Function Of Vertical Distribution Research Articles

Modeling dispersion of emissions from depressed roadways

This paper presents an analysis of data from a wind tunnel (Heist et al., 2009) conducted to study dispersion of emissions from three depressed roadway configurations; a 6 m deep depressed roadway with vertical sidewalls, a 6 m deep depressed roadway with 30° sloping sidewalls, and a 9 m deep depressed roadway with vertical sidewalls. The width of the road at the bottom of the depression is 36 m for all cases. All these configurations induce complex flow fields, increase turbulence levels, and decrease surface concentrations downwind of the depressed road compared to those of the at-grade configuration. The parameters of flat terrain dispersion models are modified to describe concentrations measured downwind of the depressed roadways. In the first part of the paper, a flat terrain model proposed by van Ulden (1978) is adapted. It turns out that this model with increased initial vertical dispersion and friction velocity is able to explain the observed concentration field. The results also suggest that the vertical concentration profiles of all cases under neutral conditions are best explained by a vertical distribution function with an exponent of 1.3. In the second part of the paper, these modifications are incorporated into a model based on the RLINE (Snyder et al., 2013) line-source dispersion model. While this model can be adapted to yield acceptable estimates of near-surface concentrations (z < 6 m) measured in the wind tunnel, the Gaussian vertical distribution in RLINE, with an exponent of 2, cannot describe the concentration at higher elevations. Our findings suggest a simple method to account for depressed highways in models such as RLINE and AERMOD through two parameters that modify vertical plume spread.

Concentration distribution of environmental dispersion in a wetland flow: Extended solution

Hydrological processes of contaminant transport in wetland flows are characterized by environmental dispersion. For concentration distribution of scalar dispersion, the preliminary estimate of vertical distribution (Wu et al., 2015) on small time scale is rigorously extended to account for high order effects as skewness and kurtosis. Based on a combination of Aris’ method of concentration moments and Gill’s generalized dispersion model, up to fourth order terms of vertical distribution functions and full-time two-dimensional concentration distribution are derived. The increments of damping factor, mainly representing the density of vegetation in wetlands, is shown to strengthen the mean distribution asymmetry and reduce the longitudinal dispersivity (with respect to skewness and kurtosis), and to increase the non-uniformity of vertical distribution. Therefore, dense vegetation corresponding to a large damping factor will postpone the time when Taylor’s dispersion model holds, and the first order approximation becomes rough on small time scale, demanding higher order modifications. The results provide more detailed and more accurate analytical solution for the typical environmental dispersion in wetland flows.

Warm-season thunderstorm development as a function of vertical distribution of relative humidity in the Lower Rio Grande Valley of Texas

Warm-season thunderstorm development as a function of vertical distribution of relative humidity in the Lower Rio Grande Valley of Texas

An approach to soil carbon accounting and mapping using vertical distribution functions for known soil types

Estimation and mapping of soil organic carbon storage in three dimensions for large areas is increasingly in demand for climate change reporting, but such estimates at large spatial scales and different soil depths are generally time consuming and expensive. This paper investigates the potential to reduce the number of required soil observations to one point close to the soil surface by applying negative exponential vertical depth functions of soil carbon distribution. This approach assumes that the carbon content at a depth of 1m, under relatively stable vegetation conditions, can be functionally related to the concentration at the soil surface in the absence of major recent disturbances (e.g. landslides, soil stock piling, etc.). Vertical distribution functions were developed for 38 soil profiles in the Midlands area of KwaZulu-Natal, South Africa, and normalized using the value observed close to the surface, followed by the grouping of soils with similar vertical distribution patterns. Normalization reduced the number of model parameters and enabled the multiplication of the exponential decline curve characteristics with a soil carbon stock value observed at the surface to represent an adequately represented value of soil carbon distribution to 1m at that observation point. The integral of the exponential function was used to calculate the soil carbon storage and raster layers were developed for each of the parameters in the integral to map soil carbon storage to 1m. The exponential decline function adequately fits the soil carbon data and is shown to relate to soil type. The resultant maps predicted soil organic carbon stocks to 1m in forest plantations and grasslands to vary from 19 to 46km·m−2.

Vertical Distribution of Structural Components in Corn Stover

In the United States, corn (Zea mays L.) stover has been targeted for second generation fuel production and other bio-products. Our objective was to characterize sugar and structural composition as a function of vertical distribution of corn stover (leaves and stalk) that was sampled at physiological maturity and about three weeks later from multiple USA locations. A small subset of samples was assessed for thermochemical composition. Concentrations of lignin, glucan, and xylan were about 10% greater at grain harvest than at physiological maturity, but harvestable biomass was about 25% less due to stalk breakage. Gross heating density above the ear averaged 16.3 ± 0.40 MJ kg−1, but with an alkalinity measure of 0.83 g MJ−1, slagging is likely to occur during gasification. Assuming a stover harvest height of 10 cm, the estimated ethanol yield would be &gt;2500 L ha−1, but it would be only 1000 L ha−1 if stover harvest was restricted to the material from above the primary ear. Vertical composition of corn stover is relatively uniform; thus, decision on cutting height may be driven by agronomic, economic and environmental considerations.

On Dispersion Property of Mild Slope Equation

A performance index is defined for linear wave dispersion property. The index measures the capability of a water wave model to simulate irregular wave transformation over general topography.Optimization of this index leads to:(1) the optimum vertical distribution functions for the nonlinear mild slope equations given by Isobe (1994) for different number of vertical distribution functions,(2) the optimum values of wave numbers to be used for the fully dispersive nonlinear wave model given by Nadaoka et al. (1994) for different number of vertical distribution functions,(3) the optimum values of the wave number to be used for the time dependent mild slope equation given by Kirby (1984). All optimized parameters are given as functions of the dimensionless peak frequency of the energy spectrum. Comparisons among the optimized models are given.

Experimental evaluation of depth-dependent lateral standard deviation for various ions in a-Si from one-dimensional tilted implantation profiles

This paper presents an experimental evaluation of the lateral standard deviation for various ions implanted in amorphous silicon (a-Si) with a simple extraction method using no complicated structures. First, we derive a model for the tilted implantation profile as a function of both tilt angle and lateral standard deviation, assuming a Gaussian lateral distribution function. This model is based on the assumption that two-dimensional (2-D) ion implantation profiles can be constructed from lateral and vertical distribution functions which are independent of each other, and it enables us to extract lateral standard deviation by only evaluating one-dimensional (1-D) (vertical) impurity profiles. Next, we systematically measure the ion implantation depth profiles at various tilts (0-60/spl deg/) with high resolution using secondary ion mass spectrometry (SIMS) and apply our proposed model for arsenic (As), phosphorus (P), antimony (Sb), and boron (B) ion implantations in a-Si over a wide energy range (20-160 keV) with a fixed dose of 1/spl times/10/sup 14/ cm/sup -2/. We successfully estimated not only average lateral standard deviation but also its depth dependence. Despite the simplicity of the model, the extracted depth-dependent lateral standard deviation shows good agreement over a wide energy range with the reported data calculated by theory or simulations. It is also shown that the lateral standard deviation has a linear depth dependence, and the lateral spread increases with the increase of depth for As, P, and Sb; on the other hand, it decreases for B, which reflects the difference of atomic mass between the incident ions and the target atoms.

Analysis of Dispersion and Shoaling Characteristics of Linearized Mild-Slope Equations

In this paper, the linearized form of the nonlinear mild-slope equations derived by Isobe (1994) is considered and analyzed for the dispersion, group velocity and shoaling characteristics. It is found that the dispersion relation is just a Padé's expansion of that obtained by the small amplitude wave theory. The agreement of the dispersion relation, group velocity and gradient of shoaling coefficient with the small amplitude wave theory is good from shallow to deep water even with small numbers of terms of the series in the mild-slope equations. The dispersion relation is also examined for evanescent waves. Furthermore, the vertical distribution functions for progressive and evanescent waves are analyzed and compared with the small amplitude wave theory. Then, the water depth limitation corresponding to the number of terms in the even-order polynomial vertical distribution functions is suggested.

The structure of upper level pelagic food webs in the Antarctic: Effect of phytoplankton distribution

We investigated diet composition and diversity and the diet overlap between species within the seabird community of the Scotia-Weddell Confluence region, Antarctica, during spring, autumn and winter. Seasonal changes in diet characteristics and overlap among species were viewed in the context of changes in prey availability as a function of vertical distribution in the water column. The latter was in turn affected by where phytoplankton and associated grazers were located. When primary productivity was confined to the pack ice during winter, thus bringing grazers and their predators closer to the surface, micronekton were much more vulnerable to avian predators and the latter were able to select prey on the basis of energetic value. As a consequence the upper food web was much less diffuse than during the other seasons when prey occurred throughout the upper portion of the water column and predators had to be opportunistic. The mobility of micronekton and nekton bring some structure to the upper portion of marine food webs, thereby introducing seasonal variability of trophic relationships within Antarctic food webs.

On the interactions between large-scale structure and finegrained turbulence in a free shear flow II. The development of spatial interactions in the mean

Organized structures in turbulent shear flow have been observed both in the laboratory and in the atmosphere and ocean. Recent work on modelling such structures in a temporally developing, horizontally homogeneous turbulent free shear layer (Liu &amp; Merkine 19766) has been extended to the spatially developing mixing layer, there being no available rational transformation between the two nonlinear problems. We consider the kinetic energy development of the mean flow, large-scale structure and finegrained turbulence with a conditional average, supplementing the usual time average, to separate the non-random from the random part of the fluctuations. The integrated form of the energy equations and the accompanying shape assumptions are used to derive ‘ amplitude ’ equations for the mean flow, characterized by the shear layer thickness, the non-random and the random components of flow (which are characterized by their respective energy densities). The closure problem was overcome by the shape assumptions which entered into the interaction integrals: the instability-wavelike large-scale structure was taken to be two-dimensional and the local vertical distribution function was obtained by solving the Rayleigh equation for various local frequencies; the vertical shape of the mean stresses of the fine-grained turbulence was estimated by making use of experimental results; the vertical shapes of the wave-induced stresses were calculated locally from their corresponding equations.

On the dynamics of monsoon disturbances

The dynamics of the disturbances due to the instabilities of horizontally and vertically shearing mean monsoon flow have been studied. The necessary conditions for internal jet instability are satisfied, and a barotropic-baroclinic instability analysis of the observed zonal flow has shown that the fastest growing modes are mainly due to the barotropic instability of the upper level flow. The amplitude of the most unstable mode is confined to the barotropically unstable upper tropospheric levels and the primary energy ccnversion is from the zonal kinetic energy to the eddy kinetic energy. This may explain the occurrence of observed westward moving waves at 200 mb. In an attempt to explain the formation of the monsoon depressions, the role of the CISK mechanism in conjunction with barotropic-barcclinic instability has teen explored. Instability analysis of vertically shearing zonal flows with prescribed vertical distribution functions for cumulus heating has shown that the horizontal scale, phase speed and structure, of the most unstable made depends upon the choice of the vertical heating distribution function. The horizontal scale of the most unstable made is larger for those distribution functions that provide heating to the larger vertical depths of the atmosphere. Instability analysis with the quasi-equilibrium assumption (QEA) of Arakawa and Schubert for parameterization of moist convection has shown that in a quiescent atmosphere the growth rate is a maximum for a perturbation of intermediate scale. The vertically integrated net heating is a maximum for the fastest growing mode. It has been shown that a two-layer model is not adequate for study of CISK with QFA parameterization of moist convection. For a two-layer model, the growth rates are infinite for the perturbations whose horizontal scales are proportional to the Rossby radius of deformation. In the presence of vertical shear, the cloud mass flux, as determined by QEA, becomes inversely proportional to the wavelength of the perturbation and the maximum growth rate occurs for the smallest scales. A combined CISK-barotropic-baroclinic instability analysis of the observed monsoon flow has been performed using the quasi-equilibrium assumption for the parameterization of moist convection. The structure and energetics of the computed linear perturbations are in good agreement with the structure and energetics of the observed monsoon depressions. The results of this study suggest that CISK may provide the primary driving mechanism for the growth of monsoon depressions.