We have examined meridional circulation of the atmosphere in terms of Hadley circulation in low latitudes and circulations associated with baroclinic waves in midlatitudes. Both circulations have a hemispheric one-cellular structure if viewed as transformed Eulerian mean or isentropic mean circulations. One-cellular circulation is directly described as a thermally driven circulation, and is also related to material transport in the Lagrangian sense. It must be remarked, however, that one-cellular circulation is not a static overturning flow. For instance, associated with baroclinic waves, latitudinally meandering flows along isentropic surfaces predominate at midlatitudes. One-cellular circulation of the atmosphere is characterized by these isentropic flows and cross-isentropic circulations in the meridional section. Isentropic flows are by definition adiabatic, while cross-isentropic flows are related to diabatic heating or cooling. The former results in isentropic mixing through north-south meandering air motions
KeywordsPotential Vorticity Meridional Circulation Diabatic Heating Hadley Circulation Extratropical Cyclone
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