scholarly journals Cold-Water Events and Dissipation in the Mixed Layer of a Lake

2006 ◽  
Vol 36 (10) ◽  
pp. 1928-1939 ◽  
Author(s):  
B. Ozen ◽  
S. A. Thorpe ◽  
U. Lemmin ◽  
T. R. Osborn
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Mixed Layer ◽  
Large Scale ◽  
Cold Water ◽  
Velocity Shear ◽  
Surface Mixed Layer ◽  
Near Surface ◽  
Law Of The Wall ◽  
Upward Direction

Abstract Measurements of temperature, velocity, and microscale velocity shear were made from the research submarine F. A. Forel in the near-surface mixed layer of Lake Geneva under conditions of moderate winds of 6–8 m s−1 and of net heating at the water surface. The submarine carried arrays of thermistors and a turbulence package, including airfoil shear probes. The rate of dissipation of turbulent kinetic energy per unit mass, estimated from the variance of the shear, is found to be lognormally distributed and to vary with depth roughly in accordance with the law of the wall at the measurement depths, 15–20 times the significant wave height. Measurements revealed large-scale structures, coherent over the 2.38-m vertical extent sampled by a vertical array of thermistors, consisting of filaments tilted in the wind direction. They are typically about 1.5 m wide, decreasing in width in the upward direction, and are horizontally separated by about 25 m in the downwind direction. Originating in the upper thermocline, they are characterized in the mixed layer by their relatively low temperature and low rates of dissipation of turbulent kinetic energy and by an upward vertical velocity of a few centimeters per second.

scholarly journals A New Look at Richardson Number Mixing Schemes for Equatorial Ocean Modeling

2009 ◽  
Vol 39 (10) ◽  
pp. 2652-2664 ◽  
Author(s):  
Edward D. Zaron ◽  
James N. Moum
Keyword(s):  
Heat Flux ◽  
Kinetic Energy ◽  
Mixed Layer ◽  
Richardson Number ◽  
Large Scale ◽  
Ocean Modeling ◽  
Depth Range ◽  
Surface Mixed Layer ◽  
Flux Divergence ◽  
Equatorial Undercurrent

Abstract A reexamination of turbulence dissipation measurements from the equatorial Pacific shows that the turbulence diffusivities are not a simple function of the gradient Richardson number. A widely used mixing scheme, the K-profile parameterization, overpredicts the turbulent vertical heat flux by roughly a factor of 4 in the stably stratified region between the surface mixed layer and the Equatorial Undercurrent (EUC). Additionally, the heat flux divergence is of the incorrect sign in the upper 80 m. An alternative class of parameterizations is examined that expresses the mixing coefficients in terms of the large-scale kinetic energy, shear, and Richardson number. These representations collapse the turbulence diffusivities above and below the Equatorial Undercurrent, and a tuned version is able to reproduce the vertical turbulence heat flux within the 50–180-m depth range. Kinetic energy is not Galilean invariant, so the collapse of the data with the new parameterization suggests that oceanic turbulence responds to boundary forcing at depths well below the surface mixed layer.

scholarly journals Wave-turbulence scaling in the ocean mixed layer

Ocean Science ◽  
2013 ◽  
Vol 9 (4) ◽  
pp. 597-608 ◽  
Author(s):  
G. Sutherland ◽  
B. Ward ◽  
K. H. Christensen
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Energy Dissipation Rate ◽  
Wall Layer ◽  
Near Surface ◽  
Microstructure Measurements ◽  
Oceanic Boundary Layer

Abstract. Microstructure measurements were collected using an autonomous freely rising profiler under a variety of different atmospheric forcing and sea states in the open ocean. Here, profiles of turbulent kinetic energy dissipation rate, ε, are compared with various proposed scalings. In the oceanic boundary layer, the depth dependence of ε was found to be largely consistent with that expected for a shear-driven wall layer. This is in contrast with many recent studies which suggest higher rates of turbulent kinetic energy dissipation in the near surface of the ocean. However, some dissipation profiles appeared to scale with the sum of the wind and swell generated Stokes shear with this scaling extending beyond the mixed layer depth. Integrating ε in the mixed layer yielded results that 1% of the wind power referenced to 10 m is being dissipated here.

scholarly journals Wave-turbulence scaling in the ocean mixed layer

2012 ◽  
Vol 9 (6) ◽  
pp. 3761-3793
Author(s):  
G. Sutherland ◽  
K. H. Christensen ◽  
B. Ward
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Energy Dissipation Rate ◽  
Wall Layer ◽  
Stokes Drift ◽  
Near Surface ◽  
Oceanic Boundary Layer

Abstract. Microstructure measurements were collected using an autonomous freely rising profiler under a variety of different atmospheric forcing and sea states in the open ocean. Here, profiles of turbulent kinetic energy dissipation rate, ε, are compared with various proposed scalings. In the oceanic boundary layer, the depth dependence of ε was found to be consistent with that expected for a purely shear-driven wall layer. This is in contrast with many recent studies which suggest higher rates of turbulent kinetic energy dissipation in the near surface of the ocean. However, many dissipation profiles scaled with a Stokes drift-generated shear, suggesting there may be occasions where the shear in the mixed layer are dominated by wave-induced currents, which often causes turbulence to extend beyond the mixed layer depth. Integrating ε in the mixed layer yielded results that 1% of the wind power referenced to 10 m is being dissipated here.

scholarly journals Physical Transport Processes that Affect the Distribution of Oil in the Gulf of Mexico: Observations and Modeling

Oceanography ◽  
2021 ◽  
Vol 34 (1) ◽  
pp. 58-75
Author(s):  
Michel Boufadel ◽  
◽  
Annalisa Bracco ◽  
Eric Chassignet ◽  
Shuyi Chen ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Physical Environment ◽  
Large Scale ◽  
Transport Processes ◽  
Small Scale ◽  
Surface Mixed Layer ◽  
Physical Processes ◽  
Mixing Processes ◽  
Near Surface ◽  
Wide Range

Physical transport processes such as the circulation and mixing of waters largely determine the spatial distribution of materials in the ocean. They also establish the physical environment within which biogeochemical and other processes transform materials, including naturally occurring nutrients and human-made contaminants that may sustain or harm the region’s living resources. Thus, understanding and modeling the transport and distribution of materials provides a crucial substrate for determining the effects of biological, geological, and chemical processes. The wide range of scales in which these physical processes operate includes microscale droplets and bubbles; small-scale turbulence in buoyant plumes and the near-surface “mixed” layer; submesoscale fronts, convergent and divergent flows, and small eddies; larger mesoscale quasi-geostrophic eddies; and the overall large-scale circulation of the Gulf of Mexico and its interaction with the Atlantic Ocean and the Caribbean Sea; along with air-sea interaction on longer timescales. The circulation and mixing processes that operate near the Gulf of Mexico coasts, where most human activities occur, are strongly affected by wind- and river-induced currents and are further modified by the area’s complex topography. Gulf of Mexico physical processes are also characterized by strong linkages between coastal/shelf and deeper offshore waters that determine connectivity to the basin’s interior. This physical connectivity influences the transport of materials among different coastal areas within the Gulf of Mexico and can extend to adjacent basins. Major advances enabled by the Gulf of Mexico Research Initiative in the observation, understanding, and modeling of all of these aspects of the Gulf’s physical environment are summarized in this article, and key priorities for future work are also identified.

scholarly journals Diurnal Dynamics of the Umov Kinetic Energy Density Vector in the Atmospheric Boundary Layer from Minisodar Measurements

Atmosphere ◽  
2021 ◽  
Vol 12 (10) ◽  
pp. 1347
Author(s):  
Alexander Potekaev ◽  
Nikolay Krasnenko ◽  
Liudmila Shamanaeva
Keyword(s):  
Energy Density ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Energy Flux ◽  
Wind Effect ◽  
Kinetic Energy Density ◽  
Near Surface ◽  
Density Vector ◽  
The Mean ◽  
Umov Vector

The diurnal hourly dynamics of the kinetic energy flux density vector, called the Umov vector, and the mean and turbulent components of the kinetic energy are estimated from minisodar measurements of wind vector components and their variances in the lower 200-meter layer of the atmosphere. During a 24-hour period of continuous minisodar observations, it was established that the mean kinetic energy density dominated in the surface atmospheric layer at altitudes below ~50 m. At altitudes from 50 to 100 m, the relative contributions of the mean and turbulent wind kinetic energy densities depended on the time of the day and the sounding altitude. At altitudes below 100 m, the contribution of the turbulent kinetic energy component is small, and the ratio of the turbulent to mean wind kinetic energy components was in the range 0.01–10. At altitudes above 100 m, the turbulent kinetic energy density sharply increased, and the ratio reached its maximum equal to 100–1000 at altitudes of 150–200 m. A particular importance of the direction and magnitude of the wind effect, that is, of the direction and magnitude of the Umov vector at different altitudes was established. The diurnal behavior of the Umov vector depended both on the time of the day and the sounding altitude. Three layers were clearly distinguished: a near-surface layer at altitudes of 5–15 m, an intermediate layer at altitudes from 15 m to 150 m, and the layer of enhanced turbulence above. The feasibility is illustrated of detecting times and altitudes of maximal and minimal wing kinetic energy flux densities, that is, time periods and altitude ranges most and least favorable for flights of unmanned aerial vehicles. The proposed novel method of determining the spatiotemporal dynamics of the Umov vector from minisodar measurements can also be used to estimate the effect of wind on high-rise buildings and the energy potential of wind turbines.

Large-scale modes of turbulent channel flow: transport and structure

2001 ◽  
Vol 448 ◽  
pp. 53-80 ◽  
Author(s):  
Z. LIU ◽  
R. J. ADRIAN ◽  
T. J. HANRATTY
Keyword(s):  
Shear Stress ◽  
Kinetic Energy ◽  
Shear Layer ◽  
Turbulent Kinetic Energy ◽  
Large Scale ◽  
Reynolds Shear Stress ◽  
Reynolds Numbers ◽  
Upstream Region ◽  
Two Dimensional ◽  
Normal Plane

Turbulent flow in a rectangular channel is investigated to determine the scale and pattern of the eddies that contribute most to the total turbulent kinetic energy and the Reynolds shear stress. Instantaneous, two-dimensional particle image velocimeter measurements in the streamwise-wall-normal plane at Reynolds numbers Reh = 5378 and 29 935 are used to form two-point spatial correlation functions, from which the proper orthogonal modes are determined. Large-scale motions – having length scales of the order of the channel width and represented by a small set of low-order eigenmodes – contain a large fraction of the kinetic energy of the streamwise velocity component and a small fraction of the kinetic energy of the wall-normal velocities. Surprisingly, the set of large-scale modes that contains half of the total turbulent kinetic energy in the channel, also contains two-thirds to three-quarters of the total Reynolds shear stress in the outer region. Thus, it is the large-scale motions, rather than the main turbulent motions, that dominate turbulent transport in all parts of the channel except the buffer layer. Samples of the large-scale structures associated with the dominant eigenfunctions are found by projecting individual realizations onto the dominant modes. In the streamwise wall-normal plane their patterns often consist of an inclined region of second quadrant vectors separated from an upstream region of fourth quadrant vectors by a stagnation point/shear layer. The inclined Q4/shear layer/Q2 region of the largest motions extends beyond the centreline of the channel and lies under a region of fluid that rotates about the spanwise direction. This pattern is very similar to the signature of a hairpin vortex. Reynolds number similarity of the large structures is demonstrated, approximately, by comparing the two-dimensional correlation coefficients and the eigenvalues of the different modes at the two Reynolds numbers.

Coherent Velocity Structures in the Mixed Layer: Characteristics, Energetics, and Turbulent Kinetic Energy Budget

2021 ◽  
Author(s):  
Ewa Jarosz ◽  
Hemantha W. Wijesekera ◽  
David W. Wang
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Mixed Layer ◽  
Vertical Velocity ◽  
Mixed Layer Depth ◽  
Vertical Transport ◽  
Rate Of Change ◽  
Production Term ◽  
Forcing Mechanisms ◽  
Surface Buoyancy

AbstractVelocity, hydrographic, and microstructure observations collected under moderate to high winds, large surface waves, and significant ocean-surface heat losses were utilized to examine coherent velocity structures (CVS) and turbulent kinetic energy (TKE) budget in the mixed layer on the outer shelf in the northern Gulf of Mexico in February 2017. The CVS exhibited larger downward velocities in downweling regions and weaker upward velocities in broader upwelling regions, elevated vertical velocity variance, vertical velocity maxima in the upper part of the mixed layer, and phasing of crosswind velocities relative to vertical velocities near the base of the mixed layer. Temporal scales ranged from 10 min to 40 min and estimated lateral scales ranged from 90 m to 430 m, which were 1.5 – 6 times larger than the mixed layer depth. Nondimensional parameters, Langmuir and Hoenikker numbers, indicated that plausible forcing mechanisms were surface-wave driven Langmuir vortex and destabilizing surface buoyancy flux. The rate of change of TKE, shear production, Stokes production, buoyancy production, vertical transport of TKE, and dissipation in the TKE budget were evaluated. The shear and Stokes productions, dissipation, and vertical transport of TKE were the dominant terms. The buoyancy production term was important at the sea surface, but it decreased rapidly in the interior. A large imbalance term was found under the unstable, high wind, and high-sea state conditions. The cause of this imbalance cannot be determined with certainty through analyses of the available observations; however, our speculation is that the pressure transport is significant under these conditions.

Pelagic primary production in the Coral and southern Solomon Seas

1996 ◽  
Vol 47 (5) ◽  
pp. 695 ◽  
Author(s):  
MJ Furnas ◽  
AW Mitchell
Keyword(s):  
Primary Production ◽  
Mixed Layer ◽  
Standing Crop ◽  
Central Basin ◽  
Strong Wind ◽  
Surface Mixed Layer ◽  
Barrier Reef ◽  
Near Surface ◽  
Western Margin ◽  
Coral Sea

Phytoplankton primary production was measured around the periphery of the Coral Sea during October 1985 and in the boundary current systems bordering the northern Australian Great Barrier Reef (GBR) and Papuan Barrier Reef (PBR) during October 1985 and June-July 1988. Under strong wind conditions (mean winds 8-12 m s-1), the north-western Papuan Barrier Reef region was characterized by a shallow surface mixed layer, shallow nutriclines (25-75 m) and shallow subsurface chlorophyll maxima. Under low wind stress conditions (mean winds <5 m s-1), the southern and western Coral Sea were also characterized by a shallow surface mixed layer and stable underlying density profiles but deep (>I00 m) nutriclines and deep (60-125 m) subsurface chlorophyll and primary production maxima. Regardless of location, most primary production occurred above the 20% mid-day isolume surface. Phytoplankton standing crop and primary production in all regions were dominated by picoplankton (<2 μm size fraction). Very high primary production rates (1-3 g C m-2 day-1) were measured at a number of stations adjacent to the western margin of the PBR and within the central basin of the Louisiade Archipelago. Evidence for upwelling along the western margin of the PBR was observed under both north-easterly (normal to the reef axis) and south-easterly (parallel to the reef axis) wind regimes; however, surface outcropping of upwelled water did not occur. Oceanic primary production in the Coral Sea is estimated to be between 100 and 200 g C m-2 year-1. Primary production in and around the Louisiade Archipelago appears to be on the order of 200-300 g C m-2 year-1. Near-surface chlorophyll standing crop was generally better correlated with near-surface primary production than was total chlorophyll with total areal primary production.

Onset of stratification in a mixed layer subjected to a stabilizing buoyancy flux

1995 ◽  
Vol 304 ◽  
pp. 27-46 ◽  
Author(s):  
Y. Noh ◽  
H. J. S. Fernando
Keyword(s):  
Numerical Model ◽  
Kinetic Energy ◽  
Laboratory Experiment ◽  
Water Column ◽  
Turbulent Kinetic Energy ◽  
Energy Flux ◽  
Mixed Layer ◽  
Mixed State ◽  
Buoyancy Flux ◽  
Tidal Front

The formation of a thermocline in a water column, in which shear-free turbulence is generated both at the surface and bottom, and a stabilizing buoyancy flux is imposed at the surface, is studied using a laboratory experiment and a numerical model with the aim of understanding the formation of a tidal front in coastal seas. The results show that the formation of a thermocline, which always occurs in the absence of bottom mixing, is inhibited and the water column maintains a vertically mixed state, when bottom mixing becomes sufficiently strong. It is found from both experimental and numerical results that the criterion for the formation of a thermocline is determined by the balance between the rate of work that is necessary to maintain a mixed state against the formation of stratification by the buoyancy flux and the turbulent kinetic energy flux from the bottom supplied to the depth of thermocline formation. The depth of the thermocline, when it is formed, is found to decrease with bottom mixing.

Sign in / Sign up

Export Citation Format

Share Document