The diffusive regime of double-diffusive convection

Kelley, Dan; Fernando, H. J. S.; Gargett, Ann E.; Tanny, Josef; Özsoy, Emi̇n

doi:10.1016/s0079-6611(03)00026-0

Cited by 169 publications

(199 citation statements)

References 130 publications

(192 reference statements)

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“…Schmitt 1994;Ruddick 1997;Kelley et al 2003) to adopt the one-component Phillips-Posmentier conceptualization to double-diffusive layering. The Phillips-Posmentier model captures only one aspect of the problem -the ρ z effect (figure 2a).…”

Section: ) Wherementioning

confidence: 99%

Applicability and failure of the flux-gradient laws in double-diffusive convection

Radko

2014

J. Fluid Mech.

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Double-diffusive flux-gradient laws are commonly used to describe the development of large-scale structures driven by salt fingers -thermohaline staircases, collective instability waves and intrusions. The flux-gradient model assumes that the vertical transport is uniquely determined by the local background temperature and salinity gradients. While flux-gradient laws adequately capture mixing characteristics on scales that greatly exceed those of primary double-diffusive instabilities, their accuracy rapidly deteriorates when the scale separation between primary and secondary instabilities is reduced. This study examines conditions for the breakdown of the flux-gradient laws using a combination of analytical arguments and direct numerical simulations. The applicability (failure) of the flux-gradient laws at large (small) scales is illustrated through the example of layering instability, which results in the spontaneous formation of thermohaline staircases from uniform temperature and salinity gradients. Our inquiry is focused on the properties of the 'point-of-failure' scale (H pof ) at which the vertical transport becomes significantly affected by the non-uniformity of the background stratification. It is hypothesized that H pof can control some key characteristics of secondary double-diffusive phenomena, such as the thickness of high-gradient interfaces in thermohaline staircases. A more general parametrization of the vertical transport -the flux-gradient-aberrancy lawis proposed, which includes the selective damping of relatively short wavelengths that are inadequately represented by the flux-gradient models. The new formulation is free from the unphysical behaviour of the flux-gradient laws at small scales (e.g. the ultraviolet catastrophe) and can be readily implemented in theoretical and large-scale numerical models of double-diffusive convection.

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Section: ) Wherementioning

confidence: 99%

Applicability and failure of the flux-gradient laws in double-diffusive convection

Radko

2014

J. Fluid Mech.

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“…Due to limited vertical resolution, it is unclear whether there are occurrences of split layers that appear to form and re-merge in hours, or whether the observations are indicating thickness changes in layers. Split layers are commonly observed in oceanographic profiles from other regions (Kelley et al, 2003). Kelley (1988) suggested that staircase layer thickness is controlled by layer splitting where new layers are formed from existing interfaces.…”

Section: A Sub-inertial Motion At Site D I Deep Water Columnmentioning

confidence: 99%

Moored observations of bottom-intensified motions in the deep Canada Basin, Arctic Ocean

Timmermans¹,

Rainville²,

Thomas³

et al. 2010

j mar res

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In the deep Canada Basin, below the sill depth (about 2400 m) of the Alpha-Mendeleyev Ridge, potential temperature and salinity first increase with depth, then remain uniform from about 2600 m to the bottom (approximately 3500 m). Year-long moored measurements of temperature, salinity and pressure in these deep and homogeneous bottom waters reveal significant vertical excursions with periods of about 50 days. The observed isopycnal displacements have amplitudes up to 100 m at the top boundary of the bottom layer; moored profiler measurements in the intermediate water column indicate that the amplitudes of these vertical displacements decay toward the surface over a scale of about 1000 m. The subinertial excursions are consistent with a bottom-trapped topographic Rossby wave. Given the magnitude of the bottom slope in the vicinity of the mooring, the observed vertical velocities correspond to only weak (about 1 cm s −1 ) cross-slope horizontal velocities. The generation mechanism for the waves remains an open question.

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“…While the early laboratory experiments tended to support the 4/3 flux law (e.g. Schmitt 1979a) within the margins of the experimental and statistical error, questions have been raised with regard to its generality (Kelley et al 2003). The laboratory values of C S have been found to overestimate the oceanic fluxes by at least an order of magnitude, a discrepancy that may indicate that the effective exponent of the flux law realized in the oceanic conditions exceeds 4/3.…”

Section: Flux Lawsmentioning

confidence: 99%

What determines the thickness of layers in a thermohaline staircase?

Radko¹

2005

J. Fluid Mech.

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A simple theory is developed for the equilibrium height of steps in a thermohaline staircase. The model is based on a linear stability analysis for a series of salt-finger interfaces, which reveals a tendency for the staircase to evolve in time until the characteristic thickness of layers reaches a critical value (H 0 ). Relatively thin layers successively merge as a result of the parametric variation of the heat/salt flux ratio (γ ), but these mergers cease when the thickness of layers exceeds H 0 . The equilibration of thick steps in our model is caused by the slight inhomogeneity of the convecting layers which has a stabilizing effect on the staircase. The instability theory is successfully tested against fully nonlinear numerical simulations and is qualitatively consistent with oceanic observations.

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The diffusive regime of double-diffusive convection

Cited by 169 publications

References 130 publications

Applicability and failure of the flux-gradient laws in double-diffusive convection

Applicability and failure of the flux-gradient laws in double-diffusive convection

Moored observations of bottom-intensified motions in the deep Canada Basin, Arctic Ocean

What determines the thickness of layers in a thermohaline staircase?

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