Journal ArticleDOI
Double diffusion in oceanography
TLDR
Turner et al. as mentioned in this paper showed how opposing stratifications of two component species could drive convection if their diffusivities differed, and they also identified the potential for the oscillatory instability when cold, fresh water overlies warm, salty water.Abstract:
The modern study of double-diffusive convection began with Melvin Stern's article on "The Salt Fountain and Thermohaline Convection" in 1960. In that paper, he showed how opposing stratifications of two component species could drive convection if their diffusivities differed. Stommel ct al (1956) had earlier noted that there was significant potential energy available in the decrease of salinity with depth found in much of the tropical and subtropical ocean. While they suggested that a flow (the salt fountain) would be driven in a thermally-conducting pipe, it was Stern who realized that the two orders of magnitude difference in heat and salt diffusivities allowed the ocean to form its own pipes. These later came to be known as "salt fingers." Stern also identified the potential for the oscillatory instability when cold, fresh water overlies warm, salty water in the 1960 paper, though only in a footnote. Turner & Stommel (1964) demonstrated the "diffusive-convection" process a few years later. From these beginnings in oceanography over three decades ago, double diffusion has come to be recognized as an important convection process in a wide variety of fluid media, including magmas, metals, and stellar interiors (Schmitt 1983, Turner 1985). However, it is interesting to note that about one hundred years before Stern's paper, W. S. Jevons (1857) reported on the observation of long, narrow convection cells formed when warm, salty water was introduced over cold, fresh water. He correctly attributed the phenomenon to a difference in the diffusivities for heat andread more
Citations
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Journal ArticleDOI
Open-ocean convection: Observations, theory, and models
John Marshall,Friedrich Schott +1 more
TL;DR: In this article, the authors review what is known about the convective process in the open ocean, in which the properties of large volumes of water are changed by intermittent, deep-reaching convection, triggered by winter storms.
Journal ArticleDOI
On the driving processes of the Atlantic meridional overturning circulation
Till Kuhlbrodt,Alexa Griesel,Marisa Montoya,Anders Levermann,Matthias Hofmann,Stefan Rahmstorf +5 more
TL;DR: In this paper, the authors review both observational data and model results concerning the two main candidates: vertical mixing processes in the ocean's interior and wind-induced Ekman upwelling in the Southern Ocean.
Journal ArticleDOI
Mixing of a tracer in the pycnocline
TL;DR: A patch of sulfur hexafluoride was released in May 1992 in the eastern North Atlantic on an isopycnal surface near 300 m depth and was surveyed over a period of 30 months as it dispersed across and along isopyncal surfaces as discussed by the authors.
Journal ArticleDOI
Interiors of Giant Planets Inside and Outside the Solar System
TL;DR: In this paper, the structure and composition of the giant planets is rapidly evolving because of high-pressure experiments with the ability to study metallic hydrogen and define the properties of its equation of state and spectroscopic and in situ measurements made by telescopes and satellites.
Book
The Turbulent Ocean
TL;DR: The Turbulent Ocean as discussed by the authors describes the principal dynamic processes that control the distribution of turbulence, its dissipation of kinetic energy and its effects on the dispersion of properties such as heat, salinity, and dissolved or suspended matter in the deep ocean, the shallow coastal and the continental shelf seas.
References
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Journal ArticleDOI
Estimates of the Local Rate of Vertical Diffusion from Dissipation Measurements
TL;DR: In this article, two models for the source of oceanic turbulence are considered; namely, production by the Reynolds stress working against a time variable mean shear, and the gravitational collapse of Kelvin-Helmholtz instabilities.
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Scaling turbulent dissipation in the thermocline
Abstract: By comparing observations from six diverse sites in the mid-latitude thermocline, we find that, to within a factor of 2, 〈eIW〉=7×10‐10〈N2/N02〉〈S104/SGM4〉 W kg‐1, where 〈eIW〉 is the average dissipation rate attributable to internal waves; N0 = 0.0052 s−1 is a reference buoyancy frequency; S10 is the observed shear having vertical wavelengths greater than 10 m; and SGM is the corresponding shear in the Garrett and Munk spectrum of internal waves. The functional form agrees with estimates by McComas and Muller and by Henyey, Wright, and Flatte of the rate of energy transfer within the internal wave spectrum, provided the energy density of the internal waves is treated as a variable instead of one of the constant parameters. Following Garrett and Munk, we assume that 〈S104/SGM4〉=〈EIW2/EGM2〉, where EIW is the observed energy density and EGM is the energy density used by Garrett and Munk. The magnitude of eIW is twice that of Henyey et al. and one third that of McComas and Muller. Thus the observations agree with predictions sufficiently well to suggest that (1) a first-order understanding of the link between internal waves and turbulence has been achieved, although Henyey et al. made some ad hoc assumptions and Garrett and Munk's model does not match important features in the internal wave spectrum reported by Pinkel, and (2) the simplest way to obtain average dissipation rates over large space and time scales is to measure 〈N2/N02〉〈S104/SGM4〉. Even though the observations were taken at latitudes of 42°−11.5°, the variability in the Coriolis parameter ƒ was too limited for a conclusive test of the ƒ dependence also predicted for 〈eIW〉 by the wave-wave interaction models. An exception to the scaling occurs east of Barbados in the thermohaline staircase that is apparently formed and maintained by salt fingers. Although e in the staircase is very low compared with rates at mid-latitude sites, it is 8 times larger than predicted for e due only to internal waves.
Journal ArticleDOI
Oceanic fine structure
Thomas R. Osborn,Charles S. Cox +1 more
TL;DR: In this paper, the vertical component of the oceanic temperature gradient is studied and the temperature changes are concentrated into regions on the order of a meter thick wherein the measured gradients are often more than ten times the average gradient and the horizontal extent of high gradient is greater than 750 meters in the seasonal thermocline off San Diego, but is only a few hundred meters at depths greater than 400 meters.
Journal ArticleDOI
The “Salt-Fountain” and Thermohaline Convection
TL;DR: In this paper, the authors discuss the stability characteristic and the form of convective motion in the laminar regime of a convective model for vertical mixing of the sea and show that the model is unstable due to the fact that the molecular diffusivity of heat is much greater than the diffusivities of salt.
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On thermohaline convection with linear gradients
Peter G. Baines,A. E. Gill +1 more
TL;DR: In this article, the thermohaline stability problem was examined in greater detail, and the most unstable mode over all wave-numbers for each R, Rs was found and it was shown that where both unstable direct and oscillating modes are present, the most stable mode is direct in most cases.