Barotropic Instability of an Easterly Zonal Current

Abstract

As an extension of Nitta and Yanai (1969) the stability properties of a barotropic easterly current with a sine-profile jet are studied in more detail. The barotropic vorticity equation on a β-plane is solved by the finite difference method, as was made in the previous study. It is found that the stability properties of the easterly current are different from those of the westerly current in several respects such as a possibility of the existence of an unstable wave which propagates faster than a maximum velocity of an easterly current, the existence of many unstable waves of various meridional modes, strong dependency of wave properties on lateral boundaries, latitudinal profiles of wave amplitudes (as well as the direction of wave axis) and so on. It is also found that the β-plane approximation is justified only when we discuss two unstable waves of the lowest and second meridional modes.