A high-resolution two-dimensional spherical model is used to investigate the fundamental process of large-scale horizontal mixing in and out of the circumpolar vortex in the winter stratosphere. Concept and analysis method of the chaotic mixing, which were first introduced to geophysical flow by Pierrehumbert(1991) with a simple kinematical model, are applied to some quasi-periodic and nonperiodic solutions obtained in the dynamical model.
Ishioka and Yoden(1995) obtained quasi-periodic and nonperiodic solutions in an idealized stratospheric model of two-dimensional non-divergent fluid with zonally symmetric zonal-flow forcing and Newtonian-type damping. The forced flow is a barotropically unstable polar-night jet and the obtained solutions mimic the eastward traveling planetary waves in the southern hemisphere upper stratosphere. Some of the typical solutions are analyzed in this study.
Poincare sections for several particles are used to distinguish the regions of chaotic mixing. Dispersion of lots of particles placed in an limited area in the chaotic region shows the characteristics of two-dimensionalization from large scales; fractal dimension (correlation dimension) is estimated to describe the time dependence of the mixing process quantitatively. Stagnation points in the streamfunction field in the co-moving frame with the dominant wave play an important role in the chaotic mixing. Finite-time Lyapunov stability analysis gives a quantitative confirmation of the role.
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12th Conference on Atmospheric and Oceanic Fluid Dynamics