| Summary: | A numerical model simulation investigates the influence of the mid-Atlantic ridge on non-linear barotropic and first-mode baroclinic Rossby waves generated by seasonal wind fluctuations. The north Atlantic is simulated by a square-box, two-layer quasi-geostrophic model. The bottom topography is ridge-like and compromises the QG approximation and the actual shape of the ridge. Sponge layers protect all boundaries except the eastern one from wave reflexion. The model is forced by a purely fluctuating wind stress curl derived from the most significant EOF's 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. Their frequencies range from 0.01 to 0.05 cpd. 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 cm sec('-1) propagate energy westward at 3 cm sec('-1). 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 wavetrains whose phase vector is almost normal to the ridge crest. Those waves propagate energy mostly westward at 2.9 cm sec('-1). The northern waves are out of phase with the southern ones because of the structure of the dominant wind pattern over the ridge region where they are generated. All waves have a small group velocity component in the meridional direction. It is northward (at 0.34 cm sec('-1)) for the northern waves and southward (at 0.32 cm sec('-1)) for the southern waves. Source: ...
|
|---|