[A-OS14] Coastal physical processes associated with mixing, eddies, internal waves

[AOS14-03] Numerical study of tide-induced deep-ocean mixing near the head of Suruga Trough

*Taira Nagai¹, Toshiyuki Hibiya¹ (1.Graduate School of Science, The University of Tokyo)

Keywords:Suruga Trough, Internal tides, Coastal trapped waves

Coastal submarine canyons are widely expected to be sites of enhanced mixing which may offer a potential solution to the ‘missing mixing’ problem. In Suruga Bay, mooring observations along the steep submarine canyon (Suruga Trough) show the existence of strong semi-diurnal and diurnal internal tides near the ocean bottom. In this trough, therefore, enhanced turbulent mixing induced by breaking of these internal tides is expected, although details of physical processes that produce strong internal tides have not been discussed yet.

In order to investigate the excitation processes of internal tides in Suruga Trough, we carry out a couple of high-resolution (Δx, Δy = 1/240^o) non-hydrostatic three-dimensional numerical experiments incorporating realistic semi-diurnal (M₂) and diurnal (K₁) tidal forcing, respectively. We first investigate the energetics of M₂ internal-tide to show that (1) internal tides generated over Izu Ridge propagate towards Suruga Trough, (2) in which the incident waves interact with the reflected waves from the trough head, and finally (3) the internal tide energy together with its dissipation is intensified. The K₁ tidal frequency, on the other hand, is subinertial in this area, so that K₁ tidal flow mainly generates coastal trapped waves which propagate cyclonically along the coast of Suruga Bay. It is suggested that these coastal trapped waves induce strong velocity shear near the bottom of the trough causing bottom confined intense mixing.