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A Numerical Study on the Influence of the Mid-Atlantic Ridge on Nonlinear Barotropic and First-Mode Baroclinic Rossby Waves Generated by Seasonal Winds.
FLORIDA STATE UNIV TALLAHASSEE MESOSCALE AIR-SEA INTERACTION GROUP
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A numerical model simulation investigates the influence of the mid-Atlantic ridge on nonlinear barotropic and first-mode baroclinic Rossby waves generated by seasonal wind fluctuations. The north Atlantic is simulated by a square-box, two-layered quasigeostrophic model. The bottom topography is ridgelike and compromises the QG approximation and the actual shape of the ridge. Sponge layers protect all boundaries except the eastern one from wave reflection. The model is forced by a purely fluctuating wind stress curl derived from the most significant EOFs of the FGGE winds. A flat bottom and a ridge experiment are compared. The topography is an important source of barotropic variability for the eastern basin. The topographic Rossby waves generated over the ridge, either by wave reflexion or by direct wind forcing, account for at least 50 of the barotropic variability of that basin. In both experiments the eastern boundary is an important source of annual-period baroclinic Rossby waves. Wavetrains having a wavelength of about 1060 km and a westward phase speed around 3.4 cmsec propagate energy westward at 3cmsec. In the flat bottom experiment a source of directly wind forced baroclinic waves of annual period is found in the middle of the basin. Their amplitude is smaller and they have a noticeable northward phase propagation resulting in a southward group velocity component. The topography blocks the waves coming from the eastern boundary but generates new wave trains whose phase vector is almost normal to the ridge crest.
APPROVED FOR PUBLIC RELEASE