Rossby Waves in the Tropical North Pacific and Their Role in Decadal Thermocline Variability

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Abstract
A band of enhanced thermocline variability at 10°–15°N in the Pacific found in nature also occurs in an ocean general circulation model forced with observed fluxes of momentum, heat, and freshwater over the period 1958–97. The variability in the model is primarily associated with long baroclinic Rossby waves characterized by periods in the decadal range (7–10 yr). The waves are forced by westward propagating Ekman pumping anomalies east of the date line and propagate at a speed of ∼13 cm s−1, which is slower than the phase speed of the first mode unforced baroclinic waves (15–16 cm s−1). West of the date line, the correlations between thermocline displacements and local Ekman pumping are relatively small, and the ocean signals have a phase speed of ∼20 cm s−1, very similar to the phase speed of the first baroclinic mode in the western half of the basin (18–20 cm s−1). The phase speeds of the ocean model signals have been estimated using cospectral analysis, while the WKB approximation has been us... Abstract A band of enhanced thermocline variability at 10°–15°N in the Pacific found in nature also occurs in an ocean general circulation model forced with observed fluxes of momentum, heat, and freshwater over the period 1958–97. The variability in the model is primarily associated with long baroclinic Rossby waves characterized by periods in the decadal range (7–10 yr). The waves are forced by westward propagating Ekman pumping anomalies east of the date line and propagate at a speed of ∼13 cm s−1, which is slower than the phase speed of the first mode unforced baroclinic waves (15–16 cm s−1). West of the date line, the correlations between thermocline displacements and local Ekman pumping are relatively small, and the ocean signals have a phase speed of ∼20 cm s−1, very similar to the phase speed of the first baroclinic mode in the western half of the basin (18–20 cm s−1). The phase speeds of the ocean model signals have been estimated using cospectral analysis, while the WKB approximation has been us...