Transport Processes in the Stratosphere and Troposphere
Transport of air across the tropopause plays an important role in determining the chemical composition, and hence radiative properties, of both the troposphere and stratosphere. Quantifying this transport presents a significant challenge on account of the many multiscale processes involved from the global scale mean meridional circulation, through intermediate advective and convective processes, to molecular diffusion. It has long been recognized that tropospheric air enters the stratosphere principally in the tropics, and moves poleward in the stratosphere.
To understand the large-scale circulation in the troposphere and stratosphere, it is useful to look at transport processes averaged around a latitude circle. Ozone productionmainly takes place in the tropical stratosphere as the direct solar radiation photodissociates oxygenmolecules (O2) into oxygen atoms (O), which quickly react with other O2 molecules to form ozone (O3). But most ozone is found in the higher latitudes rather than in the tropics, i.e., outside of its natural tropical stratospheric source region. This higher-latitude ozone results from the slow atmospheric circulation that moves ozone from the tropics where it is produced into the middle and polar latitudes. This slow circulation is known as the Brewer-Dobson circulation.
KeywordsRossby Wave Planetary Wave Polar Vortex Lower Stratosphere Hadley Circulation
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