理想的および現実的な東西非一様流におけるロスビー波の伝播

Abstract

The Rossby wave propagation in various basic flows is studied, based on the numerical time-integration of a barotropic model on the sphere.First, the propagation in idealized basic flows is examined. When the zonally uniform basic flow has a strong jet, the jet stream acts like a waveguide for the Rossby wave. When the basic flow has a component of zonal wavenumber 1 (or 2), the Rossby wave emanating from the entrance region of the jet rapidly propagates eastward to the jet exit region. Then, the wave becomes stagnant and its amplitude is increased in the exit region. When the wave component superposed in the basic flow is strong, the basic flow has barotropically unstable modes. Nevertheless, this instability is weak so that the propagation patterns are not influenced by it. The barotropic conversion of kinetic energy from the basic field is evaluated to be important in this wave amplification in the jet exit region. Then, it can be understood that this wave amplification is produced both by the stagnation of wave energy from the energy source and by the subsequent barotropic conversion in the jet exit region.Second, the wave propagation is examined for monthly-mean basic flows derived from wintertime observational data. It is found that the propagation property of the Rossby wave is highly dependent on the basic wind distribution. In one case (December 1986) the Rossby wave, which has propagated eastward through the Asian jet, is blocked and becomes stagnant near the jet exit region. In contrast, in the other case (January 1984) near the jet exit the propagation path splits into eastward and equatorward paths.