scholarly journals Some Observations of Wind Velocity Autocorrelations in the Lowest Layers of the Atmosphere

1955 ◽  
Vol 8 (4) ◽  
pp. 535 ◽  
Author(s):  
RJ Taylor
Keyword(s):  
Viscous Dissipation ◽  
Wind Velocity ◽  
Fair Agreement ◽  
Inertial Subrange ◽  
Time Interval ◽  
Mean Square ◽  
Shearing Stress ◽  
Local Isotropy ◽  
Dissipation Of Energy

From wind velocity observations in the lowest layers of the atmosphere, mean square velocity differences over a time interval at a point fixed in space are derived and their variation with the time interval is considered. The magnitude of these mean square differences is related to the rate of viscous dissipation of energy and to the shearing stress. On the average, fair agreement with predictions from the dimensional arguments of the theory of local isotropy is shown even though the results pertain to eddy sizes outside. the inertial subrange as usually defined.

Observations of Small-Scale Turbulence and Energy Dissipation Rates in the Cloudy Boundary Layer

2006 ◽  
Vol 63 (5) ◽  
pp. 1451-1466 ◽  
Author(s):  
Holger Siebert ◽  
Katrin Lehmann ◽  
Manfred Wendisch
Keyword(s):  
Boundary Layer ◽  
Energy Dissipation ◽  
Wind Velocity ◽  
Turbulence Theory ◽  
Horizontal Wind ◽  
Inertial Subrange ◽  
Intermittent Flow ◽  
Small Scale ◽  
Dissipation Rates ◽  
Wide Range

Abstract Tethered balloon–borne measurements with a resolution in the order of 10 cm in a cloudy boundary layer are presented. Two examples sampled under different conditions concerning the clouds' stage of life are discussed. The hypothesis tested here is that basic ideas of classical turbulence theory in boundary layer clouds are valid even to the decimeter scale. Power spectral densities S( f ) of air temperature, liquid water content, and wind velocity components show an inertial subrange behavior down to ≈20 cm. The mean energy dissipation rates are ∼10−3 m2 s−3 for both datasets. Estimated Taylor Reynolds numbers (Reλ) are ∼104, which indicates the turbulence is fully developed. The ratios between longitudinal and transversal S( f ) converge to a value close to 4/3, which is predicted by classical turbulence theory for local isotropic conditions. Probability density functions (PDFs) of wind velocity increments Δu are derived. The PDFs show significant deviations from a Gaussian distribution with longer tails typical for an intermittent flow. Local energy dissipation rates ɛτ are derived from subsequences with a duration of τ = 1 s. With a mean horizontal wind velocity of 8 m s−1, τ corresponds to a spatial scale of 8 m. The PDFs of ɛτ can be well approximated with a lognormal distribution that agrees with classical theory. Maximum values of ɛτ ≈ 10−1 m2 s−3 are found in the analyzed clouds. The consequences of this wide range of ɛτ values for particle–turbulence interaction are discussed.

scholarly journals Zircon U-Pb and Pyrite Re-Os Isotope Geochemistry of ‘Skarn-Type’ Fe-Cu Mineralization at the Shuikoushan Polymetallic Deposit, South China: Implications for an Early Cretaceous Mineralization Event in the Nanling Range

Minerals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 480
Author(s):  
Shengbin Li ◽  
Yonghua Cao ◽  
Zeyou Song ◽  
Dan Xiao
Keyword(s):  
Contact Zone ◽  
Early Cretaceous ◽  
South China ◽  
Isotope Geochemistry ◽  
Time Interval ◽  
Mean Square ◽  
Geochronological Data ◽  
Nanling Range ◽  
Calcite Veins ◽  
Os Isotope

The Shuikoushan deposit is an economic ‘skarn-type’ polymetallic Pb-Zn deposit in South China. The deposit is located at the southern margin of the Hengyang basin in the northern part of the Nanling Range. Recently, economic Fe-Cu mineralization that occurs spatially connected to skarns along the contact zone between the granodiorite and limestones was discovered in the lower part of this deposit. Detailed zircon U-Pb geochronological data indicate that the granodiorite was emplaced at 153.7 ± 0.58 Ma (Mean Square of Weighted Deviates (MSWD) = 2.4). However, the pyrite Re-Os isochron age reveals that Fe-Cu mineralization formed at 140 ± 11 Ma (MSWD) = 8.1), which post-dates the emplacement of the granodiorite, as well as the previously determined timing of Pb-Zn mineralization (157.8 ± 1.4 Ma) in this deposit. Considering that Fe-Cu mineralization was connected with the contact zone and also faults, and that sulfide minerals commonly occur together with quartz and calcite veins that crosscut skarns, we interpret this mineralization type as being related to injection of post-magmatic hydrothermal fluids. The timing of Fe-Cu mineralization (140 ± 11 Ma) is inconsistent with a long-held viewpoint that the time interval of 145 to 130 Ma (e.g., Early Cretaceous) in the Nanling Range is a period of magmatic quiescence with insignificant mineralization, the age of 140 Ma may represent a new mineralization event in the Nanling Range.

An investigation of wind structure in the trades: anegada 1953

1956 ◽  
Vol 249 (963) ◽  
pp. 179-234 ◽  
Keyword(s):  
Wind Velocity ◽  
Pressure Field ◽  
Surface Wind ◽  
Fair Agreement ◽  
Vertical Shear ◽  
Mean Stress ◽  
Mean Motion ◽  
Horizontal Pressure ◽  
The Mean ◽  
Made In

This paper describes an observational study of the mean and larger-scale turbulent structure of the wind in the lowest 1500 m of the North-East Trades. The observed motions are used both alone and in conjunction with the horizontal pressure field to deduce values of the vertical transport of momentum; the pattern of cumulus cloud convection is borne in mind throughout. Sections 1 and 2 provide a brief survey of the background to the expedition and of the simplified equations by which the observations are interpreted. Section 3 describes the site and observations in detail. 466 double-theodolite pilot-balloon soundings were made in the spring of 1953 from the small flat island of Anegada (18°N, 64° W). Soundings were made on 15 days over a 27-day period, balloons being released at intervals of 5 to 15 min. The balloons, rising at about 150 m/min, were observed every 20s for 9 min, to obtain the three components of the motion in 50 m layers over the lowest 1350 m. Special observations of pressure were made in a network of neighbouring islands. The derivation of component air velocities and of the horizontal pressure gradient as a function of height is described in §4. Difficulty was experienced in obtaining the pressure field with requisite accuracy. Surface observations of the weather in relation to the main aim of the study are discussed in §5. The mean angle between surface wind and isobar over the 15-day period was 13°, notably less than the climatological value of about 33°. Section 6 discusses the properties of the mean horizontal motion for the whole period of observation. The easterly component of wind velocity was greatest at 350 m, and the wind veered with height through 24° in the first 1350 m. There was also a veer of geostrophic wind in this layer of about 13° so that some down-gradient motion remained at the top of the layer. It is shown that the mean values of the local and advective components of acceleration were negligible compared with others terms in the momentum balance. Section 7 uses the wind profiles of §6 together with the mean horizontal pressure field to find the distribution of shearing stress with height, assuming that ageostrophic flow is balanced by internal friction. The mean stress in the direction of the surface wind varied from 0-41 dyn/cm2 at the surface to —0.37 dyn/cm 2 at 1300 m. The former provides a coefficient of surface stress, based on the anemometer windspeed, c = 1.5 x 10- 3 . The mean stress in the direction normal to the surface wind varied from zero (assumed) at the surface to 0.17 dyn/cm 2 at 200 m, and was small above 800 m, but internal consistency is only obtained by assuming the horizontal gradient of temperature near the surface to be appreciably greater than the climatological value for the general area. The stresses and related gradients of mean motion imply eddy viscosities of order 10 5 cm 2 / s throughout the layer. Section 8 discusses the vertical profiles of daily mean wind, which are variable from day to day. It was not possible to analyze the profiles to find shearing forces because of uncertainty in the acceleration terms, and in the pressure field. Section 9 is concerned with the analysis of fluctuations of wind at heights up to 1350 m, using averaging periods increasing from about 3 h up to the whole 27-day period. For none of these averaging periods was there equipartition of eddying energy in the three velocity components; w2 the vertical intensity, was one to two orders of magnitude lower than u2, the horizontal intensities, the difference being greater the longer the averaging periods. The covariances uv,uw were also evaluated for various heights and averaging periods, uw increased with averaging period and from their variation crude estimates are made of lag covariances which are equivalent to spectra. Values of uv for the larger components of the motion sampled were in fair agreement with those of early workers, uw and vw were in general less than uv and did not vary systematically with averaging period. The values for the smaller scale components of the motion sampled were in fair agreement with shearing stresses computed by the method of geostrophic departure (§7). The direction of the resultant of uw and vw agreed surprisingly well with the direction of the vertical shear vector of the mean wind velocity, the implied coefficient of eddy viscosity for the spectral range sampled again being about I0 5 cm 2/s over the whole range of height. An appendix considers the effect of the island, about 30 km 2 in area, on the oceanic Trades; the land was strongly heated by the sun and a particular pattern of convective cloud was usually set up. The associated field of mean vertical motion, of the order of 10 cm/s, and the disturbance of the field of horizontal mean motion have been partly evaluated. It is found that the velocities measured on the upwind shore were fairly representative of those over the open ocean, even though slow steady rising and sinking motions were detected.

scholarly journals Incorporating Graph Attention and Recurrent Architectures for City-Wide Taxi Demand Prediction

2019 ◽  
Vol 8 (9) ◽  
pp. 414 ◽  
Author(s):  
Ying Xu ◽  
Dongsheng Li
Keyword(s):  
State Of The Art ◽  
Sequence Data ◽  
Building Blocks ◽  
Time Interval ◽  
Mean Square ◽  
Key Factors ◽  
Demand Prediction ◽  
Traffic Efficiency ◽  
Temporal Correlations ◽  
Spatial Dependencies

Taxi demand prediction is one of the key factors in making online taxi hailing services more successful and more popular. Accurate taxi demand prediction can bring various advantages including, but not limited to, enhancing user experience, increasing taxi utilization, and optimizing traffic efficiency. However, the task is challenging because of complex spatial and temporal dependencies of taxi demand. In addition, relationships between non-adjacent regions are also critical for accurate taxi demand prediction, whereas they are largely ignored by existing approaches. To this end, we propose a novel graph and time-series learning model for city-wide taxi demand prediction in this paper. It has two main building blocks, the first one utilize a graph network with attention mechanism to effectively learn spatial dependencies of taxi demand in a broader perspective of the entire city, and the output at each time interval is then transferred to the second block. In the graph network, the edge is defined by an Origin–Destination relation to capture non-adjacent impacts. The second one uses a neural network which is adept with processing sequence data to capture the temporal correlations of city-wide taxi demand. Using a large, real-world dataset and three metrics, we conduct an extensive experimental study and find that our model outperforms state-of-the-art baselines by 9.3% in terms of the root-mean-square error.

scholarly journals Characteristics of the turbulence in the flow at a tidal stream power site

2013 ◽  
Vol 371 (1985) ◽  
pp. 20120196 ◽  
Author(s):  
I. A. Milne ◽  
R. N. Sharma ◽  
R. G. J. Flay ◽  
S. Bickerton
Keyword(s):  
Turbulence Intensity ◽  
Spring Tide ◽  
Maximum Flow ◽  
Large Degree ◽  
Tidal Energy ◽  
Inertial Subrange ◽  
Mean Flow ◽  
Local Isotropy ◽  
Spectral Models ◽  
Tidal Stream

This paper analyses a set of velocity time histories which were obtained at a fixed point in the bottom boundary layer of a tidal stream, 5 m from the seabed, and where the mean flow reached 2.5 m s −1 . Considering two complete tidal cycles near spring tide, the streamwise turbulence intensity during non-slack flow was found to be approximately 12–13%, varying slightly between flood and ebb tides. The ratio of the streamwise turbulence intensity to that of the transverse and vertical intensities is typically 1 : 0.75 : 0.56, respectively. Velocity autospectra computed near maximum flood tidal flow conditions exhibit an f −2/3 inertial subrange and conform reasonably well to atmospheric turbulence spectral models. Local isotropy is observed between the streamwise and transverse spectra at reduced frequencies of f >0.5. The streamwise integral time scales and length scales of turbulence at maximum flow are approximately 6 s and 11–14 m, respectively, and exhibit a relatively large degree of scatter. They are also typically much greater in magnitude than the transverse and vertical components. The findings are intended to increase the levels of confidence within the tidal energy industry of the characteristics of the higher frequency components of the onset flow, and subsequently lead to more realistic performance and loading predictions.

Second-order spectral local isotropy in turbulent scalar fields

1977 ◽  
Vol 80 (4) ◽  
pp. 609-615 ◽  
Author(s):  
C. W. Van Atta
Keyword(s):  
Low Frequency ◽  
Scalar Fields ◽  
Second Order ◽  
Turbulence Theory ◽  
Inertial Subrange ◽  
Spatial Gradient ◽  
Local Isotropy ◽  
Absolute Magnitudes ◽  
The Individual ◽  
Isotropic Theory

This work was motivated by recent experimental results on the spectra of fluctuating temperature gradients in a heated turbulent boundary layer obtained by Sreenivasan, Danh & Antonia. Standard techniques of turbulence theory are used herein to derive expressions relating the individual one-dimensional spectra of each of the three components of the spatial gradient ∂θ/∂xiin a locally isotropic turbulent scalar field. The results of the isotropic theory explain all of the new observed features of the temperature-gradient spectra. The spectra of ∂θ/∂yand ∂θ/∂zdecrease monotonically with increasing wavenumber, in contrast to the well-known behaviour of the spectrum of ∂θ/∂x, which reaches a maximum value at roughly one-tenth the Kolmogorov wavenumber. The spectra of ∂θ/∂yand ∂θ/∂zare relatively rich in low frequency energy and relatively poor in high frequency energy compared with the spectrum of ∂θ/∂x. The absolute magnitudes of the spectra of ∂θ/∂yand ∂θ/∂zcalculated from the spectrum of ∂θ/∂xusing the isotropic relations are in generally good agreement with the corresponding measured spectra for a large range of wavenumbers, indicating second-order spectral local isotropy of the fine-scale scalar structure for sufficiently large wavenumbers. The form of the spectra of ∂θ/∂yand ∂θ/∂zin the inertial subrange is derived analytically.

Distortion of sonic bangs by atmospheric turbulence

1969 ◽  
Vol 37 (3) ◽  
pp. 529-563 ◽  
Author(s):  
S. C. Crow
Keyword(s):  
Scattering Theory ◽  
Critical Time ◽  
Observation Point ◽  
Inertial Subrange ◽  
Pressure Jump ◽  
Mean Square ◽  
Pressure Perturbation ◽  
Surface Integral ◽  
First Order ◽  
The Mean

Recorded pressure signatures of supersonic aircraft often show intense, spiky perturbations superimposed on a basicN-shaped pattern. A first-order scattering theory, incorporating both inertial and thermal interactions, is developed to explain the spikes. Scattering from a weak shock is studied first. The solution of the scattering equation is derived as a sum of three terms: a phase shift corresponding to the singularity found by Lighthill; a small local compression or rarefaction; a surface integral over a paraboloid of dependence, whose focus is the observation point and whose directrix is the shock. The solution is found to degenerate at the shock into the result given by ray acoustics, and the surface integral is identified with the scattered waves that make up the spikes. The solution is generalized for arbitrary wave-forms by means of a superposition integral. Eddies in the Kolmogorov inertial subrange are found to be the main source of spikes, and Kolmogorov's similarity theory is used to show that, for almost all timestafter a sonic-bang shock passes an observation point, the mean-square pressure perturbation equals$(\Delta p)^2 (t_c/t)^{\frac{7}{6}}$, where Δpis the pressure jump across the shock andtcis a critical time predicted in terms of meteorological conditions. For an idealized model of the atmospheric boundary layer,tcis calculated to be about 1 ms, a figure consistent with the qualitative data currently available. The mean-square pressure perturbation just behind the shock itself is found to be finite but enormous, according to first-order scattering theory. It is conjectured that a second-order theory might explain the shock thickening that actually occurs.

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