The effects of wavebreaking and mixing barriers on quasi-horizontal transport and diffusion in the lower stratosphere are investigated with an isentropic Lagrangian transport model. Trajectories are computed using UKMO assimilated winds, and the dispersion statistics of ensembles of particles are analyzed.
The time dependence of the zonal and meridional ensemble variances can be approximated by power-laws at all latitudes. Anomalous (non-Gaussian) diffusion occurs both zonally and meridionally. Because motion across the vortex edge is inhibited by the strong mixing barrier, meridional mixing is generally subdiffusive, except far from the mixing barrier in the tropics. The zonal dispersion is superdiffusive inside the vortex and superballistic in the surf zone. The probability distribution functions of forward and backward zonal flight lengths can be described approximately by power-laws, indicating that the trajectories can be characterized as Lévy flights (i.e., random walks with divergent second moments). The relationship between the power-law exponents of the PDFs and the zonal variance exponent is discussed.
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12th Conference on Atmospheric and Oceanic Fluid Dynamics