A conceptual framework for analysing the energetics of density-stratified Boussinesq fluid flows is discussed. The concept gravitational available potential energy used to formulate an budget in which evolution background energy, i.e. minimum attainable through adiabatic motions, can be explicitly examined. For closed systems, change only due diabatic processes. rate proportional molecular diffusivity. Changes provide a direct measure changes irreversible diapycnal mixing. open also boundary...

Many nearshore fish and invertebrate populations are overexploited even when apparently coherent management structures in place. One potential cause of mismanagement may be a poor understanding accounting stochasticity, particularly for stock recruitment. the fishes invertebrates that comprise fisheries relatively sedentary as adults but have an obligate larval pelagic stage is dispersed by ocean currents. Here, we demonstrate connectivity inherently intermittent heterogeneous process on...

Basin—scale internal waves provide the driving forces for vertical and horizontal fluxes in a stratified lake below wind‐mixed layer. Thus, correct modeling of mixing transport requires accurate basin‐scale waves: examining this capability with hydrostatic, z‐coordinate three‐dimensional (3D) numerical model at coarse grid resolutions is focus paper. It demonstrated that capturing thermocline forcing 3D mixed‐layer surface dynamics results good representation low‐frequency wave dynamics. The...

An idealized numerical study of a northward propagating internal tide reveals dramatic loss energy to small‐scale subharmonic instabilities near 28.9°N. Inspired by observations the radiating from Hawaiian Ridge, three‐dimensional model is initialized with baroclinic tidal flux approximately 1.7 kW/m. After an initial spinup period, quickly transferred motions, half horizontal wavenumber and small vertical scales, through nonlinear advection velocity gradients. Potential oceanic implications...

Abstract The effects of internal waves (IWs), externally forced by high-frequency wind, on energy pathways are studied in submesoscale-resolving numerical simulations an idealized wind-driven channel flow. Two processes examined: the direct extraction mesoscale IWs followed IW forward cascade to dissipation and stimulated imbalance, a mechanism through which trigger submesoscale dissipation. This study finds that frequency wavenumber spectral slopes shallower solutions with forcing compared...

We define the rate at which a scalar θ mixes in fluid flow terms of flux across isoscalar surfaces. This d is purely diffusive and is, principle, exactly known all times given field coefficient molecular diffusivity. In general, complex geometry surfaces would appear to make calculation this very difficult. paper, we derive an exact expression relating instantaneous diascalar average squared gradient on surface does not require knowledge spatial structure itself. To obtain result,...

The behaviour of internal gravity wave packets approaching a critical level is investigated through numerical simulation. Initial-value problems are formulated for both small- and large-amplitude packets. Wave propagation the early stages interaction with mean shear two-dimensional result in trapping energy near level. subsequent dynamics instability, however, fundamentally different two- three-dimensional calculations. Three-dimensionality develops by transverse convective instability wave....

Linearly stratified salt solutions of different Prandtl number were subjected to turbulent stirring by a horizontally oscillating vertical grid in closed laboratory system. The experimental set-up allowed the independent direct measurement root mean square lengthscale L t , diffusivity for mass K ρ rate dissipation kinetic energy ε, buoyancy frequency N and viscosity v as time volume averaged quantities. behaviour both was characterized over wide range turbulence intensity measure, ε/ vN 2...

Motivated by the tendency of high-Prandtl-number fluids to form sharp density interfaces, authors investigate evolution Holmboe waves in a stratified shear flow through direct numerical simulation. Like their better-known cousins, Kelvin–Helmholtz waves, lead turbulent state which rapid irreversible mixing takes place. In both cases, significant also place prior transition turbulence. Although grow more slowly than net amount is comparable. It concluded that instability represents...

Abstract A tidally driven, stratified boundary layer over supercritical topography is simulated numerically. The near‐boundary flow characterized by quasiperiodic, bore‐like motions and episodic expulsion events where fluid ejected into the interior. character of bores compared to high‐resolution ocean mooring data van Haren (2006). diffusivity near estimated means a synthetic dye tracer experiment. average dissipation rate within cloud computed combined with estimate yield an overall mixing...

Abstract In ice‐covered lakes, penetrative radiation warms fluid beneath a diffusive boundary layer, thereby increasing its density and providing energy for convection in diurnally active, deepening mixed layer. Shallow regions are differentially heated to warmer temperatures, driving turbulent gravity currents that transport warm water downslope into the basin interior. We examine energetics of these processes, focusing on rate at which supplies is available drive motion. Using numerical...

Abstract Although typically used to measure dynamic strain from seismic and acoustic waves, Rayleigh‐based distributed sensing (DAS) is also sensitive temperature, offering longer range higher sensitivity small temperature perturbations than conventional Raman‐based sensing. Here, we demonstrate that ocean‐bottom DAS can be employed study internal wave tide dynamics in the bottom boundary layer, a region of enhanced ocean mixing but scarce observations. First, show transients up about 4 K...

Numerical simulations of bidirectional density‐driven exchange flows are used to study the effects turbulent mixing in these flows. The numerical experiments designed so that it is possible specify intensity mixing, which allows investigation a wide range difficult model laboratory. simulated compared two analytical solutions, first, two‐layer hydraulic solution has no and second, dominates flow. We able similar either limits by modifying as well simulating behavior between extremes....

We analyse the low-mode structure of internal tides generated in laboratory experiments and numerical simulations by a two-dimensional ridge channel finite depth. The height is approximately half depth regimes considered span sub- to supercritical topography. For small tidal excursions, order 1% topographic width, our results agree well with linear theory. larger up 15% we find that scaled mode 1 conversion rate decreases less than 15%, spite nonlinear phenomena break down familiar wave-beam...

Abstract A large fraction of the kinetic energy in ocean is stored “quasigeostrophic” eddy field. This “balanced” field expected, according to geostrophic turbulence theory, transfer larger scales. In order for general circulation remain approximately steady, instability mechanisms leading loss balance (LOB) have been hypothesized take place so that (EKE) may be transferred small scales where it can dissipated. study examines pathways fully resolved direct numerical simulations flow a...

A laboratory study was carried out to directly measure the turbulence properties in a benthic boundary layer (BBL) above uniformly sloping bottom where BBL is energized by internal waves. The ambient fluid continuously stratified and steadily forced incoming wave field consisted of confined beam, restricting turbulent activity finite region along slope. Measurements dissipation showed some variation over phase, but cycle-averaged values indicated that nearly constant with height within BBL....

We investigate the transport of mass and momentum between layers in idealized exchange flow through a contracting channel. Lock-exchange initial value problems are run to approximately steady state using three-dimensional, non-hydrostatic numerical model. The model resolves large-scale shear instabilities that form at interface, parameterizing effects subgrid-scale turbulence. closure scheme is based on an assumed steady, local balance turbulent production dissipation density-stratified...

A numerical model designed for three-dimensional process studies of rotating, stratified flows is described. The freely available, parallel, and portable across a range computer architectures. underlying numerics are high quality, based on spectral expansions, third-order time stepping. Optional submodels include accurate calculation Lagrangian trajectories. Special consideration has been taken to ensure ease use by geophysical, as distinguished from computational, scientists. mathematical...

We consider the mechanical energy budget for horizontal Boussinesq convection and show that there are two distinct pathways connecting (i.e. kinetic, available potential background energies) to internal reservoir external source. To obtain bounds on magnitudes of transfer rates around each cycle, we first volume-averaged dissipation rate buoyancy variance χ ≡ κ 〈|∇ b | 2 〉, where is buoyancy, bounded from above by 4.57 h −1 2/3 ν −1/3 7/3 max . Here depth container, molecular diffusion,...

Abstract The dynamics of a forced, low-mode oceanic internal tide propagating poleward on β plane are investigated numerically. focus is the transfer energy from to near-inertial oscillations (NIOs) initiated by weakly nonlinear interaction known as parametric subharmonic instability (PSI). It shown that PSI mechanism for generating NIOs in upper ocean, which subsequently radiate depth. exponentially growing eventually reach finite amplitude, and further with leads quasi-steady state...

Abstract ‘Horizontal convection’ (HC) is the generic name for flow resulting from a buoyancy variation imposed along horizontal boundary of fluid. We study effects rotation on three-dimensional HC numerically in two stages: first, when baroclinic instability suppressed and, second, it ensues and eddies are formed. concentrate changes to thickness near-surface layer, stratification at depth, overturning circulation energetics during each these stages. Our results show that, moderate flux...

Turbulent oscillatory flow over sand ripples is examined using three‐dimensional numerical simulations. The model solves the time‐dependent Navier‐Stokes equations on a curvilinear grid in horizontally periodic domain. transitions to turbulence and presence of increases rate dissipation shoaling wave energy compared smooth boundary. influence ripple shape shown alter mean field affect induced drag rates. Shear instabilities near boundary during phases reversal resulting vortex shedding from...

A high‐resolution two‐dimensional numerical model is used to simulate the propagation of finite amplitude internal wave packets into a mean shear flow that varies slowly in space. For moderate packet amplitudes interaction well described by weakly nonlinear asymptotic theory. At higher amplitude, however, region develops near critical level which nonlinearity dominates, becomes unstable, and wavelike motion breaks down smaller scales. The form observed breakdown unexpected convectively...