Propagation and Decay of Forced and Free Baroclinic Rossby Waves in Off-Equatorial Oceans

Abstract

Baroclinic Rossby wave motions in the off-equatorial oceans are investigated with emphasis on how eddy dissipation can influence the propagation of the height anomalies when both the forced wave response to wind in the interior ocean and the free wave response originating along the ocean?s coastal and topographic boundaries are present. By explicitly estimating the decay scale for the long baroclinic Rossby wave, the authors show that the forced wave patterns at all off-equatorial regions appear to propagate westward at 2cr, where cr is the phase speed of the long baroclinic wave. The presence of the boundary-generated, free Rossby waves in the low latitudes, however, reinforces the 1cr phase propagation in the combined height anomaly fields. Toward higher latitudes, this reinforcement weakens as the boundary-generated, free waves become highly dissipative; as a result, the forced wave motion becomes more dominant, which works to increase the apparent phase speed up to 2cr. In the subpolar regions where the annual baroclinic Rossby waves become evanescent, an apparent phase speed higher than 2cr is observed when an annual, standing wave response and a propagating wave response with an interannual frequency coexist. Stronger annual and interannual wind fluctuations over the Southern Hemisphere subpolar regions than over the Northern Hemisphere subpolar regions suggest that this coupling, and the phase speed higher than 2cr, are more likely to be detected in the Southern Hemisphere subpolar oceans.