The typical tropospheric state can be simply characterized as a well-mixed PV layer with disturbances that are localized at upper levels near the tropopause. Here, we present several models for understanding a well-mixed troposphere based upon the idea of a uniform PV fluid whose balanced motions are primarily controlled by a tropopause boundary condition.

The most investigated of such uniform PV dynamics is surface quasigeostrophy (sQG) as in Blumen (1978) and Held, etal (1995). Inclusion of finite Rossby number corrections have produced the realistic vortex asymmetry to intense and localized cyclone development. Introducing a finite depth to the layer naturally produces a dynamics whereby larger horizontal scales (with deeper vertical structure) behave in an increasingly barotropic manner. Finally, a modification of the tropopause boundary condition to mimic a free-surface provides a bridge to explaining why shallow-water models produce significantly different vortex asymmetries (Polvani, etal 1994).