Statistics
Scientific paper
Jan 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt.......128p&link_type=abstract
Thesis (PH.D.)--YALE UNIVERSITY, 1992.Source: Dissertation Abstracts International, Volume: 53-12, Section: B, page: 6354.
Statistics
Planetary Waves
Scientific paper
Recent analyses of atmospheric data have indicated that the amplitude of atmospheric waves of planetary scale can switch from a mode of large amplitudes to a mode of small ones and vice versa. This behavior is present in both, the Northern and Southern Hemispheres. We describe these observations and situate them in the context of low -frequency, intraseasonal variability. Most theories of bimodality rely on the presence of an extratropical source of long Rossby waves and on their interaction with the forcing in order to achieve a resonance in the response of the planetary flow. We demonstrate the incompatibility of these theories with the observations characterizing global weather regimes. Then, we develop a hierarchy of numerical, quasi-geostrophic models in order to determine the simplest model containing the minimal physics sufficient for generating bimodal statistics for the planetary waves. The physical properties which allow the production of bimodal dynamics relate to the stability characteristics of the models' stationary solutions and to the zonal wavenumber(s) at which the lower boundary is felt. The latter is not a major catalyst for the appearance of dynamical instabilities in spectral models retaining a large number of components in the truncation, contrary to the results from low-order ones. Instabilities and bimodality appear in our model when it is run with no lower -boundary forcing. Asymmetries in the latter actually supply a phase-locking mechanism favoring the establishment of standing oscillations. The validity of models with channel geometry has been questioned on the ground that they would allow for resonant behavior by preventing latitudinal wave propagation. We study the problem of the dispersion of perturbation energy across parallels of latitude from a source embedded in a fluctuating zonal-mean flow, using a linearized, non -divergent, barotropic vorticity equation and a basic zonal -mean flow constructed from atmospheric data. We find that the spatial fluctuations of the basic zonal flow can offer a localizing mechanism that acts to confine wave propagation to a certain latitude band around the source of perturbation energy. The critical parameters characterizing the wave as propagating or confined consist of the amplitude and meridional scale of the fluctuations.
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