2.2). In a pure oxygen gas system, we only consider four reactions (5.5, 5.6, 5.13 and 5.14), forming a steady state ... 

The cumulative deposition of anthropogenic radionuclides shows a typical latitudinal distribution, with high levels in the mid-latitude regions of the Northern Hemisphere, reflecting the stratosphere-troposphere exchange of air masses in the mid-latitude region (UNSCEAR 2000a). 

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