Surface Layer Parameters Research Articles

Observed diurnal and intraseasonal variations in boundary layer winds over Ganges valley

The diurnal and intraseasonal variability in the surface winds are examined using high resolution measurements during the Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX) Phase III Integrated Ground based Experiment, conducted in the Ganges valley during 2014–15. The yearlong observations of lower boundary layer wind from the Ganges valley are discussed in this study. Wind speed and directions at the surface levels obtained from SOund Detection And Ranging (SODAR) and tower are compared and found, mostly SODAR measurements are consistent with tower during high wind conditions (greater than 4 ms−1) except under weak circumstances. Our analysis revealed that, the mean wind speed found to be a maximum (7.86 ms−1) during the monsoon season in the air layer between 10 m and 200 m level and shows a sharp increase near to the surface (at 20 m level). Analysis also depicts seasonal variations in wind speed are predominant in the lower boundary layer and it is closely linked to the large-scale flow patterns/disturbances. The turbulent kinetic energy (TKE) was found to be maximum at 165 m (0.62 m2s-2) during the pre-monsoon due to enhanced surface heating. The 93% and 75% of the wind speed profiles exhibited unstable conditions in the monsoon and post monsoon conditions. Moreover, the unstable layers are characterized by high wind speed and temperature structure function (CT2)in day time. On large scale, the wind speed gets strengthened (reduced) in the wet (dry) spell in the lower levels with distinct diurnal cycle in the Indo Gangetic Plain. The advection of moisture in the nocturnal periods in connection with the wet spells in the near surface level is observed and the wind speeds in the daytime (above 150 m) are also found to be stronger in the range 3.5–5 ms−1 in the dry spells due to the enhanced mixing. The diurnal cycle is more evident in the dry spells in the lower levels. Rainfall peak found in July 2014 is connected with the quasi-biweekly mode periodicity of 2–16 days and further, power spectrum analysis reveals that the presence of high frequency oscillations of periodicity less than 10 days and between 10 and 20 days in the surface layer parameters.

Impact of Mountainous Topography on Surface-Layer Parameters During Weak Mean-Flow Conditions

We investigate surface-layer characteristics over a mountainous ridge in the Central Himalayas, utilizing tower-based fast-response micrometeorological observations (at 12 and 27 m above ground level) for the winter months November 2013–January 2014. During this period, the site generally experienced clear skies and weak synoptic flow (wind speed < 2 m s−1), favouring a strong diurnal evolution of the atmospheric boundary layer. The observations show a regular change in wind direction from north-easterly during the night-time to westerly during the daytime throughout the season, indicating the systematic development of a mountain circulation due to changes in heating of the mountain slopes as the day advances. Considering the variations in wind direction and topography of the site, the tilt corrections are implemented sector-wise by segregating the data into three sectors, thus estimating three sets of coefficients for the tilt correction. Observations during fair-weather conditions (59 days only) are analyzed with the sensible heat flux (H) showing large diurnal variations, which are in-phase with the mean vertical velocity. The afternoon peak value of H is found to be ≈ 116 ± 80 W m−2. In contrast, diurnal variations of momentum flux and turbulent kinetic energy are less prominent with rather weak maxima occurring between 0900 and 1300 IST, the period when wind direction changes over the ridge. Variations of the dimensionless standard deviations of the vertical velocity component and temperature are found to scale with the stability parameter z/L under convective conditions, while taking into account the effect of self-correlation. The constancy of fluxes with height, slope-flow buoyancy and stress divergence are also analyzed to provide a rigorous evaluation of Monin–Obukhov similarity theory based on two-level turbulence measurements.

Multi-point Monin–Obukhov similarity in the convective atmospheric surface layer using matched asymptotic expansions

The multi-point Monin–Obukhov similarity (MMO) was recently proposed (Tong &amp; Nguyen, J. Atmos. Sci., vol. 72, 2015, pp. 4337–4348) to address the issue of incomplete similarity in the framework of the original Monin–Obukhov similarity theory (MOST). MMO hypothesizes the following: (1) The surface-layer turbulence, defined to consist of eddies that are entirely inside the surface layer, has complete similarity, which however can only be represented by multi-point statistics, requiring a horizontal characteristic length scale (absent in MOST). (2) The Obukhov length $L$ is also the characteristic horizontal length scale; therefore, all surface-layer multi-point statistics, non-dimensionalized using the surface-layer parameters, depend only on the height and separations between the points, non-dimensionalized using $L$. However, similar to MOST, MMO was also proposed as a hypothesis based on phenomenology. In this work we derive MMO analytically for the case of the horizontal Fourier transforms of the velocity and potential temperature fluctuations, which are equivalent to the two-point horizontal differences of these variables, using the spectral forms of the Navier–Stokes and the potential temperature equations. We show that, for the large-scale motions (wavenumber $k&lt;1/z$) in a convective surface layer, the solution is uniformly valid with respect to $z$ (i.e. as $z$ decreases from $z&gt;-L$ to $z&lt;-L$), where $z$ is the height from the surface. However, for $z&lt;-L$ the solution is not uniformly valid with respective to $k$ as it increases from $k&lt;-1/L$ to $k&gt;-1/L$, resulting in a singular perturbation problem, which we analyse using the method of matched asymptotic expansions. We show that (1) $-L$ is the characteristic horizontal length scale, and (2) the Fourier transforms satisfy MMO with the non-dimensional wavenumber $-kL$ as the independent similarity variable. Two scaling ranges, the convective range and the dynamic range, discovered for $z\ll -L$ in Tong &amp; Nguyen (2015) are obtained. We derive the leading-order spectral scaling exponents for the two scaling ranges and the corrections to the scaling ranges for finite ratios of the length scales. The analysis also reveals the dominant dynamics in each scaling range. The analytical derivations of the characteristic horizontal length scale ($L$) and the validity of MMO for the case of two-point horizontal separations provide strong support to MMO for general multi-point velocity and temperature differences.

Повышение качества поверхностного слоя и эксплуатационных свойств деталей электромеханической обработкой

A technological method for parts electro-mechanical treatment is considered. The investigation results of electro-mechanical treatment impact upon quality parameters of parts surface layer, physical-mechanical characteristics and operational properties are presented.

Definition of the Parameters of Surface Layer Based on Functionality of Parts

The problem of increased reliability of parts is solved in the direction of obtaining the characteristics of their surface layer, providing the highest possible wear resistance. Tolerances on the accuracy of the machine, set on the basis of its functionality, are divided into tolerances for the manufacture of the machine and wear tolerances. In order to increase the reliability of products, they strive for the greatest possible tolerance for wear, increasing the accuracy of parts manufacturing. As a result, the costs of manufacturing the machine unnecessarily increase. The dependence of the rate of wear of parts on the roughness and hardness of their surfaces is extreme; therefore, the task of determining the parameters of the surface layer of the parts is optimization. The use of the wear rate of rubbing surfaces is justified as an optimization criterion. The technique and algorithm for assigning the parameters of the surface layer, providing a minimum rate of wear of the mating surfaces are presented. To solve this problem, a random search method was used. A method for calculating the tolerances for the manufacture and wear of mated parts operating under friction conditions is proposed.

Evaluation of Physical Parameters of the Surface Layers Materials after Processing with the Use of Acoustic Wave

In this work an algorithm is proposed for estimating the physical parameters of surface layers of materials subjected to processing. The task of analyzing the state of materials is a modern and relevant material science task. At the present time, metal, ceramic, dielectric materials for various purposes have become widespread. Depending on the state of their sub-surface layers, their operational characteristics change. These characteristics are to some extent determined by external influences, especially mechanical. That is why, there is a problem of physical parameters estimation, which can be solved by innovative methods, for example, using acoustic waves. The paper presents the results of the development of new methods of research materials – methods of acoustic spectroscopy of flaw and study with their help the physical parameters of the subsurface layers.

Modelling sound propagation from a wind turbine under various atmospheric conditions

Sound propagation from a wind turbine is investigated with the help of coupled atmospheric and acoustical simulation. Eight instants of time during nine diurnal cycles of idealized large-scale cases result in 72 meteorological situations for which the boundary-layer profiles of wind and temperature, the downstream wake flow of the rotor, and the sound propagation from the wind turbine into upwind and downwind direction were calculated. The resulting sound levels are evaluated relative to a non-refractive atmosphere to focus on the impact of meteorologically induced refraction. Within a range of 1 km from the turbine the sound levels vary stronger in upwind direction than in downwind direction, and the varying background wind speed at hub level causes a higher variability of the relative sound levels than the variations of the surface-layer stability. Surface-layer parameters turn out to be of only limited suitability for a meteorological classification of the wind-turbine noise impact.

Теория и практика технологического обеспечения усталостной прочности деталей машин

On a basis of the theory of metal plastic deformation there are determined analytical ties between speed, power and temperature factors of machining with parameters of machinery surface layers defining their resistance to fatigue destructions. The paper reports the technological assurance options for resistance to fatigue by means of the control of such surface layer state parameters of machinery as dislocations density and a grain size of structure material.

Acoustic inversion for Monin-Obukhov similarity parameters from wind noise in a convective boundary layer.

The prediction accuracy of outdoor sound is in large part limited by uncertainties in the state of the atmosphere. These uncertainties can potentially be reduced by inferring scaling parameters of the atmospheric surface layer from wind noise. Screened microphones sense wind noise as a result of mean atmospheric flow, turbulent eddy interaction with the windscreen, and pressure fluctuations within the turbulent flow. Under conditions of terrain homogeneity and atmospheric quasi-steadiness, the Monin-Obukhov similarity theory (MOST) states that only a handful of parameters governs the dynamics of the atmospheric surface layer. This study explores the relationships of atmospheric similarity parameters to the acoustic spectrum of wind noise in a convective boundary layer. Ambient noise data collected in a high desert during a 2007 long-range sound propagation experiment are analyzed for the purposes of establishing a nondimensional empirical relationship between the acoustic power spectrum and MOST parameters. Furthermore, this paper examines the consequences of inferring surface-layer scaling parameters with different parameter priors. This study shows that, for minimizing the variance in the inversion, the most important parameter to constrain is the Obukhov length.

Investigation of the pressure–strain-rate correlation and pressure fluctuations in convective and near neutral atmospheric surface layers

The pressure–strain-rate correlation and pressure fluctuations in convective and near neutral atmospheric surface layers are investigated. Their scaling properties, spectral characteristics, the contributions from the different source terms in the pressure Poisson equation and the effects of the wall are investigated using high-resolution (up to $2048^{3}$) large-eddy simulation fields and through spectral predictions. The pressure–strain-rate correlation was found to have the mixed-layer and surface-layer scaling in the strongly convective and near neutral atmospheric surface layers, respectively. Its apparent surface-layer scaling in the moderately convective surface layer is due to the slow variations of the mixed-layer contribution, and is an inherent problem for single-point statistics in a multi-scale surface layer. In the strongly convective surface layer the pressure spectrum has an approximate $k^{-5/3}$ scaling range for small wavenumbers ($kz\ll 1$) due to the turbulent–turbulent contribution, and does not follow the surface-layer scaling, where $k$ and $z$ are the horizontal wavenumber and the distance from the surface respectively. The pressure–strain-rate cospectrum components have a $k^{-1}$ scaling range, consistent with our prediction using the surface layer parameters. It is dominated by the buoyancy contribution. Thus the anisotropy in the surface layer is due to the energy redistribution caused by the density fluctuations of the large eddies, rather than the turbulent–turbulent (inertial) effects. In the near neutral surface layer, the turbulent–turbulent and rapid contributions are primarily responsible for redistribution of energy from the streamwise velocity component to the vertical and spanwise components, respectively. The pressure–strain-rate cospectra peak near $kz\sim 1$, and have some similarities to those in the strongly convective surface layer for $kz\ll 1$. For the moderately convective surface layer, the pressure–strain-rate cospectra change signs at scales of the order of the Obukhov length, thereby imposing it as a horizontal length scale in the surface layer. This result provides strong support to the multipoint Monin–Obukhov similarity recently proposed by Tong &amp; Nguyen (J. Atmos. Sci., vol. 72, 2015, pp. 4337–4348). We further decompose the pressure into the free-space (infinite domain), the wall reflection and the harmonic contributions. In the strongly convective surface layer, the free-space contribution to the pressure–strain-rate correlation is dominated by the buoyancy part, and is the main cause of the surface-layer anisotropy. The wall reflection enhances the anisotropy for most of the surface layer, suggesting that the pressure source has a large coherence length. In the near neutral surface layer, the wall reflection is small, suggesting a much smaller source coherence length. The present study also clarifies the understanding of the role of the turbulent–turbulent pressure, and has implications for understanding the dynamics and structure as well as modelling the atmospheric surface layer.

Turbulence characteristics of surface boundary layer over the Kalpakkam tropical coastal station, India

In this study turbulent fluxes and their intensity features are studied in different seasons at the tropical Indian coastal station, Kalpakkam. Measurements from Ultrasonic anemometer at 10 m agl over 30-day period of four seasons (winter 1–30 January; summer/spring 1–30 April; SW monsoon 1–30 July; NE monsoon 1–30 October) in 2013 and 2014 are used for this work. Various surface layer parameters viz, friction velocity (u*), Obukhov length (L), momentum flux (M), turbulent heat flux (H), turbulence kinetic energy (TKE) are computed using eddy correlation method. Results indicate that the study region is highly turbulent in summer followed by NE monsoon, winter and SW monsoon seasons. Derived parameters indicate that shear is the main contributing mechanism for TKE generation during SW monsoon and both shear and buoyancy contributed for the generation of TKE in other seasons. Site specific turbulent intensity relationships were developed by analyzing second order moments of 3D wind components as a function of stability parameter (z/L). The turbulent components of wind followed 1/3 power law in the unstable regime and − 1 power law in the stable regime. Comparisons with previous studies indicate that the turbulent intensity for horizontal winds at the coastal station is relatively less especially in the unstable conditions. The derived relationships are found to be unique and vary seasonally and suggest their application for improved modeling of atmospheric dispersion in the study domain. Rate of dissipation of TKE (ϕe) for stable and unstable conditions at the observation site is different from the earlier proposed relationships in the literature. Thus, a new relationship is proposed for the better fit of the data at this site.

Contrasting variations in the surface layer structure between the convective and non-convective periods in the summer monsoon season for Bangalore location during PRWONAM

An attempt has been made here to examine the contrasting variations in mean surface layer parameters including surface fluxes, and in surface layer stability between the convective and non-convective periods in the southwest monsoon season for the Bangalore experiment location (12.54° N, 77.22° E). The micrometeorological measurements analysed during 2009 and 2010 are from the instrumentation network established during the programme, “Prediction of Regional Weather using Observational meso-Network and Atmospheric Modelling (PRWONAM)”.The Short Wave (SW) radiative flux at the surface is observed to be respectively at 799 ± 188 Wm−2 (772 ± 195 Wm−2) and 436 ± 113 Wm−2 (257 ± 101 Wm−2) at 12:00 LT (Local Time, UTC+05:30) during the non-convective and convective periods in 2009 (2010). The significant difference in SW radiative flux is due to the difference of cloud cover between the non-convective and convective periods. This significant reduction of 515 W m−2 at 12:00 LT in SW radiative flux caused maximum cooling in skin temperature (air temperature) by 6.2 °C (3.8 °C) at 12:00 LT (18:30 LT) from 30.8 ± 3.9 °C (27.1 ± 1.4 °C) in the non-convective period. The impact of convection on soil temperature is observed up to 0.2 m deep. The diurnal amplitudes in composites of air temperature are 8.4 °C (8.4 °C) and 5.7 °C (4.7 °C) during the non-convective and convective periods respectively in 2009 (2010); and the amplitudes in relative humidity are 41.5% (39.7%) and 29% (22.8%).Low wind speeds prevailed 63.4% of the time, all through the day and night, in the monsoon season. The diurnal variations in wind speed during the convective period showed higher variability than in non-convective period. The momentum flux varied in accordance with the strength of the wind speed during the monsoon seasons of both the years 2009 and 2010. The peak sensible heat flux in the convective period is noted to be smaller than that in the non-convective period by 128 W m−2 in 2009 and 124 W m−2 in 2010. The moisture flux showed no significant variations between the two periods. Sensible heat and moisture flux peaked up at 334 W m−2 and 258 W m−2 respectively at low wind strong unstable situation.

Integrated Method of Study of Hardened of Details

The provision of certain information regarding the surface layer of the equipment parts is one of the critical issues for the modern mechanical engineering. The development of new technologies of protective-strengthening treatment of critical parts surface requires the development of improved methods for surface layer material state assessment as a result of high-energy impact typical for ion-plasmatic, ion-implantation and combined treatment method. Moreover, the peculiarities of industrial mechanical engineering production require the development of simple and efficient methods of surface layer parameters checkout. The application of protective coatings complicates the use of universal method of the parts surface layer parameters assessment. The present article is devoted to the development and studying of a new method for the parts surface layer state assessment after its treatment of various types, including the protective-strengthening technologies and the application of protective coatings. The specific features of the proposed assessment method are its simplicity, reliability, and universality.

Physicochemical environment of Malala Lagoon in Southern Sri Lanka

Malala Lagoon is the largest of the five enclosed shallow lagoons in Bundala National park, and is one of the most productive of the fifteen lagoons in the Hambantota district, Sri Lanka. It has been vulnerable to human induced pollution for nearly three decades. This paper ascertains the status of physicochemical environment of the lagoon and its temporal variation from 1995 to 1997. During the study period physicochemical and biological parameters measured in Malala lagoon were water temperature, pH, conductivity, Secchi depth, dissolved oxygen, salinity, total alkalinity, dissolved phosphate, and chlorophyll-a, and their mean values were; 27.69 ± 1.62°C, 7.93±0.46, 5.14±3.88 mS/cm, 00.39 ± 00.19 m, 7.83±0.89 mg/L, 2.18±1.61‰, 2.14 ±0.59 mmol/L, 12.25±4.67 mg/L and 8.86 ± 4.62 mg/L respectively. Maximum depth of the lagoon rarely exceeded 2 m during the study period. Due to the shallowness of the lagoon, there were no significant differences (p&gt;0.05) in physicochemical parameters of surface, middle and bottom layers of the water column. Water level of the lagoon showed a significant (p&lt;0.01) negative correlation with electrical conductivity (r = 0.727) as well as with the salinity (r = 0.729). Water influx to the lagoon showed a significant (p &lt; 0.05) negative correlation with conductivity (r = 0.454) and salinity of the lagoon (r = 0.406). Findings of the study are compared with those carried out over a decade to explore and elucidate the long term changes in the lagoon environment. When compared with the published data from preceding and subsequent studies, it confirmed that the brackish water characteristics of the lagoon are gradually degrading due to pollution caused by natural phenomena and anthropogenic activities adversely affecting the ecological balance and the productivity of the lagoon. These findings could be of great importance when studying long term changes in the coastal waters, which are essential for sustainable coastal planning, with respect to socioeconomic development programmes as well as to identify the impacts of Hambantota port and maritime activities in the area and to understand the trends related to global climate change.

Definition of criteria for estimating alternative technologies of increasing quality of rotor shaft neck by electroerosive alloying and surface plastic deformation methods

There are represented the results of influence of the surface plastic deformation (SPD) methods, namely, diamond smoothing (DS) and ball-rolling surface roughness generation (BSRG) ones on the qualitative parameters (residual stresses, fatigue strength and wear resistance values) of the steel substrate surface layers formed by the electroerosive alloying (EEA) method. There are proposed the most rational methods of deformation and also the composition for electroerosive coatings providing the presence of the favorable residual compressive stresses in the surface layer, increasing fatigue strength and wear resistance values. There are stated the criteria for estimating the alternative variants of the combined technologies and choosing the most rational ones thereof.

Inversion Build-Up and Cold-Air Outflow in a Small Alpine Sinkhole

Semi-idealized model simulations are made of the nocturnal cold-air pool development in the approximately 1-km wide and 100–200-m deep Grunloch basin, Austria. The simulations show qualitatively good agreement with vertical temperature and wind profiles and surface measurements collected during a meteorological field expedition. A two-layer stable atmosphere forms in the basin, with a very strong inversion in the lowest part, below the approximate height of the lowest gap in the surrounding orography. The upper part of the stable layer is less strongly stratified and extends to the approximate height of the second-lowest gap. The basin atmosphere cools most strongly during the first few hours of the night, after which temperatures decrease only slowly. An outflow of air forms through the lowest gap in the surrounding orography. The outflow connects with a weak inflow of air through a gap on the opposite sidewall, forming a vertically and horizontally confined jet over the basin. Basin cooling shows strong sensitivity to surface-layer characteristics, highlighting the large impact of variations in vegetation and soil cover on cold-air pool development, as well as the importance of surface-layer parametrization in numerical simulations of cold-air-pool development.

Micrometeorological Tower Observations and its Importance in Atmospheric Modelling and Space Technology

Background/Objectives: The assessment of turbulence parameters is important for understanding the heat, momentum exchange and pollutant dispersion at any given site. Methods/Analysis: Continuous micrometeorological data were collected at SRM University, Kattankulathur (12o 48’ N to 12o 49’ N; 80o 02’ E to 80o 03’ E) a sub-urban area near Chennai by a 16 m meteorological mast. Data with conventional sensors were obtained for wind, temperature, and humidity from August 2010 to March 2015. Findings: The gradient observations were analyzed to explore the atmospheric surface layer parameters and were used in atmospheric dispersion modeling. Wind and temperature data were analyzed to understand their diurnal and seasonal variations. The Inter-relationships of temperature and wind pattern were discussed and the diurnal variations of temperature and wind profile were plotted for a particular month during study period to assess the Climate pattern ofa particular study period. This study may play a vital role in atmospheric modeling and also in space vehicle launching.

Variability of the Tropospheric-Delay Temporal Structure Function of Radio Signals from the Global Navigation Satellite Systems Versus Tropospheric Surface Layer Parameters

We present the results of a four-year (2009–2012) study of the decimeter radio wave propagation using signals from the global navigation satellite system (GNSS) and simultaneous measurements of the tropospheric surface layer parameters in the city of Kazan. Inter- and intra-annual variabilities of the temporal structure functions of the zenith tropospheric delay (ZTD) of decimeter radio waves are analyzed. It has been found that the contribution of irregularities with time scales of up to 24 h to the ZTD fluctuation variance varies, depending on the surface weather parameters (temperature and pressure). Correlation coefficient between the approximation exponents of the ZTD temporal structure function of decimeter radio waves and surface temperature reaches 0.77 for fluctuations with time scales of up to 8 h. It has been established that synoptic processes and the underlying surface affect the formation of mesoscale fluctuations on the phase path of radio signals from the navigation satellite systems.

ЭКСПЕРИМЕНТАЛЬНОЕ ИССЛЕДОВАНИЕ ФОРМООБРАЗУЮЩИХ ПРОЦЕССОВ ПРИ ОБРАБОТКЕ АЛЮМИНИЕВЫХ СПЛАВОВ

It is well known that machining aluminum and its alloys is accompanied by very considerable changes in quality parameters of parts surface layers which affect greatly performance attributes. The study of the machining conditions influence upon surface layer quality in parts allows defining optimum cutting parameters and increasing performance attributes of many parts. It is well known that there are alternative methods of shaping which are a combined treatment which can include a mechanical, electrical and chemical influence upon a surface worked. Combined methods of treatment possess a wide range of controlled factors affecting a quality level of a surface formed and that is why they are convenient and effective in use during processes of shaping in parts made of difficult-to cut and heterogeneous materials. As the investigation results have shown during edge cutting machining anodic-mechanical treatment in the course of cutting Al 2 and Al 3 silumins the oxides formation on the surface worked worsens considerably electrochemical processes. Particularly it is significant at anodic dissolution of aluminum alloys having a high capacity to oxidation. The method of electromechanical combined treatment allows managing qualitative indices in the course of surface shaping and as a result promoting the achievement of an essential level in quality parameters of a surface level.

The Thickness Dependence of Thermoelectric Parameters of thin Films Based on Compounds LAST

The thermoelectric properties of thin films based on compounds PbSnAgTe, obtained by condensation of vapor on the high vacuum on mica substrate are researched. Based on a two-layer model Petrits are founded electrical parameters of surface layers. It is shown that condensates thickness d &lt; 500 nm are characterized by improved thermoelectric properties.