Rossby wave radiation from an eastward jet and its recirculations
A series of numerical experiments is carried out to investigate in detail the properties of the variability radiated from a baroclinic jet and its recirculations. Driven by an inflow from the western boundary, an eastward jet and two recirculation gyres are formed in the statistically steady state. The variability of velocity away from the recirculation gyres is as strong as that near the jet at deeper depths, and the structure of this velocity variability was analysed by using the technique of Frequency-Domain Empirical Orthogonal Functions (FDEOFs). Motions represented by the first FDEOFs consist of the barotropic Rossby waves of various periods, which are typically longer than a few dozen days. Although wavenumbers of the radiated Rossby waves change with their frequency and the magnitude of the inflow, U, and the planetary beta effect, , the wavenumbers scaled with k = √/U tend to be located on a single circle centered at the origin in the wavenumber domain. On this circle, the non-dimensional zonal phase speed of the Rossby waves is constant and is approximately equal to the non-dimensional maximum speed of recirculations. Wavenumber vectors, which are oriented in the southwest (northwest) direction on the northern (southern) side of the jets, tend to be more zonal at higher frequencies due to this constraint of the phase speed. There is an upper limit for the frequency of the Rossby waves that can attain this constant phase speed. At frequencies above this limit radiation of the barotropic Rossby waves is not clear. At frequencies lower than this limit motions represented by the first FDEOFs tend to extract energy from the mean circulation, and contribute to the eddy potential-vorticity flux, which tends to accelerate the mean circulation.
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Document Type: Research Article
Publication date: March 1, 2009
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