Roughness Length Research Articles

Effect of thiol adsorption on the electrical resistance of copper ultrathin films

The impact of thiol adsorption on thin copper films, covered with a copper oxide layer, was investigated using electrical resistance measurements at various stages: during film growth, aging, exposure to air, and immersion in thiol solutions. Thin copper films (20 nm) were thermally evaporated, with variations in substrate temperature (RT, 330 and 390 K). Films deposited at 330 K exhibited the smallest percolation thickness and aging rates due to their compact morphology, showcasing lower surface roughness and correlation length. Exposure to air led to the formation of a Cu2O layer on the film surface. Subsequent immersion in a dodecanethiol solution in ethanol resulted in a resistance increase, ranging from 0.1 % to 0.4 %. This change was dependent on the substrate temperature, with the largest difference observed at 330 K. This observation suggests that samples grown at this temperature exhibited the highest electron-surface scattering. Moreover, by depositing a chromium surfactant layer, the impact of this scattering mechanism was amplified, leading to a resistance increase of up to 1.2 %. Mayadas-Shatzkes theory provided a good description of these resistance changes. The negatively charged S-head of the adsorbed thiols alters the electric field experienced by conduction electrons in the Cu2O/Cu interface, modifying the electron-surface scattering.

Variation in Zero Plane Displacement and Roughness Length for Momentum Revisited

Zero plane displacement height (d0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d_0$$\\end{document}) and momentum roughness length (z0m\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z_{0m}$$\\end{document}), describe the aerodynamic characteristics of a vegetated surface. Usually, d0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d_0$$\\end{document} and z0m\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z_{0m}$$\\end{document} are assumed to be constant functions of the physical characteristics of the surface. Prior evidence collected from the literature and our examination of flux tower data show that d0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d_0$$\\end{document} and z0m\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z_{0m}$$\\end{document} vary in time at sites with tree and shrub canopies, but not grasslands. The conventional explanations of these variations are based on linear functions of wind velocity and friction velocity, with little theoretical basis. This study explains the variation in aerodynamic parameters by matching four analytical canopy velocity models to a logarithmic above-canopy velocity profile at canopy height. d0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d_0$$\\end{document} and z0m\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z_{0m}$$\\end{document} come out as functions of 2 non-dimensional terms, the canopy momentum absorption capacity (parameter) and a (measurable) Péclet number. To test the theories of variation, we analysed the velocity profiles from Ozflux and Ameriflux sites. None of the theories could recreate d0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d_0$$\\end{document} and z0m\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z_{0m}$$\\end{document} at half-hourly intervals. However, the canopy velocity models were able better to recreate the distribution of the variations in d0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d_0$$\\end{document} and z0m\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z_{0m}$$\\end{document}. Additionally, the estimates of canopy momentum absorption capacity varied consistently with phenological changes in the canopies, whereas, the fitting parameters of the linear regression of using wind speed and friction velocity did not exhibit physically interpretable variations. The canopy velocity models may offer better predictions with an accurate estimation of the canopy height, a horizontally homogeneous and rigid canopy, and incorporation of the roughness sublayer.

Standardization of Dual-Doppler Radar–Derived Wind Fields during a Hurricane Landfall

Abstract A new methodology for standardizing radar-derived elevated dual-Doppler (DD)-synthesized wind maps to the near surface is presented, leveraging the spatial variability found within the horizontal wind speed fields. The methodology is applied to a dataset collected by Texas Tech University (TTU) using two TTUKa-band mobile radar systems during the landfall of Hurricane Delta (2020) in coastal Louisiana. Relevant portions of the DD wind fields are extracted from multiple heights between 100 and 400 m above ground level, combined into 10-min segments and standardized to a reference height of 10 m and an open exposure roughness length of 0.03 m. Extractions from these standardized wind fields are compared and validated against the standardized wind measurements from a micronet of seven TTU StickNet platforms providing “ground truth” within the DD analysis domain. The validation efforts confirm the developed DD wind field standardization methodology yields robust results with correlation coefficients greater than 0.88 and mean biases less than 1%. The results of this study provide a new means for incorporating elevated DD radar data into new and existing surface wind field analysis systems geared toward generating a wind field of record during a hurricane landfall. Significance Statement This work presents a new methodology for using radar-generated wind fields during a hurricane landfall to support the construction of a surface wind field analysis. Because radar-based wind measurements are inherently elevated above the surface and because the wind conditions well above the ground do not directly translate to the wind conditions experienced at the ground, a method for standardizing the elevated radar wind fields to the surface provides tremendous value to generating a spatially continuous wind field of record during a hurricane landfall event to better inform event response and recovery efforts. In addition, the need for detailed wind fields of record from landfalling hurricanes that approach structural design limits is critical as a single design-level storm can alter building code return period analysis. Detailed wind fields for these high-impact events can directly inform associated updates in building codes ultimately contributing to a more resilient built environment.

Turbulent flow over aligned cylindrical obstacles

Turbulent flow and boundary-layer (BL) characteristics over cylindrical obstacles have been understudied compared to the flow dynamics around cubic roughness in the urban BL literature. Using large-eddy simulation, we investigate a turbulent BL flow developed over two vertically oriented cylindrical obstacles aligned downstream. For widely separated cylinders, the wake flow undergoes periodic oscillations akin to vortex shedding behind an isolated cylinder. As the height-to-width aspect ratio (AR) of the canyon bounded by the cylinders increases, the streamline geometry exhibits a clear transition from isolated to wake interference and skimming regimes. Two-point autocorrelation functions of velocities confirm a strong coupling of canyon flow with the roughness sublayer for wider canyons, while with evident decoupling as the canyon narrows. The length scales, which measure the spatial correlation in the flow, decrease in both lateral and vertical directions with increasing AR. Turbulent kinetic energy and momentum fluxes below the roughness sublayer present pronounced monotonic scaling with AR (with R-squared values up to 0.84 and 0.98, respectively), resulting in a consistent variation in the surface roughness aerodynamic parameters, the roughness length (z0) and zero-plane displacement (d), with AR. Quantitative differences in the results with respect to those well-established for street canyons are analyzed, with the similarities highlighted. The results offer insights into boundary-layer flow parameterization concerning cylinder-occupied surface roughness.

Study on Morphometrical Urban Aerodynamic Roughness Multi-Scale Exploration Using LiDAR Remote Sensing

This study proposes the use of light detection and ranging (LiDAR) remote sensing (RS) to support morphometric research for estimating the aerodynamic roughness length (z0 ) of building placement on various scales. A LiDAR three-dimensional point cloud (3DPC) data processing graphical user interface (GUI) was developed to explore the z0 and related urban canopy parameters (UCPs) in the Incheon metropolitan area in South Korea. The results show that multi-scale urban aerodynamic roughness exploration is viable and can address differences in urban building data at various spatial resolutions. Although validating morphological multi-scale UCPs using dense tall towers is challenging, emerging low-cost and efficient methods can serve as substitutes. However, further efforts are required to link the measured z0 to building form regulations, such as floor area ratio, and expand RS research to obtain more quantitative and qualitative knowledge.

A Comparative Study on Wind Profiles and Surface Aerodynamic Parameters of Typhoons Over Coastland and Coastal Sea

AbstractUnderstanding the aerodynamic characteristics of landfalling typhoons is of great importance for both wind engineering and meteorology. This study comparatively investigated the near‐surface wind profiles and aerodynamic parameters over coastland and coastal sea areas using typhoon observational data collected by Doppler wind lidars and wind tower anemometers during the passage of 15 typhoons that made landfall over China during 2009–2020. Specifically, the three surface aerodynamic parameters of roughness length, friction velocity, and drag coefficient (Cd) were obtained using the logarithmic law wind profile method. Results showed that the near‐surface wind profiles became much closer to the power law wind profile with increase in wind speed. The values of roughness length and friction velocity over the coastal sea were found to exceed those over coastland areas when the 10‐m wind speed (U(10)) was larger than 18 m s−1. The critical wind speed at which Cd peaks over the coastal sea was found to be 24 m s−1. There are two peaks in the variation of Cd with U(10) under the condition of onshore wind over the sea, which has never been reported in previous observational studies. Finally, a formula for Cd was proposed to describe the variation in Cd with U(10) under the condition of onshore wind over land, which is expected to be applied in the typhoon surface layer scheme to improve numerical simulation of landfalling typhoons.

Momentum transfer and foam production via breaking waves in hurricane conditions

Generated under hurricane conditions, a slip layer composed of foam, spray, bubble emulsion, etc. determines the behavior of surface drag with wind speed. This study estimates foam's contribution to this behavior. A logarithmic parametrization of surface drag is introduced, where the effective roughness length of the underlying surface is decomposed into three fractional roughness lengths. These correspond to the foam-free area (as determined by open-ocean data at low wind speeds and laboratory data at high wind speeds), which includes the effects of spray, bubble emulsion, etc., and ocean areas covered by whitecaps and streaks, each weighted by their respective coverage coefficients. A key concept of this approach is the use of well-established experimental bubble-size spectra produced by breaking surface waves to obtain the foam-produced effective roughness length. This method provides a fair correlation of the logarithmic parametrization of surface drag against wind speed with a wide class of experimental data. Additionally, this approach estimates the hurricane's potential intensity, demonstrating reasonable agreement with experimental findings.

An Improved Non‐Local Planetary Boundary Layer Parameterization Scheme in Weather Forecasting and Research Model Based on a 1.5‐Order Turbulence Closure Model

AbstractPlanetary boundary layer (PBL) modeling is a primary contributor to uncertainties in a numerical weather prediction (NWP) model due to difficulties in modeling the turbulent transport of surface fluxes. The Weather Research and Forecasting model (WRF) has provided many PBL schemes that may feature a non‐local transport component driven by large eddies or a one‐and‐half order turbulence closure model, but few of them possess the two features at once. In the present study, a turbulent kinetic energy (TKE)‐based eddy diffusivity/viscosity method is integrated into the non‐local Asymmetric Convective Model version 2 (ACM2) PBL scheme and implemented in WRF. The original first‐order eddy‐diffusivity term in ACM2 is discarded and an extra prognostic equation for TKE, which considers the tendency of TKE by buoyancy, wind shear, vertical transport, and dissipative processes, is supplied to calculate the diffusivity/viscosity. Non‐local transport is modeled the same as ACM2 using the transilient matrix method. Idealized tests using prescribed surface heat flux and roughness length are performed. TKE‐ACM2 displays advantages over the PBL scheme developed by Bougeault and Lacarrère (hereinafter referred to as Boulac) and ACM2 in the wind speeds (WS) profile because it better matches large‐eddy simulations results in the surface momentum flux. Real case simulations show that TKE‐ACM2 generally outperforms in the diurnal vertical profiles of WS under stable conditions. TKE‐ACM2 also produces a better alignment under moderately unstable conditions in the early nighttime at the urban LiDAR station. However, the model exhibits discrepancies more apparently under a more unstable condition during the winter daytime.

Rethinking the Roughness Height: An Improved Description of Temperature Profiles over Short Vegetation

In this study, we present an extension to the Monin–Obukov similarity theory (MOST) for the roughness sublayer (RSL) over short vegetation. We test our theory using temperature measurements from fiber optic cables in an array-shaped set-up. This provides a high vertical measurement resolution that enables us to measure the sharp temperature gradients near the surface. It is well-known that MOST is invalid in the RSL as the flow is distorted by roughness elements. However, to derive the surface temperature, it is common practice to extrapolate the logarithmic profiles down to the surface through the RSL. Instead of logarithmic behaviour defined by MOST near the surface, our observations show near-linear temperature profiles. This log-to-linear transition is described over an aerodynamically smooth surface by the Van Driest equation in classical turbulence literature. Here we propose that the Van Driest equation can also be used to describe this transition over a rough surface, by replacing the viscous length scale with a surface length scale Ls\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$L_s$$\\end{document} that represents the size of the smallest eddies near the grass structures. We show that Ls\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$L_s$$\\end{document} scales with the geometry of the vegetation and that the model shows the potential to be scaled up to tall canopies. The adapted Van Driest model outperforms the roughness length concept in describing the temperature profiles near the surface and predicting the surface temperature.

The Wind‐Blown Sand Experiment in the Empty Quarter Desert: Roughness Length and Saltation Characteristics

AbstractThe Empty Quarter Desert, one of Earth's major dust sources, frequently experiences dust storms due to wind erosion. Despite its significance as a primary dust source on a global scale, in‐situ observations from this region had not been reported until very recently. In summer 2022, the WInd‐blown Sand Experiment (WISE) Phase‐1 was initiated in the Empty Quarter Desert of the United Arab Emirates, and continued until 7 February 2023. Utilizing a diverse array of instruments, we measured winds, temperature, humidity, radiation fluxes, saltation, and the physical and optical properties of dust aerosols, atmospheric electric fields, and soil characteristics. A total of 38 distinct sand‐saltation events were recorded from September 2022 to February 2023, with activity peaking between 13:00 and 14:00 local time. Key findings include the identification of dominant wind patterns, and the measurement of the average aerodynamic roughness length (z0) at 0.8 ± 0.6 mm, and the thermal roughness length (zh) at 0.3 ± 0.5 mm—the first estimation of zh for this area. In‐situ observations revealed that dust particle concentrations near the surface increased 1.7‐fold on days with saltation compared to days without it. Moreover, we determined a wind‐speed threshold for initiating saltation at 7.70 m s−1. This comprehensive data set significantly advances our understanding of atmospheric‐soil interactions and sand movement dynamics, providing invaluable insights for ongoing research into desert environments and the global dust cycle.

Elastic-plastic collision mechanism of micron-sized particle impacting rough surfaces

The interaction between micron-sized particles and rough surfaces represents a common natural phenomenon. Diverse Gaussian rough surfaces are reconstructed by utilizing inverse Fourier transformation, and the impact of surface roughness on the collision of micron-sized particles is investigated, scrutinized through the sizes of RMS roughness and correlation length from 0.025 μm to 0.2 μm. Given the relevance of surface roughness to particle size, it focuses on 1 μm particles collision—a dimension representative size ingested in the turbine blade cooling passage. The results indicate that RMS roughness primarily influences the height of asperities, whereas correlation length predominantly affects the density of asperities. COR diminishes with increasing roughness, and does not exhibit a decline with escalating speed, when the correlation length is small. The maximum contact area remains relatively constant with the larger roughness. Rotational velocity and rebound angle are predominantly impacted by the RMS roughness, less influence of the correlation length.

The application of a high-density street-level air temperature observation network (HiSAN): Spatial and temporal variations of thermal and wind condition in different climatic condition types

Different patterns of urban development will result in different characteristics of the urban heat island effect (UHI). In order to explore the impacts of urban environment characteristics, wind conditions, and climatic condition types on UHI over different periods, this study adopted Tainan City as the study site, and utilized the surface roughness length and wind prediction, to evaluate the correlation between wind conditions and UHI, as well as the thermal environment affected by different environmental. The UHI characteristics were evaluated by using 100 measurement stations (HiSAN) located in different urban environments. The results revealed the expansion of the daily temperature range was associated with an increase in the eastwest UHI centroid point movement; wind conditions affected north-south shifts of UHI centroid point. The built environments was positively correlate with daytime (0.24) and nighttime (0.68) temperatures. Daytime water bodies notably cool surroundings (correlation -0.52), and green spaces enhance nighttime cooling (correlation -0.64). Wind speed negatively correlates with UHI deviation values during the daytime (-0.17) and nighttime (-0.58). The study highlights the impact of wind speeds and temperature ranges on UHI movement, emphasizing effective ventilation's role in urban cooling and quantifying the importance of water and green space in mitigating UHI.

The role of nanosize dependence of dislocation and surface roughness concentrations to calculate lattice thermal conductivity in In0.53Ga0.47As nanofilms

ABSTRACT Systematic empirical relations were established for the nanosize-dependent surface roughness, ϵ ( D ) , dislocations, N D ( D ) , and effective length to examine their effects on the temperature-dependent lattice thermal conductivity (LTC) within the framework of the Morelli-Callaway model for In0.53Ga0.47As alloy films with thicknesses ranging from 10 to 70 and 1400 nm, the latter representing the material’s bulk state. The results were analyzed for film thicknesses of 2, 5, 200, and 500 nm, under the assumption that electrons and impurities are unaffected by nanosize, while a small alloy parameter significantly and sensitively alters the LTC curve in medium and high-temperature regions. According to these new findings, and considering phonon scattering processes, the LTC’s temperature dependence is sufficiently reduced at the nanoscale and fits well with the available reported experimental findings. It was also discovered that the LTC’s peak maximum value and its corresponding temperature are influenced by the film’s dislocation concentration, surface roughness, and thickness. Unravelling the complex interplay between nanosize-dependent dislocation and surface roughness concentrations becomes critical for a thorough knowledge when examining the delicate nuances of LTC in In0.53Ga0.47As nanofilms. Finally, the Morelli-Callaway-based model has been modified to calculate LTC for nanofilms without fitting parameters, provided their related bulk state values are known.

Investigating the impact of tropical deforestation on Indian monsoon hydro-climate: a novel study using a regional climate model

This study uses a state-of-the-art regional climate model (RCM) to examine how tropical deforestation affects the meteorology of the Indian Summer Monsoon (ISM). Incorporating insights from existing research on deforestation by climate scientists, alongside evidence of environmental deterioration in semi-arid, hilly and tropical regions of Southeast Asia, this research seeks to elucidate the critical influence of anthropogenic reasons of climate change on the hydroclimate of ISM. Employing “tropical deforestation” design experiments with the ICTP-RegCMv4.4.5.10 RCM the study evaluates the effects on meteorological parameters including precipitation, circulation patterns and surface parameters. This experimental design entails substituting vegetation type in the land use map of RegCMv4.4.5.10 model, such as deciduous and evergreen trees in Southeast Asia with “short grass” to mimic tropical deforestation. Findings reveal that deforestation induces abnormal anti-cyclonic circulation over eastern India curtails moisture advection, diminishing latent heat flux and moisture transport, leads to a decrease in precipitation compared to control experiment scenario. Alterations in albedo and vegetation roughness length attributable to deforestation impact temperature, humidity, precipitation, consequently exacerbating drought and heatwave occurrences. Additionally, the study also explores deforestation-induced feedback on ISM precipitation variability. The study concludes that deforestation substantially alters land-surface characteristics, water and energy cycle, and atmospheric circulation, thereby influencing regional climate dynamics. These findings offer foundational insights into comprehending land-use and land-cover changes and their implications for climate change adaptation strategies.

Physics schemes in the first version of NCEP operational hurricane analysis and forecast system (HAFS)

This document summarizes the physics schemes used in two configurations of the first version of the operational Hurricane Analysis and Forecast System (HAFSv1) at NOAA NCEP. The physics package in HAFSv1 is the same as that used in NCEP global forecast system (GFS) version 16 except for an additional microphysics scheme and modifications to sea surface roughness lengths, boundary layer scheme, and the entrainment rate in the deep convection scheme. Those modifications are specifically designed for improving the simulation of tropical cyclones (TCs). The two configurations of HAFSv1 mainly differ in the adopted microphysics schemes and TC-specific modifications in addition to model initialization. Experiments are made to highlight the impacts of TC-specific modifications and different microphysics schemes on HAFSv1 performance. Challenges and developmental plans of physics schemes for future versions of operational HAFS are discussed.

Ship Flow of the Ryuko-maru Calculated by the Reynolds Stress Model Using the Roughness Function at the Full Scale

The k-omega SST turbulence model is extensively employed in Reynolds-averaged Navier–Stokes (RANS)-based Computational Fluid Dynamics (CFD) calculations. However, the accuracy of the estimation of viscous resistance and companion flow distribution for full-sized vessels is not sufficient. This study conducted a computational analysis of the flow around the Ryuko-maru at model-scale and full-scale Reynolds numbers utilizing the Reynolds stress turbulence model (RSM). The obtained Reynolds stress distribution from the model-scale computation was compared against experimental measurements to assess the capability of the RSM. Furthermore, full-scale computations were performed, incorporating the influence of hull surface roughness, with the resulting wake distributions juxtaposed with the actual ship measurements. The full-scale calculation employed the sand-grain roughness function, and an optimal roughness length scale was determined by aligning the computed wake distribution with Ryuko-maru’s measured data. The results of this study will allow for the direct performance estimation of full-scale ships and contribute to the design technology of performance.

Using the Sensible Heat Flux Eddy Covariance-Based Exchange Coefficient to Calculate Latent Heat Flux from Moisture Mean Gradients Over Snow

In absence of the high-frequency measurements of wind components, sonic temperature and water vapour required by the eddy covariance (EC) method, Monin–Obukhov similarity theory (MOST) is often used to calculate heat fluxes. However, MOST requires assumptions of stability corrections and roughness lengths. In most environments and weather situations, roughness length and stability corrections have high uncertainty. Here, we revisit the modified Bowen-ratio method, which we call C-method, to calculate the latent heat flux over snow. In the absence of high-frequency water vapour measurements, we use sonic anemometer data, which have become much more standard. This method uses the exchange coefficient for sensible heat flux to estimate latent-heat flux. Theory predicts the two exchange coefficients to be equal and the method avoids assuming roughness lengths and stability corrections. We apply this method to two datasets from high mountain (Alps) and polar (Antarctica) environments and compare it with MOST and the three-layer model (3LM). We show that roughness length has a great impact on heat fluxes calculated using MOST and that different calculation methods over snow lead to very different results. Instead, the 3LM leads to good results, in part due to the fact that it avoids roughness length assumptions to calculate heat fluxes. The C-method presented performs overall better or comparable to established MOST with different stability corrections and provides results comparable to the direct EC method. An application of this method is provided for a new station installed in the Pamir mountains.

Effect of Annealing on Stress, Microstructure, and Interfaces of NiV/B4C Multilayers

The functionality and reliability of nanoscale multilayer devices and components are influenced by changes in stress and microstructure throughout fabrication, processing, and operation. NiV/B4C multilayers with a d-spacing of 3 nm were prepared by magnetron sputtering, and two groups of annealing experiments were performed. The stress, microstructure, and interface changes in NiV/B4C after annealing were investigated by grazing-incidence X-ray reflectometry (GIXR), grazing-incidence X-ray diffraction (GIXRD), X-ray diffuse scattering, and grazing-incidence small-angle X-ray scattering (GISAXS). The temperature dependence experiments revealed a gradual shift in the multilayer stress from compression to tension during annealing from 70 °C to 340 °C, with the stress approaching near-zero levels between 70 °C and 140 °C. The time-dependent experiments indicated that most of the stress changes occurred within the initial 10 min, which showed that prolonged annealing was unnecessary. Combining the X-ray diffraction and X-ray scattering measurements, it was found that the changes in the thickness, interface roughness, and lateral correlation length, primarily due to crystallization, drove the changes in stress and microstructure.

Evaluation of multi-layer urban canopy model (MLUCM) for urban microclimate predictions at different urban contexts

Modeling tools are often used to obtain a better understanding of the characteristics of urban microclimates. Among the different approaches to physics-based modeling, urban canopy models tend to be computationally faster than computational fluid dynamics (CFD) simulations. However, the evaluation of current urban canopy models for different urban characteristics is still limited, especially for wind speed. This study aims to evaluate the potential usability of the existing urban canopy model for microclimate variable prediction in different urban contexts, specifically the vertical city weather generator (VCWG) v1.4.5, which can predict microclimate variables at different vertical heights. The measurement data used in model evaluation were obtained from 248 weather stations in Seoul, Republic of Korea. The results showed that among the input parameters, a few variables had significant impact on the wind speed prediction results, namely, the turbulent coefficient during unstable conditions, the pressure gradient coefficient, and the aerodynamic roughness length. The discrepancy in wind-speed prediction tended to be lower during the summer season, with lower wind speeds at the rural weather station. Further investigations also addressed the significant parameters of wind speed prediction related to the calculation of the turbulent diffusion coefficient and pressure gradient.

Optimal design of series of pipes in sewer systems including pumping stations for flat terrains

ABSTRACT This paper proposes a methodology for the optimal design of series of sewer pipes including pumping stations. It employs a Shortest Path Algorithm to select the optimal combination of pipe diameters and invert elevations, as well as the optimal pumping features such as the number of pumps, location, and pumping head. The methodology is intended to be applied to the design of any sewer series. Although these are uncommon in real infrastructure, the study allows an analysis of the effect of pipe roughness, inflows, and pipe length on the total cost of the system and pumping features. The methodology was tested in theoretical series of 10 and 20 pipes as well as in a real series that is part of the sewer system of Bogotá, Colombia. The resulting designs suggested that using smooth pipes and reducing the pumping flow rate would decrease the cost of sewer systems in flat terrain.