The effects of latitudinal asymmetries on baroclinic instability

Abstract

Baroclinic instability of zonal flows with different latitudinal structures is examined, using a linear, quasi‐geostrophic two‐level ß‐plane model. The flows have different amounts of skew, with respect to the channel centre, at different vertical levels. The results are interpreted in terms of the instability of the baroclinic components of the zonal flows. Because of the presence of latitudinal asymmetries, a spectrum of meridional modes is generated in the perturbation. In general, the meridional spectrum has two peaks: a primary peak at the planetary basic flow scale, and a secondary peak near the radius of deformation. As neutral stability is approached, the latter scale becomes more important, i.e. there is a tendency for more small‐scale structure near neutral stability. The perturbation zonal scale is close to the radius of deformation. The eddy amplitudes and momentum fluxes are also examined. The case that best applies to the atmosphere is also discussed.