North pacific internal tides from the Aleutian Ridge: Altimeter observations and modeling

Internal tides radiating into the North Pacific from the Aleutian Ridge near Amukta Pass are examined using 7 years of Topex/Poseidon altimeter data. The observations show coherent southward phase propagation at the M-2 frequency over a distance of at least 1100 km into the central Pacific. Barotropic and baroclinic models are applied to study this internal tidal signal. Results from the barotropic model show that the strongest cross-slope volume and energy fluxes occur in the vicinity of Amukta Pass, helping to establish this region as an important site for baroclinic energy conversion along the eastern half of the ridge. A two-dimensional version of the Princeton Ocean Model is used to simulate internal tide generation and propagation. A comparison between the altimeter data south of the ridge and the sea-surface signature of the internal tide signal of the model shows good agreement for the phase, both close to the source and well into the far field. Comparison of the phase between model and data also provides evidence for wave refraction. This occurs due to the slow modulation of wavelength associated with the variation in the Coriolis parameter encountered as the internal tide propagates southward. The model results suggest that the net rate of conversion of barotropic to baroclinic energy is about 1.8 GW in the vicinity of Amukta Pass. This represents about 6% of the local barotropic energy flux across the ridge and perhaps 1% of global baroclinic conversion.