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- Title
Momentum Flux Convergence From Internal Tides in the North Equatorial Countercurrent Upstream of a Submarine Ridge Near Merir Island, Palau.
- Authors
Johnston, T. M. Shaun; Ou, Celia Y.
- Abstract
In the presence of a mean flow, theory and models for internal tide generation at smallamplitude topography show (a) internal tides produce a net momentum flux that extends to the surface and (b) fluxes are directed preferentially upstream. Here, we observe internal tides propagating into the North Equatorial Countercurrent during two spatial surveys near a submarine ridge. On the second survey during a diurnal spring tide, we note elevated shear upstream of the ridge below 112 m with corresponding low Richardson numbers, which suggests the internal waves are dissipating due to shear instability. Reduced amplitudes are noted above 150 m. Internal tidal motions were isolated by performing a phase average over a wavelength upstream of the topography. Momentum flux convergence and divergence are noted upstream of the ridge, have a similar magnitude to mean flow acceleration terms, and are about 10% of the largest mean flow terms. The internal tides were noted upstream and appeared weaker downstream, but due to the topographic wake similar calculations could not be performed downstream. Tall, steep topography and strong equatorial currents are found throughout the lowlatitude western Pacific, which suggests such infrequently observed internal tide flux divergences may be commonly contributing to the momentum of mean flows. Plain Language Summary Internal tides are produced as surface tides move stratified water over submarine ridges. In a mean flow, the waves' energy and momentum are directed preferentially upstream according to theory and models. Here, we observe internal tides propagating into a strong equatorial current during two spatial surveys. During the second survey, we note elevated current shear upstream of the ridge. This result suggests the internal tides are dissipating and depositing their momentum upstream of their generation site, which affects the mean current there at the 10% level. Tall, steep topography and strong equatorial flows are found throughout the western Pacific, which suggests this infrequently observed process may be affecting mean currents there.
- Subjects
HEAT flux; TIDES; COUNTERCURRENT processes; COUNTER-flow heat exchangers; WAVELENGTHS
- Publication
Journal of Geophysical Research. Oceans, 2021, Vol 126, Issue 2, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2020JC016770