A Numerical Study of the Three-Dimensional Structure and Energetics of Unstable Disturbances in Zonal Currents: Part I

Abstract

Abstract The dynamic instability properties and the structure and energetics of unstable disturbances in both pure baroclinic and pure barotropic zonal currents are investigated by applying an eigenvalue technique to the finite-difference version of a linear quasi-geostrophic model. Numerical results are compared with well-known theoretical results. Their accuracy is also examined by varying the number of subdivisions. It is found that the numerical method gives sufficiently accurate results, particularly in describing the structure and energetics of the primary, unstable, cyclone-scale disturbances. In the baroclinic case, the unstable waves produce northward and upward transports of sensible heat. These conversion rates are pronounced in the lower layer. The short waves are characterized as shallow waves, the long waves as upper waves. The symmetric perturbations in the barotropic cosine-jet current are unstable for intermediate wavelengths, while the antisymmetric perturbations are stable. The barotrop...