Stratosphere/Troposphere exchange - The exchange between the stratosphere and the troposphere is extremely important. It is caused by upwelling in the troposphere and when troposphere species are pushed into the stratosphere. It starts in the tropics and moves toward the poles. If certain ozone destroying species are brought into the stratosphere from the troposphere when they mix damage to the ozone layer and global warming can result.
[Hall, Timothy M.and Mark Holzer. Adjective-diffusive mass flux and implications for stratosphere-troposphere exchange. Geophysical Research Letters, Vol, No. , Pages 1—4]
[Gettelman, Andrew and Adam H. Sobel. Direct Diagnoses of Stratosphere—Troposphere Exchange. Journal of Atmospheric Sciences. Vol. 57:1] 
Atmospheric Chemistry Glossary