Control of Large-Scale Heat Transport by Small-Scale Mixing

2006 ◽  
Vol 36 (10) ◽  
pp. 1877-1894 ◽  
Author(s):  
Paola Cessi ◽  
W. R. Young ◽  
Jeff A. Polton
Keyword(s):  
Heat Transport ◽  
Mixed Layer ◽  
Large Scale ◽  
Scaling Laws ◽  
Mechanical Energy ◽  
Small Scale ◽  
Thermocline Depth ◽  
Leading Order ◽  
Diapycnal Diffusivity ◽  
The Mean

Abstract The equilibrium of an idealized flow driven at the surface by wind stress and rapid relaxation to nonuniform buoyancy is analyzed in terms of entropy production, mechanical energy balance, and heat transport. The flow is rapidly rotating, and dissipation is provided by bottom drag. Diabatic forcing is transmitted from the surface by isotropic diffusion of buoyancy. The domain is periodic so that zonal averaging provides a useful decomposition of the flow into mean and eddy components. The statistical equilibrium is characterized by quantities such as the lateral buoyancy flux and the thermocline depth; here, scaling laws are proposed for these quantities in terms of the external parameters. The scaling theory predicts relations between heat transport, thermocline depth, bottom drag, and diapycnal diffusivity, which are confirmed by numerical simulations. The authors find that the depth of the thermocline is independent of the diapycnal mixing to leading order, but depends on the bottom drag. This dependence arises because the mean stratification is due to a balance between the large-scale wind-driven heat transport and the heat transport due to baroclinic eddies. The eddies equilibrate at an amplitude that depends to leading order on the bottom drag. The net poleward heat transport is a residual between the mean and eddy heat transports. The size of this residual is determined by the details of the diapycnal diffusivity. If the diffusivity is uniform (as in laboratory experiments) then the heat transport is linearly proportional to the diffusivity. If a mixed layer is incorporated by greatly increasing the diffusivity in a thin surface layer then the net heat transport is dominated by the model mixed layer.

scholarly journals Energetic Submesoscales Maintain Strong Mixed Layer Stratification during an Autumn Storm

2017 ◽  
Vol 47 (10) ◽  
pp. 2419-2427 ◽  
Author(s):  
Daniel B. Whitt ◽  
John R. Taylor
Keyword(s):  
Mixed Layer ◽  
North Atlantic ◽  
Small Scale ◽  
Upper Ocean ◽  
Ocean Mixed Layer ◽  
Ocean Stratification ◽  
The North ◽  
Large Eddy ◽  
The Mean ◽  
Scale Turbulence

AbstractAtmospheric storms are an important driver of changes in upper-ocean stratification and small-scale (1–100 m) turbulence. Yet, the modifying effects of submesoscale (0.1–10 km) motions in the ocean mixed layer on stratification and small-scale turbulence during a storm are not well understood. Here, large-eddy simulations are used to study the coupled response of submesoscale and small-scale turbulence to the passage of an idealized autumn storm, with a wind stress representative of a storm observed in the North Atlantic above the Porcupine Abyssal Plain. Because of a relatively shallow mixed layer and a strong downfront wind, existing scaling theory predicts that submesoscales should be unable to restratify the mixed layer during the storm. In contrast, the simulations reveal a persistent and strong mean stratification in the mixed layer both during and after the storm. In addition, the mean dissipation rate remains elevated throughout the mixed layer during the storm, despite the strong mean stratification. These results are attributed to strong spatial variability in stratification and small-scale turbulence at the submesoscale and have important implications for sampling and modeling submesoscales and their effects on stratification and turbulence in the upper ocean.

scholarly journals Comparison of the Nutrient Content of Eggs from Commercial and Village Chickens in Rural Malawi (P03-009-19)

2019 ◽  
Vol 3 (Supplement_1) ◽  
Author(s):  
Rochelle Werner ◽  
Bess Caswell ◽  
Kenneth Maleta ◽  
Christine Stewart
Keyword(s):  
Vitamin D3 ◽  
Large Scale ◽  
Nutrient Content ◽  
The United States ◽  
Water Soluble ◽  
Small Scale ◽  
Convenience Sample ◽  
Nutrient Analysis ◽  
The Mean ◽  
The Village

Abstract Objectives To characterize the nutritional composition of chicken eggs from a large-scale commercial producer and a small-scale household producer in rural Malawi. Methods A convenience sample of 28 large commercial and 32 village eggs from Malawi were hardboiled and measured for the weight in grams of the whole egg, peeled egg, egg white, and egg yolk. A separate convenience sample of 11 commercial and 17 village eggs were selected for nutrient analysis. Eggs were hardboiled for 4 minutes, refrigerated, and shipped to a nutrient analysis lab in the United States. Eggs from each source were pooled and analyzed for macronutrients, amino acids, fatty acids, vitamins, and minerals. Analytes were reported per 100 g sample and converted to nutrients per egg using the mean peeled egg weight. Results The mean weight in grams of whole commercial eggs (59.4 ± 5.3) was 19 g greater than whole village eggs (40.4 ± 3.0). Commercial eggs had a 15 g greater mass of egg whites (37.0 ± 4.2) than village eggs (21.8 ± 2.5), but the mass of egg yolks only differed by one gram (commercial: 15.3 ± 1.0 and village: 14.1 ± 1.4). Per 100 g sample, commercial and village eggs had similar calories (143 kcals vs. 162kcals), protein (12.5 g vs. 12.5 g), water-soluble vitamins (1.61 µg vs. 1.92 µg Vitamin B-12; 63.5 µg vs. 59.9 µg folate, DFE) and minerals (1.7 mg vs. 2.1 mg iron; 21 µg vs. 24 µg selenium; 1.1 mg vs. 1.4 mg zinc). For fat-soluble nutrients, the 100 g sample of commercial eggs had a higher concentration of Vitamin A than the village eggs (150 µg vs. 102 µg RAE) but lower concentrations of Vitamin D3, α-tocopherol, and choline than the village eggs (0.8 µg vs. 2.9 µg Vitamin D3; 2.25 mg vs. 4.08 mg α-tocopherol; and 238 mg vs. 314 mg choline). However, when compared on a per egg basis, the fat-soluble nutrient content of the whole eggs was similar due to the smaller size of the village eggs. Conclusions On a per egg basis, eggs from small-scale households may deliver comparable amounts of fat-soluble nutrients but fewer calories, protein, and minerals compared to eggs from commercial producers; however, on a per 100 g basis, village eggs were a more nutrient-dense option. Funding Sources The Bill and Melinda Gates Foundation, BLUM Center of UC Davis.

Salinity Variations in the Southern California Current*

2005 ◽  
Vol 35 (8) ◽  
pp. 1421-1436 ◽  
Author(s):  
Niklas Schneider ◽  
Emanuele Di Lorenzo ◽  
Pearn P. Niiler
Keyword(s):  
Large Scale ◽  
Southern California ◽  
Current System ◽  
California Current ◽  
Southern California Bight ◽  
Small Scale ◽  
Climate Indices ◽  
California Current System ◽  
The Mean ◽  
Salinity Variations

Abstract Hydrographic observations southwestward of the Southern California Bight in the period 1937–99 show that temperature and salinity variations have very different interannual variability. Temperature varies within and above the thermocline and is correlated with climate indices of El Niño, the Pacific decadal oscillation, and local upwelling. Salinity variability is largest in the surface layers of the offshore salinity minimum and is characterized by decadal-time-scale changes. The salinity anomalies are independent of temperature, of heave of the pycnocline, and of the climate indices. Calculations demonstrate that long-shore anomalous geostrophic advection of the mean salinity gradient accumulates along the mean southward trajectory along the California Current and produces the observed salinity variations. The flow anomalies for this advective process are independent of large-scale climate indices. It is hypothesized that low-frequency variability of the California Current system results from unresolved, small-scale atmospheric forcing or from the ocean mesoscale upstream of the Southern California Bight.

Generation mechanism of a hierarchy of vortices in a turbulent boundary layer

2019 ◽  
Vol 865 ◽  
pp. 1085-1109 ◽  
Author(s):  
Yutaro Motoori ◽  
Susumu Goto
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Energy Spectrum ◽  
Turbulent Boundary Layer ◽  
Large Scale ◽  
Generation Mechanism ◽  
Small Scale ◽  
Generation Process ◽  
Mean Flow ◽  
The Mean

To understand the generation mechanism of a hierarchy of multiscale vortices in a high-Reynolds-number turbulent boundary layer, we conduct direct numerical simulations and educe the hierarchy of vortices by applying a coarse-graining method to the simulated turbulent velocity field. When the Reynolds number is high enough for the premultiplied energy spectrum of the streamwise velocity component to show the second peak and for the energy spectrum to obey the$-5/3$power law, small-scale vortices, that is, vortices sufficiently smaller than the height from the wall, in the log layer are generated predominantly by the stretching in strain-rate fields at larger scales rather than by the mean-flow stretching. In such a case, the twice-larger scale contributes most to the stretching of smaller-scale vortices. This generation mechanism of small-scale vortices is similar to the one observed in fully developed turbulence in a periodic cube and consistent with the picture of the energy cascade. On the other hand, large-scale vortices, that is, vortices as large as the height, are stretched and amplified directly by the mean flow. We show quantitative evidence of these scale-dependent generation mechanisms of vortices on the basis of numerical analyses of the scale-dependent enstrophy production rate. We also demonstrate concrete examples of the generation process of the hierarchy of multiscale vortices.

Relative Efficiency of Ancillary and Small Scale Units

1978 ◽  
Vol 3 (4) ◽  
pp. 279-284
Author(s):  
K.R. Shaligram
Keyword(s):  
Small Firms ◽  
Large Scale ◽  
Small Scale ◽  
Underlying Assumption ◽  
Significant Difference ◽  
End Products ◽  
Policy Measures ◽  
The Mean ◽  
Small Manufacturers ◽  
Better Than

Ancillary units are small firms manufacturing and supplying intermediate goods, typically to large firms. Several policy measures are under consideration to raise the output of the ancillary industry to the level of 15 per cent of the value of output of the large scale industry by 1985. The underlying assumption appears to be that the ancillary status enhances the prospect for the viability of the small firm. This paper examines whether ancillary units perform better than small scale units (small manufacturers of end products) under the conditions prevailing in India. The findings reveal no significant difference in the mean performance of the two classes of small firms. It also draws implications for policymakers and management from the findings.

Field-aligned current ordering in ground and space measurements

2020 ◽  
Author(s):  
Malcolm Dunlop ◽  
Junying Yang ◽  
Xiangcheng Dong ◽  
Mervyn Freeman ◽  
Neil Rogers ◽  
...  
Keyword(s):  
Large Scale ◽  
Correlation Coefficients ◽  
Lower Latitude ◽  
Time Shift ◽  
Small Scale ◽  
Maximum Correlation ◽  
Substorm Activity ◽  
The Mean ◽  
Field Aligned Current ◽  
Statistical Trends

<p>The orientation of field-aligned current sheets (FACs) can be inferred from dual-spacecraft correlations of the FAC signatures between two Swarm spacecraft (A and C), using the maximum correlations obtained from sliding data segments. Statistical analysis of both the correlations and the inferred orientations shows clear trends in magnetic local time (MLT) which reveal behaviour of both large and small scale currents. The maximum correlation coefficients show distinct behaviour in terms of either the time shift, or the shift in longitude between Swarm A and C for various filtering levels. The lower-latitude FACs show the strongest correlations for a broad range of MLT centred on dawn and dusk, with a higher correlation coefficient on the dusk-side and lower correlations near noon and midnight, and broadly follow the mean shape of the auroral boundary for the lower latitudes corresponding to Region 2 FACs (and are most well-ordered on the dusk side). Individual events sampled by higher altitude spacecraft (e.g. the 4 Cluster spacecraft), in conjunction with Swarm (mapping both to region 1 and 2), also show two different domains of FACs: time variable, small-scale (10s km), and more stationary large-scale (>100 km) FACs. We investigate further how these FAC regimes are dependent on geomagnetic activity, focusing on high activity events. Both the statistical trends, and individual conjugate events, show comparable effects seen in the ground magnetometer signals (dH/dt) during storm/substorm activity and show distributions that are similar.</p>

The Use of Large Scale Parameters in Small Scale Diffusion Studies

1957 ◽  
Vol 38 (1.1) ◽  
pp. 6-12 ◽  
Author(s):  
William G. Tank
Keyword(s):  
Large Scale ◽  
Meteorological Parameters ◽  
Surface Wind ◽  
Small Scale ◽  
Relative Importance ◽  
Wind Vector ◽  
Scale Parameters ◽  
Diffusion Studies ◽  
The Mean ◽  
Low Levels

A method is set forth whereby gaseous diffusion in the low levels of the atmosphere can be calculated by Roberts' diffusion equation (modified to consider instantaneous volume sources) using only large scale synoptic parameters that are readily obtainable from the surface analysis and pibal reports. The three pertinent meteorological parameters utilized are: (1) the mean surface wind, (2) the angle between the surface wind vector and the surface isobars, and (3) the height of the gradient level. Theoretical and observed dosage values are compared by means of dosage isopleth diagrams. Results show that the method yields quite satisfactory results, with regard to both dosage magnitude and distribution. The assumptions necessary for the application of the method and its limitations are mentioned and their relative importance discussed.

Scaling Effect on Dynamic Impact Response of Structures in Fluid Fields

2013 ◽  
Author(s):  
Zhongheng Guo ◽  
Lingyu Sun ◽  
Taikun Wang ◽  
Junmin Du ◽  
Han Li ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Dimensional Analysis ◽  
Large Scale ◽  
Scaling Laws ◽  
Scaling Law ◽  
Fluid Pressure ◽  
Structural Safety ◽  
Scale Model ◽  
Small Scale ◽  
Water Tank

At the conceptual design phase of a large-scale underwater structure, a small-scale model in a water tank is often used for the experimental verification of kinematic principles and structural safety. However, a general scaling law for structure-fluid interaction (FSI) problems has not been established. In the present paper, the scaling laws for three typical FSI problems under the water, rigid body moves at a given kinematic equation or is driven by time-dependent fluids with given initial condition, as well as elastic-plastic body moves and then deforms subject to underwater impact loads, are investigated, respectively. First, the power laws for these three types of FSI problems were derived by dimensional analysis method. Then, the laws for the first two types were verified by numerical simulation. In addition, a multipurpose small-scale water sink test device was developed for numerical model updating. For the third type of problem, the dimensional analysis is no longer suitable due to its limitation on identifying the fluid pressure and structural stress, a simulation-based procedure for dynamics evaluation of large-scale structure was provided. The results show that, for some complex FSI problems, if small-scale prototype is tested safely, it doesn’t mean the full-scale product is also safe if both their pressure and stress are the main concerns, it needs further demonstration, at least by numerical simulation.

Scale-to-scale energy and enstrophy transport in two-dimensional Rayleigh–Taylor turbulence

2015 ◽  
Vol 786 ◽  
pp. 294-308 ◽  
Author(s):  
Quan Zhou ◽  
Yong-Xiang Huang ◽  
Zhi-Ming Lu ◽  
Yu-Lu Liu ◽  
Rui Ni
Keyword(s):  
Kinetic Energy ◽  
Thermal Energy ◽  
Scaling Laws ◽  
Isotropic Turbulence ◽  
Thermal Dissipation ◽  
Small Scale ◽  
Two Dimensional ◽  
Space Technique ◽  
Small Scales ◽  
The Mean

We apply a recently developed filtering approach, i.e. filter-space technique (FST), to study the scale-to-scale transport of kinetic energy, thermal energy, and enstrophy in two-dimensional (2D) Rayleigh–Taylor (RT) turbulence. Although the scaling laws of the energy cascades in 2D RT systems follow the Bolgiano–Obukhov (BO59) scenario due to buoyancy forces, the kinetic energy is still found to be, on average, dynamically transferred to large scales by an inverse cascade, while both the mean thermal energy and the mean enstrophy move towards small scales by forward cascades. In particular, there is a reasonably extended range over which the transfer rate of thermal energy is scale-independent and equals the corresponding thermal dissipation rate at different times. This range functions similarly to the inertial range for the kinetic energy in the homogeneous and isotropic turbulence. Our results further show that at small scales the fluctuations of the three instantaneous local fluxes are highly asymmetrically distributed and there is a strong correlation between any two fluxes. These small-scale features are signatures of the mixing and dissipation of fluids with steep temperature gradients at the fluid interfaces.

Nonlinear interactions in turbulence with strong irrotational straining

1997 ◽  
Vol 337 ◽  
pp. 333-364 ◽  
Author(s):  
N.K.-R. KEVLAHAN ◽  
J.C.R. HUNT
Keyword(s):  
Large Scale ◽  
Order Term ◽  
Initial Energy ◽  
Perturbation Series ◽  
Small Scale ◽  
Bluff Bodies ◽  
Leading Order ◽  
Viscous Effects ◽  
First Case ◽  
Maximum Amplification

The rate of growth of the nonlinear terms in the vorticity equation are analysed for a turbulent flow with r.m.s. velocity u0 and integral length scale L subjected to a strong uniform irrotational plane strain S, where (u0/L)/S=ε[Lt ]1. The rapid distortion theory (RDT) solution is the zeroth-order term of the perturbation series solution in terms of ε. We use the asymptotic form of the convolution integrals for the leading-order nonlinear terms when β= exp(−St)[Lt ]1 to determine at what time t and beyond what wavenumber k (normalized on L) the perturbation series in ε fails, and hence derive the following conditions for the validity of RDT in these flows. (a) The magnitude of the nonlinear terms of order ε depends sensitively on the amplitude of eddies with large length scales in the direction x2 of negative strain. (b) If the integral of the velocity component u2 is zero the leading-order nonlinear terms increase and decrease in the same way as the linear terms, even those that decrease exponentially. In this case RDT calculations of vorticity spectra become invalid at a time tNL∼L/u0k−3 independent of ε and the power law of the initial energy spectrum, but the calculation of the r.m.s. velocity components by RDT remains accurate until t= TNL∼L/u0, when the maximum amplification of r.m.s. vorticity is ω/S∼εexp(ε−1)[Gt ]1. (c) If this special condition does not apply, the leading-order nonlinear terms increase faster than the linear terms by a factor O(β−1). RDT calculations of the vorticity spectrum then fail at a shorter time tNL∼(1/S) ln(ε−1k−3); in this case TNL∼(1/S) ln(ε−1) and the maximum amplification of r.m.s. vorticity is ω/S∼1. (d) Viscous effects dominate when t[Gt ](1/S) ln(k−1(Re/ε)1/2). In the first case RDT fails immediately in this range, while in the second case RDT usually fails before viscosity becomes important. The general analytical result (a) is confirmed by numerical evaluation of the integrals for a particular form of eddy, while (a), (b), (c) are explained physically by considering the deformation of differently oriented vortex rings. The results are compared with small-scale turbulence approaching bluff bodies where ε[Lt ]1 and β[Lt ] 1.These results also explain dynamically why the intermediate eigenvector of the strain S aligns with the vorticity vector, why the greatest increase in enstrophy production occurs in regions where S has a positive intermediate eigenvalue; and why large-scale strain S of a small-scale vorticity can amplify the small-scale strain rates to a level greater than S – one of the essential characteristics of high-Reynolds-number turbulence.

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