DYNAMICS OF TRANSPORT PROCESSES IN THE UPPER TROPOSPHERE

A number of key problems in atmospheric chemistry are shaped by the st rength and character of the various mechanisms acting to move and mix air in the upper troposphere. These transport processes are examined f rom a mechanistic perspective, with primary emphasis on the tropopause and middle-troposphere regions in the extratropics. The roles of vert ical and horizontal transport ''barriers'' are explored, including the processes by which such barriers are created and are overcome. These transport considerations lead to a hypothesis concerning the processes that shape the tropopause itself. Some perspectives are offered on th e still immature subject of transport in the upper troposphere of the tropics.