Suppression of baroclinic instability in horizontally sheared flows

Abstract

Baroclinic instability in the presence of a meridionally sheared barotropic component to the basic flow is studied using a two-level model. The inclusion of a linear shear results in meridionally confined normal modes with growth rates much reduced compared to the unsheared case. Similar results hold for more complicated situations, such as a baroclinic jet with barotropic shear. The results are applied to life cycle calculations in which it is shown that the nonlinear decay phase of a baroclinic disturbance sets up barotropic shears which tend to suppress further baroclinic developments. An example of the Southern Hemisphere winter mean flow is found to be strongly stabilized by virtue of a strong sheared barotropic part of the zonal flow. -Author