Abstract
To assess each of the two possible mechanisms responsible for the fortnightly modulation of semi-enclosed basin–ocean water exchange (‘density tides’), a set of numerical experiments is carried out using a vertically two-dimensional numerical model with realistic situations in Puget Sound in mind. It is found that, although the localized vertical viscosity (or the localized vertical diffusivity) enhanced in the entrance sill region primarily controls the bottom-water transport (or the bottom-water density) during spring tides, it does not lead to any appreciable variations of bottom-water density (or bottom-water transport). This indicates that the fortnightly modulation of vertical viscosity and that of vertical diffusivity both play important roles in creating density tides. In the real ocean, the vertical viscosity and diffusivity are enhanced simultaneously during spring tides, so that it is difficult to discriminate between both effects on density tides. This causes the widespread misunderstanding that density tides are mainly caused by the decreased advection of dense bottom-water from outside due to the enhanced vertical viscosity during spring tides.
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de Silva Samarasinghe JR, Lennon GW (1987) Hypersalinity, flushing and transient salt-wedges in a tidal gulf-an inverse estuary. Estuar Coast Shelf Sci 24:483–498
Farmer DM, Smith JD (1980) Tidal interaction of stratified flow with a sill in Knight Inlet. Deep Sea Res 27A:239–254
Geyer WR, Cannon GA (1982) Sill processes related to deep water renewal in a fjord. J Geophys Res 87:7985–7996
Griffin DA, LeBlond PH (1990) Estuary/ocean exchange controlled by spring-neap tidal mixing. Estuar Coast Shelf Sci 30:275–297
Hibiya T (1986) Generation mechanism of internal waves by tidal flow over a sill. J Geophys Res 91:7697–7708
Hibiya T, LeBlond PH (1993) The control of fjord circulation by fortnightly modulation of tidal mixing processes. J Phys Oceanogr 23:2042–2052
Hibiya T, Ogasawara M, Niwa Y (1998) A numerical study of the fortnightly modulation of basin–ocean water exchange across a tidal mixing zone. J Phys Oceanogr 28:1224–1235
LeBlond PH, Ma H, Doherty F, Pond S (1991) Deep and intermediate water replacement in the Strait of Georgia. Atmos Ocean 29:288–312
Marshall J, Adcroft A, Hill C, Perelman L, Heisey C (1997) A finite-volume, incompressible Navier Stokes model for studies of the ocean on parallel computers. J Geophys Res 102:5753–5766
Maxworthy T (1979) A note on the internal solitary waves produced by tidal flow over a three-dimensional ridge. J Geophys Res 84:338–346
Maxworthy T (1980) On the formation of nonlinear internal waves from the gravitational collapse of mixed regions in two and three dimensions. J Fluid Mech 96:47–64
Nunes RA, Lennon GW (1987) Episodic stratification and gravity currents in a marine environment of modulated turbulence. J Geophys Res 92:5465–5480
Valle-Levinson A, Jara F, Molinet C, Soto D (2001) Observations of intratidal variability of flows over a sill/contraction combination in a Chilean fjord. J Geophys Res 106:7051–7064
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Nagai, T., Hibiya, T. The processes of semi-enclosed basin–ocean water exchange across a tidal mixing zone. J Oceanogr 67, 533–539 (2011). https://doi.org/10.1007/s10872-011-0045-0
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DOI: https://doi.org/10.1007/s10872-011-0045-0