The linear theory of double diffusive interleaving is extended to take account of baroclinic effects. This study goes beyond previous studies by including the possibility of modes with nonzero tilt in the alongfront direction, which allows for advection by the baroclinic frontal flow. This requires that the stability equations be...
Mixing due to sheared salt fingers is studied by means of direct numerical simulations (DNS) of a double-diffusively unstable shear layer. The focus is on the “moderate shear” case, where shear is strong enough to produce Kelvin–Helmholtz (KH) instability but not strong enough to produce the subharmonic pairing instability. This...
Interleaving motions on a wide, baroclinic front are modeled using a second-moment closure to represent unresolved fluxes by turbulence and salt fingering. A linear perturbation analysis reveals two broad classes of unstable modes. First are scale-selective modes comparable with interleaving as observed in oceanic fronts. These correspond well with observations...
Motivated by the tendency of high-Prandtl-number fluids to form sharp density interfaces, the authors investigate the evolution of Holmboe waves in a stratified shear flow through direct numerical simulation. Like their better-known cousins, Kelvin–Helmholtz waves, Holmboe waves lead the flow to a turbulent state in which rapid irreversible mixing takes...
Deep cycle mixing in the cold tongue of the equatorial
Pacific Ocean is associated with a mean flow regime
in which the gradient Richardson number Ri (a ratio of
stratification to shear that affects the evolution of turbulence)
fluctuates about a critical value near 1/4. This is the state
of...
Full Text:
equatorial
Pacific Ocean
Smyth, W. D., and J. N. Moum (2013), Marginal instability and deep cycle
Deep cycle mixing in the cold tongue of the equatorial
Pacific Ocean is associated with a mean flow regime
in which the gradient Richardson number Ri (a ratio of
stratification to shear that affects the evolution of turbulence)
fluctuates about a critical value near 1/4. This is the state
of...
Deep cycle mixing in the cold tongue of the equatorial
Pacific Ocean is associated with a mean flow regime
in which the gradient Richardson number Ri (a ratio of
stratification to shear that affects the evolution of turbulence)
fluctuates about a critical value near 1/4. This is the state
of...
Direct numerical simulations are used to compare turbulent diffusivities of heat and salt during the growth and collapse of Kelvin–Helmholtz billows. The ratio of diffusivities is obtained as a function of buoyancy Reynolds number Re[subscript]b and of the density ratio R[subscript]ρ (the ratio of the contributions of heat and salt...
The time evolution of mixing in turbulent overturns is investigated using a combination of direct numerical simulations (DNS) and microstructure profiles obtained during two field experiments. The focus is on the flux coefficient Γ, the ratio of the turbulent buoyancy flux to the turbulent kinetic energy dissipation rate ϵ. In...
Narrowband oscillations observed in the upper equatorial Pacific are interpreted in terms of a random ensemble of shear instability events. Linear perturbation analysis is applied to hourly averaged profiles of velocity and density over a 54-day interval, yielding a total of 337 unstable modes. Composite profiles of mean states and...