The role of double diffusion in a Gulf Stream frontal intrusion

Williams, Antony J.

doi:10.1029/jc086ic03p01917

Cited by 42 publications

(8 citation statements)

References 16 publications

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“…Because compositional convection plays an important role in a gulf stream frontal intrusion [6,63]. Such kind of frontal intrusion can be described clearly by the present model (please see Figs.…”

Section: Resultssupporting

confidence: 51%

Simulating compositional convection in the presence of rotation by lattice Boltzmann model

Chen

2010

International Journal of Thermal Sciences

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Section: Resultssupporting

confidence: 51%

Simulating compositional convection in the presence of rotation by lattice Boltzmann model

Chen

2010

International Journal of Thermal Sciences

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“…Such features are generally referred to as intrusions. Intrusions have been observed at the edge of Meddies (Hebert et al 1990;Ruddick 1992), in the Arctic Ocean (Perkin and Lewis 1984;Rudels et al 1998), in the equatorial Pacific Ocean (Toole 1981;Richards and Banks 2002), at the Antarctic polar front (Joyce et al 1978;Georgi 1978), and in the Gulf Stream (Joyce 1976;Williams 1981). Their vertical scales range from 2 m within the thermocline to 250 m in deep water, and coherent features have been tracked laterally for up to 200 km in the equatorial Pacific and for over 1000 km in the Arctic Ocean.…”

Section: Introductionmentioning

confidence: 94%

Is Interleaving in the Agulhas Current Driven by Near-Inertial Velocity Perturbations?

Beal

2007

Journal of Physical Oceanography

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Recent observations taken at a number of latitudes in the Agulhas Current reveal that the water mass structure on either side of its dynamical core is distinctly different. Moreover, interleaving of these distinct water masses is observed at over 80% of the stations occupied in the current, particularly within the subsurface density layer between tropical surface water and subtropical surface water masses, and within the intermediate layer between the Antarctic Intermediate Water and Red Sea water masses. Direct velocity measurements allow for a comparison between the characteristic vertical length scales of the Agulhas intrusions and those of velocity perturbations found throughout the current. It is found that the interleaving scales match those of the velocity perturbations, which are manifest as high-wavenumber vertical shear layers and are identified as near-inertial oscillations. Furthermore, the properties of the intrusions indicate that double diffusion is not an important process in their development: they are generally not associated with a density anomaly, their slope and thickness fall outside the predicted maxima for instability, and a strong horizontal shear field acts to separate water parcels more quickly than intrusions would be able to grow by double-diffusive processes. Instead, the position, thickness, and slope of Agulhas intrusions relative to the background salinity and density field suggest that they are forced by rotating inertial velocities, with subsequent growth possibly driven by small-scale baroclinic instabilities. However, not all the evidence points conclusively toward advectively driven intrusions. For instance, there is a discrepancy between the observed salinity anomaly amplitude and the predicted inertial displacement given the background salinity gradient, which deserves further examination. Hence, there is a future need for more pointed observations and perhaps the development of an analytical or numerical model to understand the exact nature of Agulhas intrusions.

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“…The fluids are stirred by advective shear instabilities then mixed by diffusion. Assuming no turbulent diffusion, the final temperature and specific conductance that would result from double diffusion between two well-mixed intrusive water masses can be estimated by using the initial conditions of temperature and specific conductance and equations for the temperature, T(z,t), and the specific conductance, S(z,t), which are error functions of the distance away from the interface, z, and the time, t [Williams, 1981]: Visual observations show that the interface is convoluted laterally into vortex-like filaments.…”

Section: Discussionmentioning

confidence: 99%

“…Heat diffuses first because the diffusivity for heat is approximately 100 times the diffusivity for dissolved solids [Thorpe, etal., 1969;Williams, 1981]. This component may act independently or in concert with the lateral shear to deform the interface and to produce interleaving intrusions with a corresponding increase in surface area.…”

Section: Discussionmentioning

confidence: 99%

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Observations of Mixing Processes Downstream from the Confluence of the Mississippi and St. Croix Rivers

Moody

2013

Geophysical Monograph Series

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The initial lateral mixing downstream from a confluence of two rivers with different water proper ties and velocities has a near-field mixing zone that is typically 5-10 river widths long and visually similar to the free shear-flow zone in an infinitely deep fluid. Vertical and horizontal profiles, and time-series measurements of temperature and specific conductance were collected in the near-field mixing zone at three distances downstream from the confluence of the Mississippi and St. Croix Riv ers on April 11, 1992. The vertical interface between the two fluids was characterized by step-like gradients in color, temperature, specific conductance, and velocity. Mixing in the near-field zone con sisted of stirring and diffusion processes. The difference in velocity between the two fluids (0.18 m/ s) created lateral shear instabilities that were visible at the surface and appeared to have 3-dimensional structure. These instabilities stirred the water, increasing the surface area of the interface, and created horizontal intrusions of water with temperature and specific-conductance properties that con trasted with the surrounding water. Twenty meters downstream from the confluence (about 0.05 river widths), the downstream size of these intrusions was 10-80 m and the vertical size was 0.2-0.5 m. There were sharp gradients of temperature and specific conductance across the horizontal interface between the intrusions and surrounding fluid (differences of 3.4°C and 500 uS/cm), and measure ments made inside some intrusions suggest that mixing at the edges of these intrusions was double diffusive. Double diffusion may have coupled with the shear (estimated gradient Richardson number was 0.2) to produce triple diffusion. Turbulent instabilities continued to stir the water causing the intrusions to decrease in size downstream such that the final measurements of temperature and spe cific conductance about 8 river widths downstream from the confluence were relatively smooth, monotonic functions of the cross-channel distance.

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The role of double diffusion in a Gulf Stream frontal intrusion

Cited by 42 publications

References 16 publications

Simulating compositional convection in the presence of rotation by lattice Boltzmann model

Simulating compositional convection in the presence of rotation by lattice Boltzmann model

Is Interleaving in the Agulhas Current Driven by Near-Inertial Velocity Perturbations?

Observations of Mixing Processes Downstream from the Confluence of the Mississippi and St. Croix Rivers

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