Diurnal Variations In Wind Speed Research Articles

Evaluation of the Wind Shear at a Site in the North-West of the Yucatan Peninsula, Mexico

Extrapolations from 10m above the ground up to the wind turbine hub height are frequently made to the data available for wind power assessments. Because of its simplicity, the power law profile has been one of the most popular mathematical formulations to predict the vertical wind shear. This paper presents an analysis of wind speed and wind shear in terms of the directional, diurnal and seasonal patterns for a site at the Autonomous University of Yucatan which experiences the tropical conditions of the Yucatan Peninsula in Mexico. This analysis takes a detailed look at frequency distributions to facilitate a comprehensive understanding of the local climatic conditions. Diurnal wind speed variations are shown to be affected in particular by the differing wind conditions associated with fetches over two distinct offshore regions. Seasonal behaviour suggests some departure from the oscillations expected from temperature variation. In addition, the use of rate of change of temperature at one height is proposed as an alternative to vertical temperature gradient inferred from two heights as an indicator of atmospheric stability which will affect the wind shear. The work presented is part of a regionally funded research program to evaluate the onshore and offshore wind potential in the north of the Yucatan Peninsula.

An Evaluation of Two NEXRAD Wind Retrieval Methodologies and Their Use in Atmospheric Dispersion Models

Abstract Two entirely different methods for retrieving 3D fields of horizontal winds from Next Generation Weather Radar (NEXRAD) radial velocities have been evaluated using radar wind profiler measurements to determine whether routine wind retrievals would be useful for atmospheric dispersion model applications. The first method uses a physical algorithm based on four-dimensional variational data assimilation, and the second simpler method uses a statistical technique based on an analytic formulation of the background error covariance. Both methods can be run in near–real time, but the simpler method was executed about 2.5 times as fast as the four-dimensional variational method. The observed multiday and diurnal variations in wind speed and direction were reproduced by both methods below ∼1.5 km above the ground in the vicinity of Oklahoma City, Oklahoma, during July 2003. However, wind retrievals overestimated the strength of the nighttime low-level jet by as much as 65%. The wind speeds and directions obtained from both methods were usually similar when compared with profiler measurements, and neither method outperformed the other statistically. Within a dispersion model framework, the 3D wind fields and transport patterns were often better represented when the wind retrievals were included along with operational data. Despite uncertainties in the wind speed and direction obtained from the wind retrievals that are higher than those from remote sensing radar wind profilers, the inclusion of the wind retrievals is likely to produce more realistic temporal variations in the winds aloft than would be obtained by interpolation using the available radiosondes, especially during rapidly changing synoptic- and mesoscale conditions.

Wind resource assessment of eastern coastal region of Saudi Arabia

Depleting oil and gas reserves, combined with growing concerns of global warming, have made it inevitable to seek energy from renewable energy sources such as wind. The utilization of energy from wind is becoming increasingly attractive and is being widely used/disseminated for substitution of oil-produced energy, and eventually to minimize atmospheric degradation. Quantitative assessment of wind resource is an important driving element in successful establishment of a wind farm/park at a given location. More often than not, windenergy resources are relatively better along coastlines. In the present study, hourly mean wind-speed data of the period 1986–1997 recorded at the solar radiation and meteorological station, Dhahran (26°32′ N, 50°13′ E, eastern coastal plain of Saudi Arabia), have been analyzed to present different characteristics of wind speed in considerable depth such as: yearly, monthly, diurnal variations of wind speed, etc. The long-term monthly average wind speeds for Dhahran range from 4.2–6.4 m/s. More importantly, the study deals with impact of hub height on wind energy generation. Attention has also been focussed on monthly average daily energy generation from different sizes of commercially available wind machines (150, 250, 600 kW) to identify optimum wind machine size from energy production point of view. It has been found that for a given 6 MW wind farm size, at 50 m hub height, cluster of 150 kW wind machines yields about 48% more energy as compared to 600 kW wind machines. Literature shows that commercial/residential buildings in Saudi Arabia consume an estimated 10–40% of the total electric energy generated. So, concurrently, as a case study, attempt has been made to investigate/examine the potential of utilizing hybrid (wind+diesel) energy conversion systems to meet the load requirements of hundred typical 2-bedroom residential buildings (with annual electrical energy demand of 3512 MWh). The hybrid systems considered in the present case-study consist of different combinations of wind machines (of various capacities), supplemented with battery storage and diesel back-up. The deficit energy generated from the back-up diesel generator and the number of operational hours of the diesel system to meet a specific annual electrical energy demand of 3512 MWh have also been presented. The diesel back-up system is operated at times when the power generated from wind energy conversion systems (WECS) fails to satisfy the load and when the battery storage is depleted. The evaluation of hybrid system shows that with seven 150 kW WECS and three days of battery storage, the diesel back-up system has to provide 17.5% of the load demand. However, in absence of battery storage, about 37% of the load needs to be provided by the diesel system.

Investigation of wind characteristics and assessment of wind energy potential for Waterloo region, Canada

Abstract Wind energy becomes more and more attractive as one of the clean renewable energy resources. Knowledge of the wind characteristics is of great importance in the exploitation of wind energy resources for a site. It is essential in designing or selecting a wind energy conversion system for any application. This study examines the wind characteristics for the Waterloo region in Canada based on a data source measured at an elevation 10 m above the ground level over a 5-year period (1999–2003) with the emphasis on the suitability for wind energy technology applications. Characteristics such as annual, seasonal, monthly and diurnal wind speed variations and wind direction variations are examined. Wind speed data reveal that the windy months in Waterloo are from November to April, defined as the Cold Season in this study, with February being the windiest month. It is helpful that the high heating demand in the Cold Season coincides with the windy season. Analysis shows that the day time is the windy time, with 2 p.m. in the afternoon being the windiest moment. Moreover, a model derived from the maximum entropy principle (MEP) is applied to determine the diurnal, monthly, seasonal and yearly wind speed frequency distributions, and the corresponding Lagrangian parameters are determined. Based on these wind speed distributions, this study quantifies the available wind energy potential to provide practical information for the application of wind energy in this area. The yearly average wind power density is 105 W/m2. The day and night time wind power density in the Cold Season is 180 and 111 W/m2, respectively.

A Case Study of the Great Plains Low-Level Jet Using Wind Profiler Network Data and a High-Resolution Mesoscale Model

Abstract A detailed case study of one complete episode of a typical summertime Great Plains low-level jet (LLJ) using data collected by the NOAA wind profiler demonstration network is presented. The high temporal and spatial resolution of the data from the profiler network permits a much more detailed picture of the Great Plains LLJ than is possible from previous studies of this phenomenon. A three-dimensional mesoscale numerical model is also used to simulate the episode and to provide information on the physical mechanisms responsible for the initiation, evolution, maintenance, and decay of the LLJ. The position and width of the jet core, as well as the diurnal variation of wind speed and direction inside the jet core are well predicted by the model. The analysis and modeling suggest that the diurnal oscillation of horizontal pressure gradient over sloping terrain is secondary to the inertial oscillation mechanism resulting from the release of frictional constraint in the evening and throughout the nigh...

Simulating sulfur dioxide plume dispersion and subsequent deposition downwind from a stationary point source: A model

Dispersion and subsequent deposition of SO 2 downwind from a stationary point source are affected by several transport processes: buoyancy at the source, advection, and air turbulence en route from the source to the area of impact. In this paper, SO 2 transport processes are simulated by way of Lagrangian air parcel trajectory simulations. In these simulations, the source releases air parcels in puffs. The calculations cover both daytime and night-time conditions and take into account: (i) solar geometry, (ii) diurnal variations of wind speed and air turbulence, (iii) resistance to the transfer of SO 2 from the air to the land, and (iv) flat terrain. Deposition to the forest is determined by calculating the rate of SO 2 flux from individual air parcels to the land according to the parcel's velocity and an assumed air-to-surface SO 2 transfer coefficient. Daily cumulative SO 2 deposition rates are calculated by summing the simulated diffusional fluxes of SO 2 from air to land over each simulated time step. Daily cumulative SO 2 amounts are calculated for downwind distances from 0 to 42 km, for smokestack heights from 30 to 200 m, and for each day of the year according to historical year-round and local weather patterns representative of days with neutral conditions and days with transitions from stable to unstable conditions. Annual per hectare rates of SO 2 deposition are calculated by way of Monte Carlo simulations, according to historical patterns for daily wind, atmospheric stability, and precipitation. These simulations are calibrated for the area surrounding a coal-burning power generator at Grand Lake in south-central New Brunswick, Canada. Calculated concentrations for SO 2 were similar to those obtained with a mobile SO 2 detection unit and a SO 2-monitoring unit 42 km NE from the emission source. Cumulative SO 2 deposition rates were reasonably similar to those obtained with PbO 2 sulfation plates. A detailed comparison revealed topography was an important factor in modifying actual cumulative SO 2 deposition rates.

Wind power in Jamaica

Parameters to evaluate the potential for using wind energy to generate electricity in Jamaica were obtained. These include the average wind power scaled to a height of 20 m at existing weather stations and temporary anemometer sites, the variation in annual and monthly wind power, and the frequency distribution of wind speed and wind energy available. Four small commercial turbines were assumed to be operating at some of the sites, and the estimated energy captured by them, the time they operated above their cut-in speed and their capacity factors were also determined. Diurnal variations of wind speed and prevailing wind directions are discussed and a map showing wind power at various sites was produced. Two stations with long-term averages, Manley and Morant Point, gave results which warranted further investigation. Results from some temporary stations are also encouraging. Mean wind speeds at two other sites in the Caribbean are given for comparison. A method for estimating the power exponent for scaling the wind speed from climatic data is described in Appendix 2.

Diurnal variations of wind speeds at a shortgrass prairie site — a model

Comparison of the mean monthly diurnal variation of wind speed and air temperature (2 m) shows that they have the same pattern and that these patterns change seasonally in the same manner. A model for stimulated diurnal variation in air temperature was used to represent diurnal variations of surface wind speeds at a shortgrass prairie site. Inputs for the model are latitude, Julian date and daily wind travel. The important assumptions for the model are (1) the maximum wind speed occurs during the afternoon period, (2) the minimum wind speed occurs sometime around sunrise, (3) during the day the wind speeds can be described with a truncated sine function, and (4) during the night the wind speeds can be described with an exponential function. Reasonable approximations of long-term hourly mean diurnal variations in wind speed were simulated; however, the model was less accurate for individual days. The wind speed model has potential application in estimating wind statistics when wind power calculations are required, and as abiotic data input for research and application models.

Winds between San Diego and San Clemente Island

Dense ship observations off San Diego were used to capture the diurnal and seasonal wind trends. The land breeze regime extends to 40 km off San Diego in the winter, but goes to less than 10 km when averaged for the winter. Significant diurnal variations in wind speed occur in all seasons from the coast to beyond 140 km. Ship observations were averaged over 0.2° of latitude and longitude. These have significant structure that is obscured in other studies based upon 1° averages. Wind speeds decrease by a factor of 2 or more from 140 km offshore to the coast in both the northerly and westerly component. The mean flow has a weak summer southerly component. This is in opposition to earlier studies which indicated northerly mean monthly flow all year. Ship observations were compared to San Diego Airport and San Clemente Island measurements in order to check the accuracy of allowing land measurements to substitute for over water measurements. San Diego winds were found to be very representative of the nearest 10 km of ocean in wind speed and direction on the diurnal and seasonal scales. San Diego would be a good proxy station from which to infer the long‐term near shore meteorlogical conditions. San Clemente Island wind speeds are systematically less than the ship observed wind speeds in the easterly component. But the correspondence between the northerly component at San Clemente and ships is irregular in the diurnal and monthly means. This station could not be used to infer the northerly component without an uncertain and elaborate correction.

Sensitivity of particle deposition to changes in deposition velocity

A simple two-dimensional numerical model is used to study the sensitivity of particle deposition to changes in deposition velocity. Diurnal variations in wind speed, stability and surface resistance are considered. For the relatively small values of deposition velocity normally attributed to small particles, it was found that depletion of material exhibits a strong dependence upon the magnitude of the deposition velocity and the cycle of stabilities encountered. These results are in contrast to some other findings valid for small surface resistance values.

Atmospheric turbulence

AbstractEvidence which has accumulated shows that the classical theory of atmospheric turbulence which assumes that K the coefficient of eddy diffusion is constant with height is inadequate to explain the observed variations of wind and temperature with height. It was shown however by the present writer, 1946, that if K could be represented by a certain power law of the height above the surface it was possible to account for many of the complicated problems of atmospheric diffusion near the earth's surface. In the present paper it is shown that with this power law representation of K it is possible to give a quantitative treatment of the approach of the surface wind to the geostrophic wind. The angle of veer between the surface wind and the isobars is found to be independent of the roughness of the surface and to be dependent only upon the stability. The diurnal variation of wind speed and direction at various heights is discussed on the basis of the present theory and is shown to be in accordance with observations.