A Nonlinear Model of the Time-Average Axially Asymmetric Flow Induced by Topography and Diabatic Heating

Steven Ashe National Center for Atmospheric Research, Boulder, CO 80307

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Abstract

Solutions are obtained for spectrally truncated, two-layer, stationary asymmetric flow on a hemisphere. This flow results from nonlinear perturbations of a prescribed meridionally nonuniform, axially symmetric zonal flow by a stationary distribution of diabatic heat sources and sinks and by deflection of the flow by topography.

The model has wavenumber response properties that differ from analogous linear beta-plane models and it is more stable to parameter variations.

The model is run for January and July conditions. Series of January and July atmospheric observations are reduced to a spectrally truncated, two-layer form. These data are used to assess the model solutions and to assign zonal state and forcing fields. The response in the upper-layer velocity fields and in the temperature fields away from the equator compares favorably with observations. A comparison is made with the linearized solution; inclusion of the nonlinearities improves placement of those flow features associated with the thermodynamic effect of the Kuroshio Current in winter.

Abstract

Solutions are obtained for spectrally truncated, two-layer, stationary asymmetric flow on a hemisphere. This flow results from nonlinear perturbations of a prescribed meridionally nonuniform, axially symmetric zonal flow by a stationary distribution of diabatic heat sources and sinks and by deflection of the flow by topography.

The model has wavenumber response properties that differ from analogous linear beta-plane models and it is more stable to parameter variations.

The model is run for January and July conditions. Series of January and July atmospheric observations are reduced to a spectrally truncated, two-layer form. These data are used to assess the model solutions and to assign zonal state and forcing fields. The response in the upper-layer velocity fields and in the temperature fields away from the equator compares favorably with observations. A comparison is made with the linearized solution; inclusion of the nonlinearities improves placement of those flow features associated with the thermodynamic effect of the Kuroshio Current in winter.

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