Internal Tides and Turbulence along the 3000-m Isobath of the Hawaiian Ridge

Abstract

Full-depth velocity and density profiles taken along the 3000-m isobath characterize the semidiurnal internal tide and bottom-intensified turbulence along the Hawaiian Ridge. Observations reveal baroclinic energy fluxes of 21 ± 5 kW m?1 radiating from French Frigate Shoals, 17 ± 2.5 kW m?1 from Kauai Channel west of Oahu, and 13 ± 3.5 kW m?1 from west of Nihoa Island. Weaker fluxes of 1?4 ± 2 kW m?1 radiate from the region near Necker Island and east of Nihoa Island. Observed off-ridge energy fluxes generally agree to within a factor of 2 with those produced by a tidally forced numerical model. Average turbulent diapycnal diffusivity K is (0.5?1) ? 10?4 m2 s?1 above 2000 m, increasing exponentially to 20 ? 10?4 m2 s?1 near the bottom. Microstructure values agree well with those inferred from a finescale internal wave-based parameterization. A linear relationship between the vertically integrated energy flux and vertically integrated turbulent dissipation rate implies that dissipative length scales for the radiating internal tide exceed 1000 km.