Upper-level baroclinic instability

We examine some of the effects of "partial equilibration' and an Ekman lower boundary condition on baroclinic instability by considering the linear quasi-geostrophic stability of two classes of zonal flows. These flows, which are simple models of the partially equilibrated basic states that may result when a growing baroclinic wave modifies the constant shear zonal wind profile of the Charney problem, have reduced vertical shear and negative or zero potential vorticity gradients at low levels. The unstable eigenmodes of increasingly equilibrated zonal wind profiles have, in general, increased amplitudes in the mid- and upper troposphere, and the growth rates of these instabilities have decreased sensitivity to the presence of an Ekman lower boundary condition. -from Authors