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- Title
Diurnal Coastal Trapped Waves and Associated Deep‐Ocean Mixing Near the Head of Suruga Trough.
- Authors
Nagai, Taira; Hibiya, Toshiyuki
- Abstract
Coastal submarine canyons are expected to be sites of enhanced turbulent mixing which create productive fishing areas in coastal waters. Recent studies suggested the potential role of diurnal coastal trapped waves (CTWs) in inducing significant turbulent mixing in coastal submarine canyons poleward of 30° where the diurnal tide becomes subinertial. Nevertheless, the detailed physical processes responsible for the generation and dissipation of CTWs in such submarine canyons have hardly been investigated so far. In the present study, to investigate the turbulent mixing processes associated with diurnal CTWs in submarine canyons, we carry out high‐resolution (Δx, Δy = 1/240°) non‐hydrostatic three‐dimensional numerical experiments focusing on Suruga Bay located at the north end of Suruga Trough, Japan. The numerical experiments show that diurnal (subinertial) tidal currents over the Izu Ridge generate CTWs which propagate cyclonically along the coast of Suruga Bay. In the middle of Suruga Bay, bottom‐intensified flow due to the diurnal CTWs interacts with rough seafloor topography to excite upward propagating internal lee waves, which create mixing hotspots extending high above the seafloor. The resulting diurnal (subinertial) tidal energy dissipation in Suruga Bay is found to be much larger than that associated with semidiurnal (superinertial) internal tides. Furthermore, it is found that baroclinic energy flux based on a simple barotropic‐baroclinic decomposition severely underestimates the wave energy flux in areas with high CTW activity. These results strongly indicate that the existence of CTWs might be a key factor to clarify the dissipation/mixing processes in submarine canyons. Plain Language Summary: Recent microstructure measurements indicate that strong turbulent mixing in submarine canyons causes the increase of biological productivity through upwelling of deep water. In the present study, we numerically investigate the mixing processes in submarine canyons. It is found that, in Suruga Bay located at the north end of Suruga Trough, Japan, coastal trapped waves (CTWs) propagating cyclonically along the coast of Suruga Bay interact with rough seafloor topography to excite small‐scale internal waves that break inducing significant mixing. These results suggest that numerical models that resolve small‐scale rough seafloor topography are indispensable to numerically investigate the turbulent mixing processes in submarine canyons. Key Points: The mixing processes associated with diurnal coastal trapped waves (CTWs) in Suruga Bay are investigated through numerical experimentsDiurnal CTWs propagating into Suruga Bay interact with small‐scale topography to excite internal lee waves that produce mixing hotspotsAnalyses based on a barotropic‐baroclinic decomposition may cause a large error in estimating energy flux in areas with high CTW activity
- Subjects
SUBMARINE valleys; SUBMARINE topography; INTERNAL waves; TURBULENT mixing; MOUNTAIN wave; WINDSTORMS; GEOLOGIC hot spots
- Publication
Journal of Geophysical Research. Oceans, 2022, Vol 127, Issue 7, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2022JC018457