Wind Direction Measurements Research Articles

Form–flow interactions of an aeolian saucer blowout

AbstractAirflow patterns through a saucer blowout are examined from wind speed and direction measurements made during a chinook wind event. The blowout long‐axis is oriented east–west with a broad depositional apron on the east side. Wind directions during the event rotated from south‐westerly to westerly, permitting an assessment of oblique and axis‐parallel flows. Results show that airflow passing over the windward rim of the saucer blowout expands and decelerates, leading to flow separation and a small re‐circulation zone on sheltered lee slopes. Near the deflation basin, airflow re‐attaches to the blowout surface and accelerates up to a small opening in the east rim, where it can be up to 50% faster than on the windward edge. Beyond the downwind rim the airflow expands and decelerates and sand is deposited onto a broad apron. Similar to coastal trough blowouts, the degree of airflow steering and acceleration along the deflation basin is determined by the angle of incidence between the approach wind and the long‐axis of the blowout. As the angle of incidence increases wind speed accelerates at 0·3 m above the surface of the deflation basin and the degree of airflow steering increases. Overall, a two‐fold process is identified, where south‐westerly flows have greater potential for eroding the deflation basin, while westerly flows have greater potential for evacuating sand from within the blowout. Visual observations indicate that sand eroded from the deflation basin during south‐westerly flows is re‐distributed to adjacent zones of low wind speed until axis‐parallel winds evacuate the sand through the opening in the east rim. Morphometric changes since 1994 indicate that the blowout morphology has remained relatively constant, suggesting a persistent interplay between oblique and axis‐parallel wind erosion events. Collectively, these findings indicate that the angle of approach winds is an important control on saucer blowout morphodynamics. Copyright © 2009 John Wiley & Sons, Ltd.

Atmospheric stagnation, recirculation and ventilation characteristics at Kakrapar atomic power station site

This paper describes the meteorological characteristics of Kakrapar Atomic Power Station (KAPS) site (inland site) by using the integral parameters developed by Allwine and Whiteman. Meteorological data measured during the period 1995–2000, were analysed. The integral quantities related to the occurrence of stagnation, recirculation and ventilation characteristics were studied for KAPS site to asses the dilution potential of the atmosphere. Wind run and recirculation factors were calculated for a 24-h transport time using 6 years of hourly surface measurements of wind speed and direction. The occurrence of stagnation, recirculation and ventilation characteristics during 1995–2000 at KAPS site is observed to be 19.2% of the time, 21.0% of the time and 40.0% of the time, respectively. The presence of strong monsoon winds with predominant wind direction SW during monsoon season lead to higher ventilation (60.4% of the monsoon season). The presence of light winds and more dispersed winds during winter season with predominant wind directions E and ENE resulting more stagnation (26.5% of the winter season) and recirculation (32.6% of the winter season). Thus this study will serve as an essential meteorological tool to understand the transport mechanism of atmospheric releases from any industry including nuclear industry.

Mean wind speed profiles in the air basin of Moscow

Results of measurements of mean wind speed profiles and direction during two years in the center of the city of Moscow are presented. These measurements were performed with a Doppler acoustic profiler (sodar), which was used for continuous monitoring of the wind speed within the height range from 40 to 250–500 m. The averaged seasonal mean profiles are presented along with other observational data, including diurnal cycle parameters, wind speed and direction frequencies at chosen levels, and frequencies and duration of strong winds and calm weather.

Wind effects on noise propagation for complicated geographical and road configurations

Outdoor propagation from roads is influenced by wind, temperature and humidity. It is necessary to predict wind effects to simulate long-term environmental noise accurately. Noise levels have been measured in conjunction with wind speed and wind direction measurements. These noise levels showed noticeable daily changes. Excess attenuations of noise levels were found to depend on the vector wind ( U vec). By relating the vector wind and observed sound attenuations under all wind conditions, the influence of wind can be more accurately predicted for purposes of simulating noise propagation.

Measurements of Wind Velocity and Direction Using Acoustic Reflection against Wall

The measurements of wind velocity and direction using an acoustic reflection against a wall are described. We aim to measure the spatial mean wind velocity and direction to be used for an air-conditioning system. The proposed anemometer consists of a single wall and two pairs of loudspeakers (SP) and microphones (MIC) that form a triangular shape. Two sound paths of direct and reflected waves are available. One is that of the direct wave and the other is that of the wave reflected on the wall. The times of flights (TOFs) of the direct and reflected waves can be measured using a single MIC because there is a difference in the TOF between direct and reflected waves. By using these TOFs, wind velocity and direction can be calculated. In the experiments, the wind velocities and directions were measured in a wind tunnel by changing the wind velocity. The wind direction was examined by changing the setup of the transducers. The measured values using the proposed and conventional anemometers agreed with each other. By using the wave reflected against a wall, wind velocities and directions can be measured using only two pairs of transducers, while four pairs are required in the case of conventional anemometers.

Two-dimensional ultrasonic anemometer using the directivity angle of an ultrasonic sensor

There has been continuous research on the ultrasonic sensors [L.C. Lynnworth, Y. Liu, Ultasonic flowmeters: half-century progress report 1955–2005, Ultrasonics (2006) 1371–1378]. This study used the directivity characteristic based on phase measurement, which ultrasonic sensor has. Transmitter has wide directivity, and in its range of directivity, receivers are located to measure wind direction and velocity. The velocity experiments which are the result of this production system indicate that the system error rate is 2%. The wind direction measurements also give the same result, an error of ±3°. This result is similar to existing anemometers. However, this new anemometer could possibly have a much higher sampling rate, operating circuit and system structure, which could be much simpler than the previous anemometer.

A Statistical Analysis of Wind Speed Distributions in the Area of Western Greece

The wind energy potential in Western Greece was evaluated from measurements of wind speed and direction at four weather stations. Data collected over a period of years were used to statistically analyze wind speed distributions. Weibull parameters, at the selected stations, were calculated using three different methods. The theoretical values calculated from the analysis of the collected data performed well with the measured ones. Finally, the correlation between Weibull parameters and the measured wind speed values was performed and analysed for each station.

Methane emissions from beef cattle - a comparison of paddock- and animal-scale measurements

Methane (CH4) emissions from a herd of 58 grazing cattle were determined in a field experiment using paddock-scale (micrometeorological) methods. The emissions were also measured daily from each animal, using the sulfur hexafluoride tracer method. The paddock-scale methods exploit how the gas, once emitted from the cattle, is transported and dispersed by the wind. Hence, the emission rate may be calculated from measurements of windspeed, wind direction and turbulence statistics, as well as CH4 concentration upwind and downwind of the herd. The paddock-scale methods include a mass-budget approach, flux-gradient method and gas dispersion model. Accuracy can be assessed in unprecedented detail because the animal-scale (reference) method included all individuals in the herd, and the measurement site was ideal for micrometeorological methods (flat, usually windy and free of obstructions that alter the turbulent airflow). The cattle were hand-reared steers of average weight 325 ± 20 kg. Based on the animal-scale method, the average CH4 emission rate over 9 days was 161 ± 20 g/steer.day. The gas dispersion model, when utilising vertical concentration profiles, yielded on average 27% greater emissions. The other paddock-scale methods agreed with the animal-scale method, provided the cattle were at least 22 m away from the location of the downwind concentration measurements. When the cattle were allowed to graze as closely as 5 m from the instruments, the paddock-scale methods gave greater emissions than the animal-scale method; reasons for this are discussed.

The influence of meteorological parameters on soil radon levels in permeable glacial sediments

The influence of meteorological parameters on soil radon concentrations in a permeable ice-marginal deposit in Kinsarvik, Norway, was investigated based on continuous measurements of soil radon concentrations, temperature, precipitation, wind speed, wind direction, air pressure and soil moisture content over a period of 10 months. The results show that the soil radon concentrations exhibit distinct seasonal and diurnal variations that predominantly are caused by changes in air temperature. Air flows between areas of different elevation occur in the ice-marginal deposit due to temperature differences between soil air and atmospheric air, and instantaneous changes in air flow direction were recorded when the atmospheric air temperature reached the average annual air temperature. Air pressure was found to be the second most important parameter influencing soil radon concentrations, while no apparent effect of precipitation, wind speed, wind direction or soil moisture was observed. Seasonal variations in indoor and soil radon levels were also investigated in a glaciofluvial deposit located 40 km southwest of Kinsarvik, and the close correlation between the seasonal variation patterns observed in the two areas suggests that the results of the Kinsarvik study also might be applicable to other areas of highly permeable building grounds where differences in terrain elevation exist.

Two-Axis Anemometer with Acoustic Reflector Using Single Pair of Loudspeaker and Microphone

In this paper, we describe a two-axis anemometer with an acoustic reflector using a single pair of a loudspeaker (SP) and a microphone (MIC). The two-axis anemometer proposed in this study consists of a SP, a MIC and an acoustic reflector, which form a right-angled isosceles triangle. This anemometer can measure spatial mean wind velocity and direction by calculating each wind component along the coordinate axis defined in each propagation path; this anemometer is targeted for use in air-conditioning systems of high efficiency. The sound probe consists of a SP, a MIC, an acoustic reflector and each propagation path. By using the acoustic reflector, an additional sound path becomes available. In this case, the time of flight (TOF) can be measured using a single SP–MIC pair because of the difference in TOF between direct and reflected waves. Some experiments were carried out in a wind tunnel to measure wind velocity and direction at various wind velocities. The sound probe is placed on a turntable in a wind tunnel. Although the actual wind direction is constant, the apparent direction relative to the sound probe can be changed by rotating a turntable. The measured wind velocities and directions in the experiments showed only small changes with the wind direction change. The feasibility and accuracy of the proposed two-axis anemometer for wind velocity and direction measurements were confirmed.

Computational Fluid Dynamics Modelling of the Pollution Dispersion and Comparison with Measurements in a Street Canyon in Helsinki

A measuring campaign was conducted in a street canyon (Runeberg St.) in Helsinki in 2003–2004. The concentrations of NOx, NO2, PM10 and PM2.5 were measured at street level and at roof level at an urban background location. This study utilises the data measured from 1 Jan to 30 April, 2004, when wind speed and direction measurements were also conducted on-site at the roof level. The computational fluid dynamics model ADREA-HF was used to compute the street concentrations, and the results were compared with the measurements. The predictions for the selected cases agreed fairly well (within < 25 % for 15 min average values) with the measured data, except for two cases: a windward flow in case of a low wind speed, and a moderate southerly flow parallel to the street canyon. The main reasons for the differences of predictions and measurements are the negligence of traffic-induced turbulence in the modelling and an under-prediction of ventilation of urban background air from a crossing street. Numerical results are presented for various example cases; these illustrate the formation of the vortices in the canyon in terms of the wind direction and speed and the influence of the characteristics of the flow fields on the concentration distributions.

The effects of surface moisture on aeolian sediment transport threshold and mass flux on a beach

AbstractThis paper presents results from a study designed to explore the effects of beach surface moisture and fetch effects on the threshold of movement, intensity of sand transport by wind and mass flux. The experiment was carried out over a period of five weeks at Greenwich Dunes, Prince Edward Island, Canada in May and June 2002. Moisture content was measured with a Delta‐T moisture probe over a 50 m by 25 m grid established on the beach. Measurements of wind speed and direction were made with arrays of cup anemometers and a two‐dimensional sonic anemometer. Transport intensity was measured at a height of 2–4 cm above the bed using omnidirectional saltation probes which count the impact of saltating grains on a piezoelectric crystal. Anemometers and saltation probes were sampled at 1 Hz. Sand transport was measured with vertical integrating sand traps over periods of 10–20 minutes. Results show that where there is a considerable supply of dry sand the saltation system responds very rapidly (1–2 s) to fluctuations in wind speed, i.e. to wind gusts. Where sand supply from the surface is limited by moisture, mean transport rates are much lower and this reflects in both a reduction in the instantaneous transport rate and in a transport system that becomes increasingly intermittent. Threshold wind speed is significantly correlated with an increase in surface moisture content near the upwind end of the beach fetch, but the relationship is not significant at the downwind end where sediment transport is initiated primarily by saltation impact from upwind. Mass flux increases with increasing fetch length and the relationship is described best by a power function. Further work is necessary to develop a theoretical function to predict the increase in transport with fetch distance as well as the critical fetch distance. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Assessment of snow transport in avalanche terrain

Abstract A local to regional assessment of transported snow during snow storms or subsequent periods of strong winds is a prerequisite to reliably estimate avalanche danger. Despite the fact that it has received continuing attention for decades, the problem of quantifying snow transport persists. Systems from point measurements to full three-dimensional simulations have been tested but all have their respective weaknesses. We present a new drift index, which has been tested and operated with some success in Switzerland. The index requires input from a wind-sheltered automatic weather station and a scaled wind speed from a wind-exposed site. Using the snow cover model SNOWPACK, the meteorological data is extrapolated to the four main aspects and snow cover development is calculated for these aspects. Depending on the measured wind direction and speed, a threshold condition for snow erosion at the upwind aspect is tested: if the wind is strong enough to erode the current snow at the surface of this aspect, the snow layer is eroded, transported and deposited onto the downwind aspect. With this scheme, the virtual, “representative” snow cover on the four main aspects in the vicinity of the meteorological stations are reconstructed for the course of the winter and the mass transport rate is converted to a lee-deposition drift index. A comparison with FlowCapt, an acoustic measurement device, which measures a local mass flux, shows that the measured mass flux correlates well with the amount of lee-slope deposition predicted by the drift index. Also, drifting snow periods are well detected by both the FlowCapt sensor and the SNOWPACK drift index and correspond to drifting snow periods reported by local observers. When comparing regional patterns of strong and weak snow transport as calculated from more than 110 automatic weather stations in the Swiss Alps with corresponding reports from local observers a good correlation is found, too. As opposed to earlier versions of the index, which had been based on flat field simulations of SNOWPACK alone, the new index no longer overestimates intensity and duration of blowing snow events. It is concluded that for the purpose of avalanche warning, the FlowCapt sensor and the SNOWPACK drift index are suitable means to quantify local to regional snow transport.

Maximum fluctuations of wind direction in limited time intervals at the levels up to 300 m from observations at a meteorological tower

On the basis of wind direction measurements with 1-s discreteness at the meteorological tower VMM-310 in the town of Obninsk, maximum fluctuations of wind direction are obtained with 10-s averaging over limited time intervals that correspond to the transport of pollutant puffs at distances about 10 km from the source at altitudes up to 300 m. Average values of maximum fluctuations of wind direction decrease with increasing wind speed, level of measurements, and stratification stability. Examples are presented of distributions of maximum fluctuations of wind direction as dependent of these factors. Parameters are given of distributions of maximum fluctuations of wind direction at six levels under different wind speeds and different atmospheric stability. The empirical distributions are approximated by Weibull distribution, and parameters of the latter are presented for separate levels. The results obtained can be used for estimation of an angular size of an area of possible pollution under different conditions of atmospheric stratification, wind speed, and levels of transport of an instantaneous puff of pollutants for the pollutant cloud motion up to a distance of 10 km from the source.

海浜埋立地の住宅地における開発に伴う風環境の変容 : 立地・気候特性に配慮した住宅地の通風計画手法に関する基礎的研究

This study clarifies relationships between residential development and the transformation of wind environment in a residential area on seaside reclaimed land. We first investigate the effects of buildings surrounding the site on the wind environment within the site, with regard to southerly summer winds, using both field measurement and CFD analysis, in order to clarify how geographic and climatic factors affect wind system formation. Next, we investigate the transformation of the wind environment as the residential development by measuring wind direction and velocity at six points within the site for a period of one year and three months. We then clarify the influences of outdoor wind environment on the natural ventilation of a house, built on the developed area, in the summer.

A satellite-derived climatology of global ocean winds

An interactive Climatology of Global Ocean Winds (COGOW) is presented based on 5 years (August 1999–July 2004) of QuikSCAT satellite measurements of wind speed and direction 10 m above the sea surface. This climatology provides the first high spatial resolution, observationally based, online atlas of ocean winds. Users can retrieve climatological wind maps and wind statistics, both in tabular and graphical form, from the COGOW web-based atlas. The global coverage of these data provides highly accurate information about the wind statistics in regions of the world ocean that are sparsely sampled by ships and buoys. A case study of the recovery of the vessel Ehime Maru off the Hawaiian Island of Oahu is presented to demonstrate the usage and value of COGOW. Evidence of air–sea interactions, one of many wind phenomena visible within COGOW, is discussed to further familiarize users with COGOW. Finally, the utility of COGOW with regard to various operational and research communities is summarized.

A remote‐sensing technique for the identification of aeolian fetch distance

AbstractThis paper describes a new method for assessing aeolian fetch distances in beach/dune systems. The remote‐sensing technique has advantages over currently used proxy measures of fetch distance, such as those based on tide gauges and beach profiles. The method uses a digital camera, global positioning system surveying, and a geographical information system software package to produce a rectified image of the beach surface. From this, direct measurements of the wet–dry beach boundary can be combined with wind direction measurements to determine fetch distance. The method offers an improvement on current approaches to sediment transport estimates: a 28‐day study on Magilligan Strand, Northern Ireland, showed that the commonly used high water mark approach overestimated fetch distance by 30% compared with the technique reported here.

Spaceborne observations of ocean glint reflectance and modeling of wave slope distributions

Measurements of wind speed and direction from the NASA Scatterometer and ocean reflectance from the POLDER multi‐directional radiometer are used for a quantitative analysis of the ocean glint intensity and shape. These two instruments have been flying on board the ADEOS satellite platform, which assures a very large data set of coincident measurements distributed over all oceans. The glint intensity and pattern is directly related to the wave slope probability function. The slope distribution model developed by Cox and Munk (1954) more than half a century ago, which is a function of wind speed and direction, permits an excellent fit of the observation. In particular, the modeled mean square slope is in near perfect agreement with that derived from the satellite data. The latter permit, however, a novel analysis of the deviations from a pure Gaussian slope distribution. In particular, it is shown that the skewness is a non‐linear function of the wind speed. A typical glint reflectance in the specular direction is 0.2, which is therefore significantly smaller than, for instance, a typical cloud reflectance. There are large variations with the Sun zenith angle, however, that are easily accounted for with a simple formula. The glint reflectance allows an estimate of the wind speed that is highly correlated with the independent measurement from the scatterometer, with an estimated error less than 1 m s−1. The multidirectional reflectance measurements from POLDER also permit the retrieval of the wind direction, albeit only in favorable conditions depending on the respective orientation of the view and wind vectors.

Fire spread experiment across Mediterranean shrub: Influence of wind on flame front properties

A fire spread experiment was conducted in the field under wind-blown conditions. The fuel consists of tall and dense Mediterranean shrub vegetation. The plot area was about 30 m wide and 80 m long. This experiment was conducted not only in order to increase the knowledge and understanding of the fire behaviour in the field but to provide data for the validation of physics based models of fire spread. In particular, the effects of wind on the geometric and thermal properties of the flame front in the field were investigated. The flame temperature along the vertical direction and the radiation emitted ahead of the flame front, were measured. The methodology employed in this experiment and some quantitative measurements of wind velocity and direction, flame geometric properties, are also presented and discussed. The measurements and observations exhibit that the behaviour of the fire and the flame structure character are very different from the one encountered at laboratory scale. These preliminary results show that large scale turbulence influence fire spread and affects the flame shape, temperature and radiation emission.

Seasonal mean pressure reconstruction for the North Atlantic (1750–1850) based on early marine data

Abstract. Measurements of wind strength and direction abstracted from European ships' logbooks during the recently finished CLIWOC project have been used to produce the first gridded Sea Level Pressure (SLP) reconstruction for the 1750–1850 period over the North Atlantic based solely on marine data. The reconstruction is based on a spatial regression analysis calibrated by using data taken from the ICOADS database. An objective methodology has been developed to select the optimal calibration period and spatial domain of the reconstruction by testing several thousands of possible models. The finally selected area, limited by the performance of the regression equations and by the availability of data, covers the region between 28° N and 52° N close to the European coast and between 28° N and 44° N in the open Ocean. The results provide a direct measure of the strength and extension of the Azores High during the 101 years of the study period. The comparison with the recent land-based SLP reconstruction by Luterbacher et al. (2002) indicates the presence of a common signal. The interannual variability of the CLIWOC reconstructions is rather high due to the current scarcity of abstracted wind data in the areas with best response in the regression. Guidelines are proposed to optimize the efficiency of future abstraction work.