Quasigeostrophic diagnosis of three-dimensional ageostrophic circulations in an idealized baroclinic disturbance

Keyser et al.'s (1989) kinematic technique for the representation of 3D vertical circulations in baroclinic disturbances in terms of a vector eigenfunction, the 'psi vector', is presently projected onto the framework of quasi-geostrophic (QG) theory. The projection of the psi-vector equation onto the cross-front vertical plane leads to a generalization of the QG form of the Sawyer-Eliassen equation that is applicable to 3D flows. The diagnostic methodologies for the total ageostrophic flow and for the generalized Sawyer-Eliassen equation are illustrated by applications to upper-level and surface frontal zones that are simulated in an f-plane primitive equation channel model of a finite-amplitude baroclinic wave.