Abstract
Abstract The hydrodynamic instability characteristics of planetary zonal flows are investigated through use of a quasi-geostrophic numerical model of high spatial resolution. An initial-value technique is employed to obtain solutions of the linear problem. Certain zonal flows containing both vertical and lateral shears, which are representative of those observed in the earth's atmosphere, are found to be unstable with respect to the large-scale quasi-geostrophic disturbances. Westerly currents, each characterized by a latitudinally symmetric jet containing absolute vorticity extrema at various latitudes, amplify perturbations of some scales through a dominating baroclinic mechanism, and amplify perturbations of other scales through a dominating barotropic mechanism. For these flows, the unstable perturbations of relatively short zonal wavelength convert zonal available potential energy into perturbation energy and simultaneously strengthen the zonal kinetic energy of the basic flow. On the other hand, the...
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