Unstable Baroclinic Modes Damped by Ekman Dissipation

Abstract

Inclusion of Ekman damping in baroclinic models severely limits the range of unstable wavenumbers as well as the growth rate of the instabilities that remain. In contrast, there is much less reduction by the same dissipation of the transient growth of perturbations chosen to resemble those associated with observations of the initial stages of cyclogenesis. It is shown here that the Charney problem with Ekman dissipation included provides a realistic model of damped instability, that the growth rates of the unstable waves are small compared both with observed deepening rates and with deepening rates for initial value problems, and that vertical discretization is likely to produce spurious instabilities in damped models.