A Numerical Study on the Maintenance of Weather Regimes and their Transitions

点击翻译按钮获取中文摘要

The main purpose of the present study is to clarify the mechanisms of the maintenance of weather regimes and and transitions between them by using idealized full-nonlinear numerical models. Our final goal is a complete dynamical understanding of low-frequency variability in the troposphere in the light of multiple weather regimes and their transitions.A highly-truncated barotropic model of the atmosphere introduced by Legras and Ghil (1985) was used to study the dynamical structure of weather regimes and their relationship to the temporal variation of predictability. The model is a low-order spectral model of 25 variables which includes the effects of zonal-flow forcing, dissipation and surface topography. Dynamical properties of the attractor of the model was investigated to show the role of quasi-steady states (i.e., weather regimes). Intensity of the zonal-flow forcing was changed as an experimental parameter. A finite-time Lyapunov stability analysis was also done for several examples of the attractors to show the relationship between the quasi-steady states and predictability.A global primitive-equation model of the atmosphere was used to study nonlinear interactions between mean zonal flow and baroclinic disturbances. Internal non periodic variation is found in long-time integrations of the model under a perpetual condition. The variation is characterized by irregular transitions between two preferred regimes of double-jet and single-jet of mean zonal flow. A PV-rheta analysis was done for two extreme periods of these regimes and two different patterns of the life-cycles of extra-tropical cycles were obtained in the corresponding regimes. A statistically significant relationship was also obtained between the zonal flow regimes and the patterns of the extra-tropical cyclones.