Long extra-tropical planetary wave propagation in the presence of slowly varying mean flow and bottom topography. I: the local problem
نویسندگان
چکیده
One of the most successful theories to date to explain why observed planetary waves propagate westwards faster than linear flat-bottom theory predicts has been to include the effect of background baroclinic mean flow, which modifies the potential vorticity waveguide in which the waves propagate. (Barotropic flows are almost everywhere too small to explain the observed differences.) That theory accounted for most, but not all, of the observed wave speeds. A later attempt to examine the effect of the sloping bottom on these waves (without the mean flow effect) did not find any overall speed-up. This paper combines these two effects, assuming long (geostrophic) waves and slowly varying mean flow and topography, and computes group velocities at each point in the global ocean. These velocities turn out to be largely independent of the orientation of the wavevector. A second speed-up of the waves is found (over that for mean flow only). Almost no eastward-oriented group velocities are found, so that features which appear to propagate in the same sense as a subtropical gyre would have to be coupled with the atmosphere or be density-compensated in some manner.
منابع مشابه
Long Extratropical Planetary Wave Propagation in the Presence of Slowly Varying Mean Flow and Bottom Topography. Part II: Ray Propagation and Comparison with Observations
Ray theory is used to predict phase and group velocities for long planetary waves under realistic, albeit slowly varying, oceanic conditions. The results are compared with local theory using fields smoothed to the same amount (98 latitude/longitude) as well as those with much less smoothing (18). The agreement is excellent, showing that local theory forms a good proxy for ray theory results. Th...
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1926 JOURNAL OF PHYSICAL OCEANOGRAPHY VOLUME 31 Reply
Hallberg (1997) used a combination of quasigeostrophic ray tracing and primitive equation numerical simulations to study the propagation of topographic and planetary Rossby waves around an ocean basin with slowly varying but arbitrary topography. When the topographic and planetary vorticity gradients are not parallel to each other, the classical baroclinic and barotropic modes are replaced by m...
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