Stratosphere-troposphere exchange and its specific features at extratropical latitudes

A review of the papers dealing with various aspects of stratosphere-troposphere exchange (STE) is presented. The development of STE concepts is described and quantitative estimates of STE obtained by different authors are given. Typical time scales and geographic features of STE are described. Special attention is given to the specific features of STE at extratropical latitudes where active vertical air transport is observed in both directions. The air ascent through the tropopause occurs there in the zones of warm conveyor belts, and the air descent takes place in the zones of stratospheric intrusions. Exchange processes in the key region including the upper troposphere and the lowermost stratosphere are described. The mechanisms of large-scale stratospheric intrusions in the systems of tropopause folds or cut-off lows are presented as well as the mechanisms of the mixing of the stratospheric air with the tropospheric one. Specific features of deep stratospheric intrusions are discussed which are based on the analysis of such indicators of stratospheric air as high concentrations of ozone and stratospheric radionuclide 7Be. Some aspects of stratosphere-troposphere energy exchange are considered.