Upper-level baroclinic instability

Effects on baroclinic instability of 'partial equilibration' and an Ekman lower boundary condition were examined by considering the linear stability of various zonal wind profiles having, as in the Charney (1947) problem, constant vertical shear and positive meridional gradient of potential vorticity aloft, but with reduced shear and zero or negative potential vorticity gradient at low levels. It is shown that, compared to the Charney problem, the partially equilibrated basic state zonal wind profiles obtained here have instabilities whose growth rates are less sensitive to the presence of an Ekman lower boundary condition.