Horizontal Energy propagation in a Barotropic Atmosphere with Meridional and Zonal Structure

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  • 1 National Center for Atmospheric Research, Boulder, CO 80307
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Abstract

To investigate how the propagation of energy away from steady sources may be influenced by the horizontal structure of the time-averaged flow in the troposphere, solutions to a barotropic model are displayed and interpreted. The model is steady and linearized about a basic state which varies in latitude and longitude. Emphasis is placed on cases where the longitudinal variations are gradual.

Many of the results can be analyzed by locally applying tools developed for zonally symmetric basic states, e.g., ray tracing and refractive indices. Simple background flows are constructed which have longitudinally confined critical lines, reflective surfaces, wave guides, and regions conducive to propagation. An example is given in which longitudinal derivatives of the basic state are significant. The theory of ray tracing in a two-dimensional wind must be employed as an interpretive tool in this case. It is concluded that zonal variations tend to enhance poleward (equatorward) propagation in large-scale troughs (ridges).

Examples are also shown of propagation through observed January 300 mb mean flow. These experiments suggest that the southern flank of the Asiatic jet may act as a partial reflector, increasing the likelihood of resonance in the midlatitudes. The central tropical Pacific appears to have potential as a corridor for inter-hemispheric transmission, though during typical January conditions wavetrains emanating from the mid-latitudes are absorbed there.

Abstract

To investigate how the propagation of energy away from steady sources may be influenced by the horizontal structure of the time-averaged flow in the troposphere, solutions to a barotropic model are displayed and interpreted. The model is steady and linearized about a basic state which varies in latitude and longitude. Emphasis is placed on cases where the longitudinal variations are gradual.

Many of the results can be analyzed by locally applying tools developed for zonally symmetric basic states, e.g., ray tracing and refractive indices. Simple background flows are constructed which have longitudinally confined critical lines, reflective surfaces, wave guides, and regions conducive to propagation. An example is given in which longitudinal derivatives of the basic state are significant. The theory of ray tracing in a two-dimensional wind must be employed as an interpretive tool in this case. It is concluded that zonal variations tend to enhance poleward (equatorward) propagation in large-scale troughs (ridges).

Examples are also shown of propagation through observed January 300 mb mean flow. These experiments suggest that the southern flank of the Asiatic jet may act as a partial reflector, increasing the likelihood of resonance in the midlatitudes. The central tropical Pacific appears to have potential as a corridor for inter-hemispheric transmission, though during typical January conditions wavetrains emanating from the mid-latitudes are absorbed there.

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