The authors thank Eric Slater, Mike Goldin, Lloyd Green, Tony Aja, and Tyler Hughen for the design, construction, and operation of the instruments used in this experiment. Prof. Tom Peacock provided the Echeverri and Peacock (2010) model and Dr. Shaun Johnston graciously provided POM output for the FLIP site. Captain Tom Golfinos and the crew of the R/P FLIP ably deployed the trimooring on the edge of Kaena Ridge crest and operated the platform for the duration of the experiment. This work was supported by NSF as an aspect of the Hawaii Ocean Mixing Experiment.
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Using a buoyancy-driven profiling instrument, Jacobs and Cox (1987), Duda and Cox (1989), and Duda and Jacobs (1998) have detected small but statistically significant stress associated with the propagation of short, high-frequency waves in a background inertial shear. van Haren et al. (1994) have detected wave stress in stratified water above the seafloor in the Strait of Juan del Fuca.
It is convenient to refer to the semidiurnal (D2) and diurnal (D1) tides generically and note their fortnightly cycles, rather than discuss individual tidal constituents, such as M2, S2, etc., which are imprecisely resolved in the present 35-day record.
The prefix “pseudo,” introduced to geoscience by McIntyre (1981) from classical mechanics, acknowledges the intellectual challenge of isolating the momentum of a wave from that of the medium through which it propagates.
The deep (>600 m) acoustic scattering cross section was much greater over Kaena Ridge than in the open ocean, enabling the good depth penetration of the sonar.
For temporally stationary processes, the cross-spectral approach is the accepted standard for flux estimation. However, when the background flow is periodic, time variability can cause high-frequency phenomena to “disappear” in cross-spectral flux descriptions. For example, small-scale topography on the ridge can be expected to trigger high-frequency lee waves. These might support a significant momentum flux, but direction of the flux will reverse with each reversal of the D2 current. Cross spectra that are estimated from records of duration sufficient to resolve the D2 momentum flux will blur the view of higher-frequency fluxes. Cross-spectral analysis does not distinguish between a large but reversing flux and a steady small flux.
On the upper ridge flanks, vertical displacements exceeding ±150 m are seen (Levine and Boyd 2006).
These signals would be easily detectable with Plueddemann’s 1983 technology.
In laterally homogeneous situations, it is often practical to define local coordinates such that 〈u3〉 = 0. However, applying the criterion 〈u3〉 = 0 in the presence of lee waves yields a spatially varying definition of “up.”
For a back-to-back sonar beam pair rotated by δ in the plane of the beams, errors in u1 and u2 are O(δ2) or smaller.
For broadband, quasi-linear wave fields, the triple products will also vanish.
This result depends on the fact that slope and velocity vary at the same frequency. A “frozen,” frontal slope, under lateral advection, leads to a fictitious vertical stress.
Although immune to fine structure contamination, the advective error