Vertical Component Of Wind Velocity Research Articles

The Impact of Internal Gravity Waves on the Spectra of Turbulent Fluctuations of Vertical Wind Velocity in the Stable Atmospheric Boundary Layer

The wave turbulence interactions in the stable boundary layer (SBL) of the atmosphere are studied based on data from lidar measurements of the vertical component of wind velocity during the propagation of internal gravity waves (IGWs). It is shown that as an IGW appears, the amplitude of the spectra of turbulent fluctuations of vertical wind velocity nearby the frequency of quasi-harmonic oscillations induced by an IGW increases significantly, sometimes by several orders of magnitude, compared to the spectra in the absence of an IGW. Since IGW energy is transferred to small-scale turbulence, the amplitude of spectra with the Kolmogorov–Obukhov −5/3 power-law frequency dependence in the inertial frequency range increases. The slope of the spectra in the low-frequency range between the frequency of IGW-induced oscillations and the frequency of the lower boundary of the inertial range exceeds the slope, corresponding to the −5/3 power-law dependence. In this frequency range, the spectra obey the power-law dependence on the frequency with the exponent ranging from −4.2 to −1.9. The average value of the exponent −3 is consistent with a low-frequency slope caused by IGWs in turbulent spectra in the lower SBL.

Evaluation of the Wind Environment around Multiple Urban Canyons Using Numerical Modeling

This study aimed to evaluate the wind environment in step-up and step-down urban canyons through a computational numerical experiment using the computational fluid dynamics (CFD) model. Spatial structural conditions were considered according to the location of high-rise buildings, and the changing wind patterns inside canyons were compared and analyzed by varying the building heights. Under the step-up to step-down condition, wind velocity inside the canyon weakened, a vertical vortex formed, and vertical air flow separated; additionally, in shallow and deep canyons, wind velocity and detailed flow differed slightly according to each additional condition. For the step-down to step-up condition, the building located in the center appeared to be isolated, and a general wind environment phenomenon consistent with the step-up and step-down structures was observed. However, depending on the isolated area, an additional roof-top canyon was formed, and the wind field in the canyon was found to affect the wind velocity and detailed flow in other canyons. The wind velocity components of the inflow and outflow winds into the canyon differed based on the step-up to step-down or step-down to step-up conditions, and according to the conditions in the first and second canyons. Furthermore, the vertical wind velocity components were greatly affected by the step-up and step-down structures. Accordingly, the height and structural location of the building could affect various phenomena, such as the separation of vortices and air currents inside the canyon, and a variable wind environment was formed according to a series of conditions for the building.

Turbulent Momentum Flux Behavior above a Fire Front in an Open-Canopied Forest

Atmospheric turbulent circulations in the vicinity of wildland fire fronts play an important role in the transfer of momentum into and out of combustion zones, which in turn can potentially affect the behavior and spread of wildland fires. The vertical turbulent transfer of momentum is accomplished via individual sweep, ejection, outward interaction, and inward interaction events, collectively known as sweep-ejection dynamics. This study examined the sweep-ejection dynamics that occurred before, during, and after the passage of a surface fire front during a prescribed fire experiment conducted in an open-canopied forest in the New Jersey Pine Barrens. High-frequency (10 Hz), tower-based, sonic anemometer measurements of horizontal and vertical wind velocity components in the vicinity of the fire front were used to assess the relative frequencies of occurrence of the different types of momentum-flux events, their contributions to the overall momentum fluxes, and their periodicity patterns. The observational results suggest that the presence of surface fire fronts in open-canopied forests can substantially change the sweep-ejection dynamics that typically occur when fires are not present. In particular, sweep events resulting in the downward transport of high horizontal momentum air from above were found to be more prominent during fire-front-passage periods.

Characteristics and similarity relations of turbulence dispersion parameters under heavy haze conditions

The parameterizations of atmospheric turbulence dispersion in many commonly used numerical models are based on the similarity relations in highly flat and sparsely populated areas. Such parameterizations limit the applicability of the models for simulating heavy haze processes that frequently occur in densely populated urban areas with complex terrains. In this study, we examined the similarity relations of key turbulence dispersion parameters in the Lagrangian dispersion models, including the turbulent standard deviations, high-order moments (the third and fourth moments), and integral time scales for longitudinal, lateral, and vertical wind velocity components during heavy haze days in downtown Beijing, China. The similarity relations were analyzed in the framework of the local similarity theory, which is commonly used in studies of urban turbulence. It was found that in highly stable or unstable conditions, the normalized turbulent standard deviations and high-order moments (the normalized integral time scales) during heavy haze days generally increased (decreased) significantly slower than those during clean days. However, in nearly neutral conditions, the normalized values for heavy haze and clean days were approximately equal. The results indicate that the development of parameterizations of turbulence dispersion during heavy haze days, especially in highly stable or unstable conditions, warrants greater research focus.

Revisiting aerodynamic admittance functions of bridge decks

A framework was proposed to identify a comprehensive set of aerodynamic admittance functions for bridge decks. The contributions of the cross-spectra between longitudinal and vertical wind velocity components and between turbulence components and gust-induced forces were embedded in the identification procedure. To facilitate application of the identified functions in engineering practice, the concept of an equivalent aerodynamic admittance function was introduced and numerically validated. The equivalent aerodynamic admittance functions of a set of streamlined and bluff cross sections were identified experimentally in a wind tunnel. Buffeting analysis of a bridge deck was carried out and the response predicted using the identified aerodynamic admittance functions compared well with the measured response. In addition, a sensitivity analysis was performed to delineate the influence of aerodynamic and structural parameters on the buffeting response, thereby demonstrating the significance of the proposed identification framework.

Measurement of momentum flux using two meteor radars in Indonesia

Abstract. Two nearly identical meteor radars were operated at Koto Tabang (0.20° S, 100.32° E), West Sumatra, and Biak (1.17° S, 136.10° E), West Papua, in Indonesia, separated by approximately 4000 km in longitude on the Equator. The zonal and meridional momentum flux, u′w′ and v′w′, where u, v, and w are the eastward, northward, and vertical wind velocity components, respectively, were estimated at 86 to 94 km altitudes using the meteor radar data by applying a method proposed by Hocking (2005). The observed u′w′ at the two sites agreed reasonably well at 86, 90, and 94 km during the observation periods when the data acquisition rate was sufficiently large enough. Variations in v′w′ were consistent between 86, 90, and 94 km altitudes at both sites. The climatological variation in the monthly averaged u′w′ and v′w′ was investigated using the long-term radar data at Koto Tabang from November 2002 to November 2013. The seasonal variations in u′w′ and v′w′ showed a repeatable semiannual and annual cycles, respectively. u′w′ showed eastward values in February–April and July–September and v′w′ was northward in June to August at 90–94 km, both of which were generally anti-phase with the mean zonal and meridional winds, having the same periodicity. Our results suggest the usefulness of the Hocking method.

Analysis of wind vertical component characteristics in the stratosphere

Height, time, and latitude dependences are analyzed of zonal mean vertical component of wind velocity for the period of 1992–2006 from the UKMO atmospheric general circulation model. It is shown that the ascending wind speed can provide vertical transport, against gravity, of rather large (up to 3–5μm) aerosol particles with density to 1.0–1.5 g/cm3 in the stratosphere and mesosphere. The wind velocity vertical component is supposedly a significant factor of particle motion up to 30–40–km levels and can affect sedimentation rate and residence time of the aerosol particles in the stratosphere. Structure of the mean vertical component of wind velocity allows occurrence of dynamically stable aerosol layers in the middle stratosphere.

Investigation of Low-Frequency Perturbations Induced by a Steep Obstacle

Flow perturbation due to the orographic forcing at the top of a steep ridge has been investigated. Spectral and wavelet analyses of longitudinal and vertical wind velocity components highlight the presence of low-frequency perturbations produced by topography. Wavelet kurtosis reveals the intermittent character of these perturbations. The application of a multi-resolution data filter allows the detection of the topographically forced structures and the consequent statistical characterisation. The detected topographically forced structures remain active only for a 15% of the time on average. Nevertheless, they appear very efficient in the momentum transport, accounting for about 50% of the downward momentum flux produced in the low frequency range. Quadrant analysis highlights how topographical forcing produces the weakening of ejections and the strengthening of sweeps at the top of the ridge.

The Value Of The β Coefficient In The Relaxed Eddy Accumulation Method In Terms Of Fourth-Order Moments

The commonly measured value ofβ in the relaxed eddy accumulationmethod of about 0.56is shown to arise from the non-Gaussiannature of turbulence. Fourth-orderGram–Charlier functions forthe two-dimensional probability distributionsof variation in the horizontal component of wind velocityand concentrations of water vapour, carbondioxide and methane with respect to thevertical component of wind velocity are used to examinethe value of β.An analytical solution for β ispresented in terms of fourth-order moments.Under mean conditions, this solution givesa value for β of0.557. Variation of β is shown to be controlledprimarily by the ratio of the mean ofc'w′3 (where c'is relevant to the entity of interest andw' is vertical component of windvelocity) to the correlationcoefficient between the entity concentrationand vertical component of wind velocity.

Characterization Of Atmospheric Turbulence By Dynamical Systems Techniques

We describe a dimensional analysis for different time series of the vertical component of wind velocity from half-hourly sonic anemometermeasurements. The goal is a characterization of the atmospheric turbulence fromthe point of view of Dynamical Systems Theory, based on the correlation dimension of the strange attractor. Our results suggest that the convective turbulence correlation dimension (values ≈ 6) is lowerthan the mechanical one (values ≈ 7–9).

Aircraft assessment of trace compound fluxes in the atmosphere with relaxed eddy Accumulation: Sensitivity to the conditions of selection

The Relaxed Eddy Accumulation (REA) technique, implemented aboard aircraft, may be used to measure a wide variety of trace gas fluxes at a regional scale. Its principle is rather simple: air is sampled at a constant rate and the flux is calculated by multiplying a constant β (0.58 in field experiment and 0.62 in simulations) by the standard deviation of the vertical velocity and by the difference between the average concentrations of the scalar (trace gas) for updrafts and downdrafts. The storage of the chemical compound in reservoirs allows for trace gas analysis in laboratory, when in situ measurement with fast response and high sensitivity sensors are not available. The REA method was implemented on the Avion de Recherche Atmosphérique et de Télédétection aircraft during the Experiment for Regional Sources and Sinks of Oxidants (EXPRESSO) campaign. The main requirement for accurate flux determination is the measurement of the vertical component of wind velocity in real time. A simulation technique was developed to evaluate the performance of an aircraft REA. The influence of the time lag between the vertical velocity (W) measurement and REA control was tested, as well as the offset of W, the threshold, and the filtering imposed on W. Correction factors, used in a deployment of aircraft REA, were deduced from this study. An additional simulation was performed to evaluate the influence of spatial or temporal drifts on the scalar. The simulation showed that the REA method is not more disturbed than the Eddy Correlation method by low frequencies of physical origin, such as topography. The REA method was used during EXPRESSO for the measurement of isoprene fluxes over the wet savanna and the evergreen rain forest.

Effects of hostile terrains on wind turbine performances and loads: The Acqua Spruzza experience

The siting activity carried out by ENEL since 1979 has led to the conclusion that exploitable wind conditions can be found mainly on the ridges of Central and Southern Apennines. Mountaineous areas, on the other hand, are often located above 1000 m a.s.l., where very harsh conditions (heavy icing, snowfalls, high turbulence, high vertical component of wind velocity, etc.) can occur, especially during winter months; furthermore, they generally feature complex profile of terrain. Very little experience has been gained worldwide of operating wind turbines in very hostile conditions. The need for research about the feasibility of wind plants and the viability of present commercial medium-sized wind turbines in such prospective location led to the construction of a mountain test site at Acqua Spruzza on the Apennines, where a thorough testing activity is being carried out, aimed at assessing, among other things, the performances and lifetime of machines.

Cup Anemometer Behavior in Turbulent Environments

Abstract The behavior of the cup anemometer rotor in turbulent atmospheric flow is discussed in terms of a general equation of motion. This equates the rate of change s of the rotation rate s of the rotor to a forcing F(s, h, w), which is proportional to the torque and a function of s and of the total horizontal and the vertical wind velocity components, h, and w, respectively. To determine the so-called overspeeding, it is necessary to carry out first-and second-order perturbation calculations around the response curve obtained in a laminar flow. From this curve, which for the purpose of this paper can be considered linear, five constraints are derived between the first and second partial derivatives of F. These constraints provide sufficient information for deriving an expression for the overspeeding to which four distinctly different biases contribute—one for each of the velocity components and one from the covariance between streamwise velocity components ũ and w. A phenomenological model of...

Boundary-layer flow structures associated with particle reentrainment

Measurements of near-surface longitudinal and vertical wind velocity components associated with particle reentrainment from a flat surface have been examined in a wind tunnel. Sparsely covered particle beds were used to assure that observed reentrainment events resulted primarily from the action of fluid forces. Characteristic velocity patterns were found to be associated with a majority of particle reentrainment events examined. These characteristics have been categorized and examined as ensemble averages. The flow pattern most frequently observed during particle reentrainment was termed Ejection-Sweep (E-S) and is very similar to organized fluid motions previously observed in laboratory flows and in the atmospheric boundary layer. A simple two-tiered E-S pattern recognition scheme is described which strives to identify particle reentrainment events objectively based on flow characteristics alone. The first step is to identify potential E-S patterns using criteria which identify a characteristic longitudinal acceleration, and the second step is to use threshold values of pattern characteristics to accept or reject these first-tier patterns. Pattern recognition results are presented in terms of the ability to identify reentrainment events versus false identifications, and show an exponential growth in false identifications with an increasing number of reentrainment events identified.

Structure of the vertical velocity field analyzed with a Doppler Sodar

Fifteen hours of Sodar echoes, collected during the 4th Environmental CEC Campaign at Turbigo, Italy, in September 1979, have been analyzed. We discuss the vertical profiles and the time evolution of the second and third statistical moments of the vertical component of wind velocity, measured at a rate of one height-profile every 6 s for a height range of 1000 m and a vertical resolution of 29 m. We also analyze the power spectra of the vertical velocity.

Clear air Doppler radar measurements of the vertical component of wind velocity in the troposphere and stratosphere

We discuss three techniques for using a Doppler radar to deduce the vertical component of the wind velocity in the optically clear atmosphere. These techniques involve operating the radar antenna in three different modes: 1) scanning along almucantar circles (azimuth scans), 2) scanning along vertical circles (elevation scans), and 3) leaving the antenna fixed at the zenith. Results obtained from the Chatanika, Alaska radar facility are presented which show that below about 5 km altitude, all three methods give essentially the same results. Above this altitude, the first two methods become increasingly subject to errors arising from the effect of large scale atmospheric inhomogeneities and thus give less reliable vertical velocities. The zenith method gives accurate vertical velocities for all altitudes within its range.

Theory of tracer distribution near the ground

The peculiarities of tracer distribution in ground-layer air are investigated on the basis of the solution of the differential equation of turbulent diffusion. The use of numerical methods of solution and an electronic computer allowed us to calculate the concentration field from elevated sources under natural conditions of changes of horizontal and vertical wind velocity components and exchange coefficients. The use of both light and heavy pollutants as tracers is considered. Possibilities of using tracers under anomalous meteorological conditions when increased concentrations (elevated inversions, calms, etc.) can be created in the ground-layer air are also examined. The relationship between pollutant concentration from the source both in the presence and in the absence of wind is analyzed. The velocity field of air currents over rough terrain is studied theoretically by integration of the equation of motion. Air currents over some kinds of relief (hills and hollows) are investigated. For these problems, turbulent exchange is taken into consideration and potential currents near various forms of underlying surface are used for more schematic calculations. The field of vertical and horizontal velocity and turbulence is also determined on models with the help of wind-tunnel experiments. Characteristic forms of cross terrain and city buildings of old and new types are modeled.

Introductory theory for upper atmosphere wind and sonic velocity determination by sound propagation

The problem is considered of deriving the mean values of the horizontal wind velocity components u( z), v( z) and the velocity of sound c( z), averaged with respect to height z along a sound-ray travelling between two known points in the atmosphere, from measurements of the time of travel of the ray between these points and the co-ordinates of the ray. It is shown that, for a ray which does not suffer total reflection, expressions can be derived for u(z) , v(z) , and c(z) in terms of the measured quantities, and the mean value of the vertical component of wind velocity w( z), provided the variations in u( z), v( z), w( z), and c( z) with height are sufficiently small. The theory is carried further by working out in detail the second order contributions to u(z) , v(z) , and c(z) which arise from the variations in u( z), v( z), w( z), and c( z). Using typical atmospheric data, the more important of these second-order terms are evaluated numerically for the case of a sound-ray received at an observation point on the ground from a source at any height up to 90 km. It is shown that the contributions from these terms to u(Z) , v(z) , and c(z) are less than 0.8 m/sec when the ray lies near the vertical. For a ray which departs appreciably from the vertical (inelination about 45°), the contributions amount to a few metres per second, but are unlikely to exceed about 8 m/sec unless exceptionally large wind velocities are present.

自然風に於ける變動速度の垂直成分の測定

自然風に於ける變動速度の垂直成分の測定