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It is generally understood that the origin of ocean diapycnal diffusivity is primarily associated with the stratified turbulence produced by breaking internal (gravity) waves (IW). However, it requires significant effort to verify diffusivity values in ocean general circulation models in any particular geographical region of the ocean due to the scarcity of microstructure measurements. Recent analyses of downscaled IW fields from an internal‐wave‐admitting global ocean simulation into higher‐resolution regional configurations northwest of Hawaii have demonstrated a much‐improved fit of the simulated IW spectra to the in‐situ profiler measurements such as the Garrett‐Munk (GM) spectrum. Here, we employ this dynamically downscaled ocean simulation to directly analyze the nature of the IW‐breaking and the wave‐turbulence cascade in this region. We employ a modified version of the Kappa Profile Parameterization (KPP) to infer what the horizontally averaged vertical profile of diapycnal diffusivity should be, and compare this to the background profile that would be employed in the ocean component of a low‐resolution coupled climate model such as the Community Earth System Model (CESM) of the US National Center for Atmospheric Research (NCAR). In pursuing this goal, we also demonstrate that the wavefield in the high‐resolution regional domain is dominated by a well‐resolved spectrum of low‐mode IWs that are predictable by solving an appropriate eigenvalue problem for stratified flow. We finally suggest a new tentative approach to improve the KPP parameterization. Plain Language Summary: A much‐improved spectrum of the simulated internal wave (IW) field has recently been obtained by downscaling a global ocean model into a higher‐resolution regional configuration. The global simulation is based on the Massachusetts Institute of Technology general circulation model (MITgcm) forced by both astronomical tidal potential and surface atmospheric processes. By employing a mathematical framework to predict the structure of IWs, we first demonstrate that the interior wavefield of the high‐resolution regional domain is well dominated by a series of low‐order IW modes. Then, we address the issue as to whether the component of the K‐Profile Parameterization (KPP) associated with IW shear might be able to explain the physical origins of the background depth dependence of diapycnal diffusivity that would normally be employed in the ocean component of a modern coupled climate model. Finally, we suggest a tentative approach to further improve KPP. Key Points: A representation of internal wave modes that includes dissipation is derived that explains spectra in a tidally forced numerical simulationEliminating the background component of KPP leads to a representation of the physics of internal wave breakingRealistic diapycnal diffusivity profiles can be obtained by minor adjustments to the shear component of KPP [ABSTRACT FROM AUTHOR]

Observations are reported of the semidiurnal ( M2) internal tide across Kaena Ridge, Hawaii. Horizontal velocity in the upper 1000-1500 m was measured during eleven ~240-km-long shipboard acoustic Doppler current profiler (ADCP) transects across the ridge, made over the course of several months. The M2 motions are isolated by means of harmonic analysis and compared to numerical simulations using the Princeton Ocean Model (POM). The depth coverage of the measurements is about 3 times greater than similar past studies, offering a substantially richer view of the internal tide beams. Sloping features are seen extending upward north and south from the ridge and then downward from the surface reflection about ±40 km from the ridge crest, closely matching theoretical M2 ray paths and the model predictions. [ABSTRACT FROM AUTHOR]

The northeastward progression of the semidiurnal internal tide from French Frigate Shoals (FFS), Hawaii, is studied with an array of six simultaneous profiling moorings spanning 25.5°–37.1°N (≈1400 km) and 13-yr-long Ocean Topography Experiment (TOPEX)/Poseidon (T/P) altimeter data processed by a new technique. The moorings have excellent temporal and vertical resolutions, while the altimeter offers broad spatial coverage of the surface manifestation of the internal tide’s coherent portion. Together these two approaches provide a unique view of the internal tide’s long-range propagation in a complex ocean environment. The moored observations reveal a rich, time-variable, and multimodal internal tide field, with higher-mode motions contributing significantly to velocity, displacement, and energy. In spite of these contributions, the coherent mode-1 internal tide dominates the northeastward energy flux, and is detectable in both moored and altimetric data over the entire array. Phase and group propagation measured independently from moorings and altimetry agree well with theoretical values. Sea surface height anomalies (SSHAs) measured from moorings and altimetry agree well in amplitude and phase until the northern end of the array, where phase differences arise presumably from refraction by mesoscale flows. Observed variations in SSHA, energy flux, and kinetic-to-potential energy ratio indicate an interference pattern resulting from superposed northeastward radiation from Hawaii and southeastward from the Aleutian Ridge. A simple model of two plane waves explains most of these features. [ABSTRACT FROM AUTHOR]

Large semidiurnal vertical displacements (≈100 m) and strong baroclinic currents (≈0.5 m s-1; several times as large as barotropic currents) dominate motions in Mamala Bay, outside the mouth of Pearl Harbor, Hawaii. During September 2002, the authors sought to characterize them with a 2-month McLane moored profiler deployment and a 4-day intensive survey with a towed CTD/ADCP and the Research Vessel (R/V) Revelle hydrographic sonar. Spatial maps and time series of turbulent dissipation rate ε, diapycnal diffusivity Kρ, isopycnal displacement η, velocity u, energy E, and energy flux F are presented. Dissipation rate peaks in the lower 150 m during rising isopycnals and high strain and shows a factor-of-50 spring–neap modulation. The largest Kρ values, in the western bay near a submarine ridge, exceed 10-3 m2 s-1. The M2 phases of η and u increase toward the west, implying a westward phase velocity cp ≈ 1 m s-1 and horizontal wavelength ≈60 km, consistent with theoretical mode-1 values. These phases vary strongly (≈±45°) in time relative to astronomical forcing, implying remotely generated signals. Energy and energy flux peak 1–3 days after spring tide, supporting this interpretation. The group velocity, computed as the ratio F/E, is near ≈1 m s-1, also in agreement with theoretical mode-1 values. Spatial maps of energy flux agree well with results from the Princeton Ocean Model, indicating converging fluxes in the western bay from waves generated to the east and west. The observations indicate a time-varying interference pattern between these waves that is modulated by background stratification between their sources and Mamala Bay. [ABSTRACT FROM AUTHOR]