Meteorological Mast Research Articles

Near surface spatially averaged air temperature and wind speed determined by acoustic travel time tomography

Acoustic travel time tomography is presented as a possibility for remote monitoring of near surface air temperature and wind fields. This technique provides line-averaged effective sound speeds changing with temporally and spatially variable air temperature and wind vector. The effective sound speed is derived from the travel times of sound signals which propagate at defined paths between different acoustic sources and receivers. Starting with the travel time data a tomographic algorithm (Simultaneous Iterative Reconstruction Technique, SIRT) is used to calculate area-averaged air temperature and wind speed. The accuracy of the experimental method and the tomographic inversion algorithm is exemplarily demonstrated for one day without remarkable differences in the horizontal temperature field, determined by independent in situ measurements at different points within the measuring field. The differences between the conventionally determined air temperature (point measurement) and the air temperature determined by tomography (area-averaged measurement representative for the area of the measuring field 200 m x 260 m) were below 0.5 K for an average time of 10 minutes. The differences obtained between the wind speed measured at a meteorological mast and calculated from acoustic measurements are not higher than 0.5 m s -1 for the same averaging time. The tomographically determined area-averaged distribution of air temperature (resolution 50 m x 50 m) can be used to estimate the horizontal gradient of air temperature as a pre-condition to detect horizontal turbulent fluxes of sensible heat.

Evaluation of inversion strengths and mixing heights during extremely stable atmospheric stratification

We have compiled data from Finnish sounding stations and classified the inversions according to their total depth and the stability of the boundary layer. We studied the persistence of the inversions and the influence of cloudiness and wind speed on the temperature gradient. Additionally, we addressed the specific problems of an urban area, using measurements from a meteorological mast situated in the Helsinki metropolitan area and comparing them to those from the radiosonde profiles at the rural site of Jokioinen. We also compared several common schemes for the height of the stable boundary layer to results from our own Finnish Meteorological Institute (FMI) method. Based on this analysis a modification to the FMI method was suggested.

On sonic anemometer measurement theory

In this paper a model for the measuring process of sonic anemometers (ultrasound pulse based) is presented. The differential equations that describe the travel of ultrasound pulses are solved in the general case of non-steady, non-uniform atmospheric flow field. The concepts of instantaneous line-average and travelling pulse-referenced average are established and employed to explain and calculate the differences between the measured turbulent speed (travelling pulse-referenced average) and the line-averaged one. The limit k 1 l=1 established by Kaimal in 1968, as the maximum value which permits the neglect of the influence of the sonic measuring process on the measurement of turbulent components is reviewed here. Three particular measurement cases are analysed: A non-steady, uniform flow speed field, a steady, non-uniform flow speed field and finally an atmospheric flow speed field. In the first case, for a harmonic time-dependent flow field, Mach number, M (flow speed to sound speed ratio) and time delay between pulses have revealed themselves to be important parameters in the behaviour of sonic anemometers, within the range of operation. The second case demonstrates how the spatial non-uniformity of the flow speed field leads to an influence of the finite transit time of the pulses ( M≠0) even in the absence of non-steady behaviour of the wind speed. In the last case, a model of the influence of the sonic anemometer processes on the measurement of wind speed spectral characteristics is presented. The new solution is compared to the line-averaging models existing in the literature. Mach number and time delay significantly distort the measurement in the normal operational range. Classical line averaging solutions are recovered when Mach number and time delay between pulses go to zero in the new proposed model. The results obtained from the mathematical model have been applied to the calculation of errors in different configurations of practical interest, such as an anemometer located on a meteorological mast and the transfer function of a sensor in an atmospheric wind. The expressions obtained can be also applied to determine the quality requirements of the flow in a wind tunnel used for ultrasonic anemometer calibrations.

Stable Atmospheric Boundary-Layer Experiment in Spain (SABLES 98): A Report

This paper describes the Stable Atmospheric Boundary Layer Experiment in Spain (SABLES 98), which took place over the northern Spanish plateau comprising relatively flat grass- land, in September 1998. The main objectives of the campaign were to study the properties of the mid-latitude stable boundary layer (SBL). Instrumentation deployed on two meteorological masts (of heights 10 m and 100 m) included five sonic anemometers, 15 thermocouples, five cup anemometers and three propeller anemometers, humidity sensors and radiometers. A Sensitron mini-sodar and a tethered balloon were also operated continuously. A triangular array of cup anemometers was installed to allow the detection of wave events. Two nocturnal periods analysed on 14-15 and 20-21 September are used to illustrate the wide-ranging characteristics of the SBL.

Wind energy surveying and technoeconomic assessment of identifiable WEC system installations

There are several areas with high wind energy potential in Greece. The Thrace region is one of the least explored areas concerning this wind potential. This paper presents the results of a preliminary evaluation of the Eastern Macedonia — Thrace/Greece wind energy resource. For this purpose, wind measurements from two local weather stations were obtained and a supplementary meteorological mast was installed at a selected location. The availability of such data was sufficient, and the WAsP model was used to evaluate them. Several potential sites, appropriate for wind energy conversion system (WECS) installations, were selected and investigated. A method of evaluating the economic feasibility of the required private investments on WECS installations is presented. Such privately owned generation systems may or may not operate in parallel with a large scale network, thus the energy produced by it is either provided to meet local load needs or transmitted to the external grid system. The paper also assesses non-financial attributes, typically associated with the implementation of WECS installations, such as local/national environmental and socio-economic impacts. A general computer program has been developed, aiming to become a flexible computational tool for investigating possible sites with wind potential. The program also takes into account the specific technoeconomical constraints pertaining to Greek reality by following the latest national development and energy laws applicable to the production by private entrepreneurs of electrical energy from renewable energy sources, which is sold to the Greek Public Power Corporation (P.P.C.). To make good use of the program, several potential sites and a case of a local industry in the geographical area of Thrace/Greece are thoroughly analyzed, and the pertinent results are presented.

The Mast on the House

An often encountered problem when preparing the basic input data for a wind atlas study is the correction for the influence of the house or hut on which the mast—whose data form the basis of this wind atlas—is placed. The article will describe an experiment where this problem has been addressed. The knowledge gained will be used to give guidelines as to the use of the WAsP program to correct the observations. Should the house/hut simply be treated as an extension of the mast, should the house/hut be treated as a hill with speed-up effects, or should the house/hill be ignored completely? The paper will show that the house/hut should indeed be treated as a hill with speed-up effects. Placing meteorological masts on houses or huts is common practice in quite a few countries in the world. The problem is therefore one which most people involved in detailed wind resource assessment will face sooner or later. The article will show that the effect of the house/hut is such that it cannot be ignored. Copyright © 2001 John Wiley & Sons, Ltd.

The Mast on the House

An often encountered problem when preparing the basic input data for a wind atlas study is the correction for the influence of the house or hut on which the mast—whose data form the basis of this wind atlas—is placed. The article will describe an experiment where this problem has been addressed. The knowledge gained will be used to give guidelines as to the use of the WAsP program to correct the observations. Should the house/hut simply be treated as an extension of the mast, should the house/hut be treated as a hill with speed-up effects, or should the house/hill be ignored completely? The paper will show that the house/hut should indeed be treated as a hill with speed-up effects. Placing meteorological masts on houses or huts is common practice in quite a few countries in the world. The problem is therefore one which most people involved in detailed wind resource assessment will face sooner or later. The article will show that the effect of the house/hut is such that it cannot be ignored. Copyright © 2001 John Wiley & Sons, Ltd.

Chemical and mineralogical composition of solid fraction of ambient aerosol at different levels (Kopisty near Most, NW Bohemia)

The dependence of the chemical and mineralogical composition of solid fraction of aerosols on the sampling height was studied using a meteorological mast located in a highly industrialized region of the Czech Republic. The aerosol was collected at an altitude of 2, 20, 40, 60 and 80 m above the earth's surface using a high-volume impactor capable of sampling all the particles with a diameter greater than 0.5 μm. The contents of seven identified minerals indicated that the concentration of soil minerals in the solid fraction of aerosol decreases sharply with altitude, whereas the proportion of fly ash emitted by coal-powered power plants in the region increases with altitude. The lowest concentration of aerosol was found at a sampling height of 40 m.

Influence of the Meteorology Mast on a Cup Anemometer

The actuator disc model is applied on lattice-type meteorological masts to estimate the influence of the tower on the accuracy of the measured wind speed. Combining the results with corrections for the boom, on which the anemometer is mounted, good agreement is found for measurements made on the mast at Tjœcereborg. Iso-speed plots are computed to estimate the influence of different solidities. Depending on the distance from the mast and the solidity the influence from a typical mast is normally less than 3%.

Photochemical air pollution characteristics at the station of the NCSR-Demokritos, during the MEDCAPHOT-TRACE campaign in Athens, Greece (20 August–20 September 1994)

In this paper the continuous meteorological and air pollution measurements collected at the station of the NCSR-Demokritos during the MEDCAPHOT-TRACE campaign (20 August–20 September 1994) are presented and discussed. The station site is located about 10 km east from the center of Athens at 280 m altitude. The air pollution species measured were O 3, NO, NO 2 and SO 2 while the meteorological parameters were recorded on a 84 m high meteorological mast. Ozone values up to 180 ppb have been measured during pollution episodes. The maximum hourly average ozone mixing ratio from the western sector (urban) is about 50 ppb higher than the corresponding value of the NE sector (rural). At the same time the average ozone rate of increase during the morning hours was about 20 ppb h -1 and the typical wind speeds from 3 to 4 m s -1. The creation of this excess ozone amount is mainly attributed to the daily photochemistry. In the air masses coming from all wind directions comparable nighttime levels of O x (NO 2+O 3) around 65 ppb are observed while the ozone and nitrogen dioxide values are clearly anticorrelated. The observed mixing ratios coming from the NE rural sector vary between 50 and 80 ppb and they are almost indifferent of the wind speed. For wind speeds higher than 7 m s -1 the average ozone value was 68±7 ppb (1.8 ppb for nitrogen dioxide). Such ozone levels despite the altitude of our station (280 m above sea level) are considered as high rural concentrations, if they are compared with similar values in Central Europe.

Ozone deposition in relation to canopy physiology in a mixed conifer forest in Denmark

In this study CO 2 and H 2O flux measurements made above a spruce forest was compared with the ozone flux to the canopy during growing seson 1995. The fluxes were determined by micro meteorological gradient methods using a 36-m tall meteorological mast. The trees were about 12 m high and air sampling was done from 36 and 18 m. The preliminary results suggest that there is only little correlation between ozone concentration in 36 m and the ozone flux to the forest, but the diurnal pattern of ozone uptake seems to be significantly influence by stomatal conductance. The cumulative total ozone uptake seems to follow very well the evapotranspiration.

Study on the Wind Measurements and Performance Evaluation of a WTGS in Complex Terrain. 1st Report. Evaluation of NEDO-500kW WTGS at Tappi Wind Park.

As the use of wind turbine generator system (WTGS) expand over the world, complex terrain has become the site-candidates more often. Therefore, Complex Terrain is now one of the keen issues, which however, has been the original problem in a mountainous country such as Japan. International Electrotechnical Commission (IEC) is now actively preparing a standard entitled Power Performance Measurement, which describes the procedure of measuring performance of a wind turbine generator system. However, the standard is applicable to WTGS built on rather flat open areas in principle and is hardly applicable to WTGS in complex terrain. This has been well recognized, but it is the opinion of the majority of the IEC working group that understandings and technique for power performance measurement of a WTGS in complex terrain is still under development. Therefore, a new and more reliable method of performance measurement of a WTGS in complex terrain is required not only from the technical aspects but also from economics. The particular purpose of the present work is to measure and evaluate the wind speed and power performance of the national 500 kW research WTGS, while the generalized purposes are : (1) to develop a reliable method of wind speed measurement and (2) to develop a reliable method of power performance measurement of a WTGS in complex terrain. In this work, firstly, the measured wind data in typical complex terrain such as Tappi wind-park are analyzed. Secondly, a new method of performance measurement/analysis is discussed. Method of bin is applied for data analysis, while a reference meteorological mast and reference factors are newly introduced. Finally, the new method is evaluated.

Evaluation of minisodar performance operating in high wind conditions

The performance of a high resolution tristatic minisodar is evaluated over an area of complex topography using a 30m high meteorological mast equipped with cup anemometers and bivanes. The instrumentation was in operation at the Moni Toplou Wind Park (Island of Crete, Greece) and the comparison covered a range of high wind speed and different meteorological conditions during day and night-time periods. The Sodar measurements of mean wind speed and direction for 15 min time segments agreed with the in situ measurements although an underestimation of the wind speed is evident. On the other hand the standard deviations of the wind speed and direction as estimated by Sodar gave poor agreement with the in situ instrumentation.

Observation of a nonlinear wave disturbance in the marine atmosphere by the synthetic aperture radar aboard the ERS 1 satellite

A nonlinear wave disturbance in the marine atmosphere associated with an atmospheric cold front has been identified on a spaceborne radar image of the North Sea by its imprint on the sea surface. This nonlinear wave disturbance is either a solitary wave disturbance or an undular bore propagating in the lower marine atmosphere. The radar image showing sea surface manifestations of this atmospheric wave disturbance was acquired over the North Sea by the synthetic aperture radar (SAR) aboard the first European Remote Sensing Satellite ERS 1 on March 8, 1992. Atmospheric waves become visible on radar images of the sea surface because they are associated with a varying wind field at the sea surface, which modulates the sea surface roughness, and, thus, the backscattered radar power. The identification of the wave pattern visible on the ERS 1 SAR image as a sea surface manifestation of an atmospheric nonlinear wave disturbance has been possible because this disturbance was also captured by meteorological sensors mounted on an 80‐m high meteorological mast located on the island of Heligoland. Geophysical parameters characterizing the atmospheric wave disturbance are derived from the ERS 1 SAR image and from the in situ meteorological data. The wave period in the reference frame moving with the average wind is 9.5 min, the average wavelength is 2300 m, and the propagation velocity is 4.5–4.9 m s−1. Estimates of the amplitude of the wind speed fluctuations in the wave propagation direction derived from the meteorological measurements at Heligoland and from the gray level variations in the SAR image yield values between 1.3 and 3.0 m s−1. The experimental data are interpreted in terms of theories of atmospheric nonlinear gravity waves.

Short-term prediction of local wind conditions

Using Numerical Weather Prediction (NWP) models it has been shown that they, combined with models (either physical or statistical) taking local effects into account, can be used to predict the wind locally better than the models commonly used today (as eg persistence). By “local” is meant at one distinct spot, as eg the location of a meteorological mast. The physical model of local effects takes the following into account: shelter from near-by obstacles, the effect of roughness changes and the effect of the local orography. The large-scale flow is linked to the surface flow by the geostrophic drag law, and the logarithmic wind profile. The predictions are made up to 36 hours ahead. The model is tested on data from 50 meteorological stations scattered all over Europe.

A one dimensional wind model for diffusion calculations

A simple one dimensional wind model, designed for diffusion calculations in flat environments with obstructions, is proposed. It covers the surface layer and up to a maximum height of 500 m with three levels. The lowest level is the internal boundary layer, in which the influence of the immediate environment is manifest. The second is the surface layer in which the wind profile is characterized by the fetch conditions further upstream. The third is the spiral layer, where the wind turns with height. The actual depth of the surface layer is estimated by the model. In both the surface layer and the internal boundary layer, Monin-Obukhov theory is applied. The spiral layer is represented by a classical Ekman-Taylor solution matched at the top of the surface layer. This conceptual model is then tested with data from a meteorological mast at Garching (near Munich, Germany).

Gust modelling for wind loading

In this paper the TNO gust analysis method and the resulting TNO gust model are described. The method has been applied to a set of 700 hours of stationary wind speed time series measured at the meteorological mast at Cabauw, The Netherlands. The results are discussed in this paper. The TNO gust model has been developed for the calculation of wind turbine loads, especially fatigue loads. To model gusts an analysis method has been developed to statistically analyze full-scale wind speed data and translate these to discrete gusts. The main result of the TNO gust model is that finally, all gust amplitudes are described by one single expression being a function of the height, the mean wind speed, the turbulence intensity, the gust duration and the probability exceedance level within an error band of less than 5%. The model also gives a relation between the gust duration and the frequency of occurence of the gusts. The TNO gust model has been incorporated in the Dutch Handbook ‘Wind Data for Wind Turbine Design’. Verification of this handbook has been performed by comparing the flap and lag loads on the blade root of three different wind turbines by means of the Handbook with the loads measured. The comparison showed very good agreement especially in the range 10 2 to 10 8 load fluctuations per year.

The climate of extreme winds at the great belt, Denmark

A study is undertaken of the extreme mean wind climate at the Great Belt, Denmark. The data material consists of a 9 year record of consecutive 10 min. averages of wind speed obtained from the meteorological mast on the island of Sprogø in the middle of the Great Belt.Two principal methods of extreme data abstraction are introduced namely the Peak-Over-Threshold (POT) method and the Annual Maximum (AM) method. Various statistical models have been applied both to the POT- and the AM-series data to investigate model behaviour for upper quantile estimates including assessment of uncertainty of these estimates. The applicability of the two methods is assessed and a recommendation is given for the most suitable method when dealing with short-term records (< 10 years).Finally, a comparison is made with adjusted extreme wind speed data from another meteorological site in Denmark.

Measurements of wind induced vibrations of a full-scale steel chimney

Wind-induced vibrations and wind pressures have been measured on a full-scale experimental steel chimney with a height of 28 m and a diameter of 0.91 m at the test field of the University of Aachen, Germany. The wind characteristics at the site have been measured at four levels on a meteorological mast standing close to the chimney. Characteristic values of the pressure distribution in respect to the drag and the lift have been analysed.For the along-wind vibration the aerodynamic admission function has been developed from the vertical coherence of the wind speed as well as from the dynamic response directly. Calculated gust response factors based on values from different sources of the literature have been compared with the measured values.The vortex-excited cross-wind response measured over three years is in good agreement with the prediction method of the author. Furthermore, it could be shown, that the interaction effect between the Strouhal frequency and the natural frequency of the chimney can produce a “new” exciting frequency which is lower than the Strouhal frequency and broadens the bandwidth of the resonance curve.

Study of the wind speed u-component spectra by using low-response instrumentation: a model comparison

A set of spectra for the wind speed u-component at 6 and 100 m heights taken by a cup-anemometer at CIBA site (Low Atmospheric Research Center, Spain) is presented. Turbulent conditions at the surface layer are evaluated by using a small meteorological mast and applying a typical profile method based on a least-squares approach over five heights. Under stable conditions, quite good agreement is obtained between observed spectra and the Olesen et al. (1984) and Kaimal et al. (1972) models for the slopes of the different regions into which stable spectra are divided. However, the spectral energy density is underestimated by the data. Also, a gap is clearly found in the low frequency range. The peak frequency is right-shifted. This shift could be explained by considering that the cup-anemometer does not sense some turbulence energy (specifically the convective part of the spectrum), but is also can be interpreted as mechanical turbulence losses due to buoyancy forces damping out the 3-dimensional eddies scaled by h, the height of the boundary layer. Under unstable conditions, the Olesen et al. (1984) model performs quite good when z i , the depth of the convective boundary layer, is evaluated by using the formulation of San José and Casanova (1988). Finally, a sensitivity test for z i is presented.