Images of ocean microstructure

Williams, Antony J.

doi:10.1016/0011-7471(75)90085-6

Cited by 30 publications

(41 citation statements)

References 23 publications

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“…This limited range of allowable flux ratios and wavenumbers is the likely explanation for the increasing order displayed in finger planforms as experiments run down and the density ratio approaches its upward limit and one wavenumber comes to dominate the field (Williams, 1975). Strongly forced fingers at low density ratios are much more irregular in appearance, and numerical simulations display increasingly chaotic and turbulent appearing structures as R ρ → 1.…”

Section: The Long Finger Solutionsmentioning

confidence: 99%

“…Here we have used sin(kx) sin(ky) as a simple solution to the Helmholtz equation (∇ 2 φ + k 2 φ = 0) that yields square packed fingers, a planform that is observed in the later stages of laboratory experiments (Williams, 1975). Schmitt (1994a) has shown that a rich variety of finger planforms are available to satisfy the Helmholtz equation, but this has no impact on the essential relation between growth and the total horizontal wavenumber.…”

Section: The Long Finger Solutionsmentioning

confidence: 99%

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Thermohaline convection at density ratios below one: A new regime for salt fingers

Schmitt¹

2011

j mar res

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New experimental results on haline convection show a surprising preference for narrow fingers over large-scale convection when even a small stabilizing temperature gradient is present (Hage and Tilgner, 2010). This regime has heat/salt density ratios below one, a parameter range that has not been explored in traditional salt finger theory. Here the properties of the exact (long finger) solutions of Schmitt (1979Schmitt ( , 1983) are explored at low density ratios. It is found that narrow finger solutions are indeed obtained and remain the fastest growing in some circumstances, though the selective advantage of the "Stern scale" can disappear as the density ratio decreases. The variation of solutions with Prandtl number and the relation to the Stern (1975) approximate solution are examined and discussed.

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Section: The Long Finger Solutionsmentioning

confidence: 99%

Section: The Long Finger Solutionsmentioning

confidence: 99%

Thermohaline convection at density ratios below one: A new regime for salt fingers

Schmitt¹

2011

j mar res

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“…Secondly, the series of steps and layers observed in regions of the ocean where the vertical temperature and salinity gradients have the same sign (Tait and Howe, 1968, Molcard and Williams, 1975, Williams, 1975, Lambert and Sturges, 1977 have been interpreted as finite amplitude signatures of double diffusion (Turner, 1973).…”

Section: (1978)mentioning

confidence: 99%

“…Although the exact value of the critical wavelength is uncertain due to the poor estimates of Av and As, the dependence of this vertical wavelength to the external parameters e and e may be compared to the x z laboratory work. One of the major observations in the laboratory experiments is that a direct relation exists between the vertical wavelength, H, and C (Turner and Ruddick, 1979 Williams, 1975) was unimportant to the behavior of 50 m high intrusions, the parameterization of the salt finger physics was retained and more complex models of oceanic intrusions were examined.…”

Section: 17mentioning

confidence: 99%

Wintertime convection and frontal interleaving in the Southern Ocean

Toole¹

1980

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The Southern Ocean as defined here is the body of water between the Antarctic Continent and the Antarctic Polar Front, (APF).This ocean is considered important in the global thermodynamic balance of the ocean-atmosphere system because large planetary heat losses are believed to occur at high latitudes.The ocean and atmosphere must transport heat poleward to balance these losses.In the Southern Hemisphere, the oceanic contribution to this flux involves a southward transport of heat across the APF into the Southern Ocean where it is given up to the atmosphere through air-sea interactions.In Part I, the air-sea interactions and structure of the' near surface waters of the Southern Ocean are investigated with a three dimensional time dependent numerical model.The surface waters in this region in summer are characterized by a relatively warm surface mixed layer with low salinity.Below this layer, a cold temperature extremum is usually observed in vertical profiles which is believed to be the remnant of a deep surface mixed layer produced in winter.The characteristics of this layer, the surface mixed layer and the observed distribution of wintertime sea ice are reproduced well by this model.Unlike some other sea-ice models the air-sea heat exchange is a free variable.Model estimates of the annual heat loss by the Southern Ocean exhibit the observed meridional variation of heat gained by the ocean along the APF with heat lost further south.The model's area average heat loss is much smaller than that estimated with direct observations. While several model parameterizations were made which could be in error, the model results suggest that the Southern Ocean does give up vast amounts of heat to the atmosphere away from the continental margins.The model results and direct calculations of air-sea exchanges suggest a southward heat flux must occur across the APF.The lateral water mass transition across the front is not discontinuous but occurs over a finite sized zone of fluid which is dominated by intrusive finestructure.The characteristics and dynamics of these features are investigated in Part II to try and assess their importance in the meridional heat budget. Abstract (Contd.)Observations made on two cruises to the APF are presented and the space-time scales of the features and thermohaline characteristics are discussed. It is suggested that double diffusive processes dominated by salt fingering are active within the intrusions.An extension of Stern's (1967) model of the stability of a thermohaline front to intrusive finestructure driven by saltfingering where-small scale viscous processes are included, is presented to explain why intrusions are observed in frontal zones.The model successfully predicts vertical scales of intrusions observed in the ocean and the observed dependence of the intrusions' slopes across density surfaces on the vertical scale.Since the fastest growing intrusion is not strongly determined by the model, though, it is likely that finite amplitude effects determine the dominant scale of int...

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“…The OSFD was originally designed to photograph salt fingers in the ocean (Williams, 1975). They are visible because rising and sinking fingers have different indices of refraction and because a group of salt fingers forms an orderly array.…”

Section: Optical Salt Finger Detectormentioning

confidence: 99%

Finestructure and turbulence in the deep ocean

Hendricks¹

1977

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Millimeter scale fluctuations in refractive index recorded with a freely sinking shadowgraph system are correlated with finestructure profiles of temperature, salinity and density and compared to models 0·£ ocean turbulence. Imag.es wi th ·vertically aligned periodic structure, called bands, are identified as salt fingers, while others with chaotic 'structure are turbulent.Images are found on interfaces that are I-10m thick and have gradients at least several times the mean. From 6 profiles in the Mediterranean Outflow region of the eastern North Atlantic between 1.0 and l.~km depth, 398 interfaces have been identified and a significant fraction (about 1/3) of these have detectable images. High contrast images, including bands, are most often found below warm, .saline intrusions and within stepped structure where there is a regular sequence of homogeneous mixed layers separated by interfaces. As the interfacial salinity gradient increases in the sense that allows salt finger convection, the fraction of interfaces with images increases. The horizontal spacing of bands ('\1 5 nun) is consistent with calculated salt finger diameter. The calculated and observed length of ocean salt fingers (10-20 cm) is a small fraction of the interface thickness.High levels of small scale variability in the shadowgraphs is reflected in high levels of variance' in the finestructure band of the temperature spectra. The temperature gradient spectra have a slope of -1, indicative of turbulence affected by buoyancy forces, and there is a relative peak at a wavelength near the observed salt finger length.The high contrast images are found at interfaces within the enhanced mean salinity gradient below saline intrusions. For very strong salinity gradien.ts there is a solitary interface with intense images, but for weaker mean gradients the convection takes the form of stepped structure. The steps may evolve from the solitary interface as the salinity gradient is run down by salt finger convection.This study identifies parts of the ocean where salt finger convection is prevalent and includes the first comprehensive description of salt fingers in the ocean. Existing models of salt fingers are evaluated in light of ocean observations, and models of ocean turbulence are compared to measurements.

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Images of ocean microstructure

Cited by 30 publications

References 23 publications

Thermohaline convection at density ratios below one: A new regime for salt fingers

Thermohaline convection at density ratios below one: A new regime for salt fingers

Wintertime convection and frontal interleaving in the Southern Ocean

Finestructure and turbulence in the deep ocean

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