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Inherent uncertainties in meteorological parameters for wind-turbine design

Description: One of the major difficulties associated with meteorological measurements is the inability to duplicate the experimental conditions from one day to the next. This lack of consistency is compounded by the stochastic nature of many of the meteorological variables of interest. Moreover, simple relationships derived in one location may be significantly altered by topographical or synoptic differences encountered at another. The effect of such factors is a degree of inherent uncertainty if an attempt is made to describe the atmosphere in terms of universal laws. In this paper some of these uncertainties and their causes are examined, examples are presented and some implications for wind turbine design are suggested.
Date: August 1, 1981
Creator: Doran, J.C.
Partner: UNT Libraries Government Documents Department

Wind direction variations in strong winds

Description: Significant differences exist between the angular fluctuations experienced at a fixed point, averaged over a disk of rotation, and those felt by a blade element rotating about a horizontal axis. The static and dynamic descriptions of these fluctuations are an important aspect in design considerations and in the development of tracking strategies. Several methods of description and interpretation have been presented here, but further development is clearly required for a comprehensive picture of wind direction fluctuations.
Date: December 1, 1979
Creator: Doran, J. C.
Partner: UNT Libraries Government Documents Department

Some aspects of fluctuating vertical wind shears

Description: Fluctuating vertical shears of wind speed have been measured using an array of towers. The statistical distributions of these shears are compared with formulas proposed by Fichtl (1971, 1972) and good agreement is found. A comparison of Fichtl's formula for the standard deviation of the fluctuating shears with a more empirical one proposed by Ramsdell (1978) shows that the latter is consistent with the former under the proper conditions. The probability of occurrence of extreme shears in speed is discussed. Directional shears are not treated. Fluctuating shears two or more times larger than the mean values are shown to be readily obtainable, and their likelihood increases as the mean measuring height increases if ..delta..Z is held fixed.
Date: May 1, 1981
Creator: Doran, J.C.
Partner: UNT Libraries Government Documents Department

Gust characteristics for WECS design and performance analysis

Description: This document provides a description of some gust characteristics which are useful in the study of wind turbine fatigue caused by a fluctuating wind environment. The particular gust form chosen can also be used in the analysis of the dynamic response of a turbine. The statistical behavior of such gust characteristics is not identical to that determined simply from the wind recorded by an anemometer. These modes of behavior may be related, however, by the application of appropriate digital filters to the anemometer data. This procedure has been carried out for a number of sample cases, and the variations of the resultant gust features are presented. A number of suggestions on specific applications and interpretations of the data are included.
Date: May 1, 1980
Creator: Doran, J.C. & Powell, D.C.
Partner: UNT Libraries Government Documents Department

Comparison of model and observations of the wake of a MOD-OA wind turbine

Description: A series of wind velocity measurements upwind and downwind of the MOD-OA wind turbine at Clayton, New Mexico, was used to determine some of the characteristics of wakes within approximately two blade diameters of the machine. The magnitudes and shapes of the velocity profiles downwind of the turbine were compared with results obtained from a model. Generally good agreement was obtained at speeds well below the rated speed of the MOD-OA, but the results were not as satisfactory for higher values.
Date: October 1, 1982
Creator: Doran, J.C. & Packard, K.R.
Partner: UNT Libraries Government Documents Department

Simple nocturnal slope-flow data from the Rattlesnake Mountain site

Description: Detailed vertical profiles of the wind and temperture structure of nocturnal slope flows were measured at a site that is uniform in the cross-slope direction. The upper part of the slope closely approximates a simple, tilted plane. These measurements were made from three towers at different distances from the ridge crest, each of which extended through the local depth of the katabatic flow. The tower wind and temperature data from the four best cases of slope flow observed in 1980 and 1981 are listed, as well as ambient wind and temperature profiles to a height of 300m from a Tethersonde flown at the experimental site and surface winds from a network of stations surrounding the site.
Date: October 1, 1982
Creator: Horst, T.W. & Doran, J.C.
Partner: UNT Libraries Government Documents Department

An overview of the ASCOT program

Description: ASCOT (Atmospheric Studies in Complex Terrain) is a multi-laboratory U.S. Department of Energy research program studying the properties of atmospheric boundary layers over non-uniform terrain and the interactions among various scales of motion that influence those properties. Within this context, one of the principal goals of the ASCOT program is to provide information necessary for an accurate description of transport and diffusion processes for atmosphere pollutants that may be released in regions of complex terrain. Three examples from past ASCOT research relevant to this goal are presented. Current and proposed research in the Front Range region of Colorado in the vicinity of the Rocky Flats Plant is also described.
Date: September 1, 1993
Creator: Doran, J. C.
Partner: UNT Libraries Government Documents Department

Intermittent turbulence events observed with a sonic anemometer and minisodar during CASES99.

Description: The Cooperative Air Surface Exchange Study 1999 (CASES99), designed to investigate in detail the nocturnal boundary layer (NBL) of the atmosphere with particular emphasis on turbulence and turbulence events, took place during October 1999, within the Atmospheric Boundary Layer Experiments (ABLE) region east of Wichita KS. The principal measurement site was a heavily instrumented 2-km square located near Leon (LE), KS, but additional sites at Smileyberg (SM) and Beaumont (BE) were also used. The authors augmented the normal ABLE measurements at Beaumont (radar wind profiler, minisodar, 10-m meteorological tower, precipitation gauge) with a sonic anemometer mounted on the tower, 7 m above the surface. For this campaign, the minisodar data were saved in single-pulse mode with no averaging. The Beaumont site is within gently rolling rangeland used primarily for grazing. The site is on a flat plain rising gradually to the east.The Flint Hills escarpment, located approximately 2 km to the east, marks the highest point in, and the eastern boundary of, the Walnut River watershed. Although most terrain features are subtle, terrain effects on atmospheric flows are still possible, particularly in stable conditions. The intent was to observe turbulence and, hopefully, turbulence events with the sonic anemometer and minisodar. The horizontal extent of these occurrences can be studied by including the Beaumont data with those obtained at the Leon site. In this report the authors are concerned with the occurrence of intermittent turbulence.
Date: May 12, 2000
Creator: Coulter, R. L. & Doran, J. C.
Partner: UNT Libraries Government Documents Department

The coupling of synoptic and valley winds in the Tennessee Valley

Description: The interaction of winds in a valley with the winds above the valley is of interest for both practical and theoretical reasons. For example, the forecasting of conditions affecting air quality,, emergency preparedness, or aerial spraying of pesticides requires the ability to relate local valley circulations to ambient synoptic conditions. While empirically derived relationships may be useful, it is also desirable to develop an understanding of the mechanisms responsible for the observed behavior. In this paper we combine results from analyses of measurements and model-generated data to provide insight into factors affecting the climatology of the winds in the Tennessee Valley. We discuss four mechanisms that can determine the behavior of winds in a valley. The conditions can be illustrated in terms of the expected joint frequency distributions of the surface and geostrophic winds.
Date: September 1, 1992
Creator: Doran, J.C. & Whiteman, C.D.
Partner: UNT Libraries Government Documents Department

On the development of boundary layer secondary circulations resulting from horizontally varying surface heat flux

Description: During the last decade there has been a surge in efforts to understand the processes at work in the inhomogeneous atmospheric boundary layer. Much of the interest in the problem has been driven by increasingly urgent needs to develop accurate assessments of man`s Contribution to climate change. It has been argued that subgrid-scale secondary circulations in the boundary layer can cause significant errors in parameterized turbulent surface fluxes. Such circulations -- variously termed ``inland breezes``, ``lake breezes``, ``snow breezes``, or ``nonclassical mesoscale circulations`` are becoming widely discussed and modeled. Because surface fluxes are part of the lower boundary condition for global climate models, it is important to understand when these circulations occur and what their effects are on overall turbulent transfer. What are not yet clear are the combinations of the ambient wind and the horizontal scale and intensity of surface flux variability under which we may expect boundary layer secondary circulations to occur. Several authors have modeled the development of these circulations for ad hoc situations of alternating surface characteristics, and SA have developed one parameterization relating the scale of surface heat flux variability and the ambient wind to the evolution of NCMCs. In this paper we present observations, collected in a region of inhomogeneous surface fluxes, that suggest the development of a ``farm breeze``, and we develop an alternative scaling argument to that of SA that better represents our measurement conditions.
Date: March 1, 1994
Creator: Shaw, W. J. & Doran, J. C.
Partner: UNT Libraries Government Documents Department

An experimental and numerical study of boundary layer structure over areas of inhomogeneous sensible heat fluxes

Description: In June of 1992 a boundary-layer experiment was carried out near Boardman, Oregon. The campaigns were part of a program of studies under the auspices of the US Department of Energy`s Atmospheric Radiation Measurement (ARM) program, whose goal is to improve the treatment of radiative transfer, particularly as affected by clouds, in general circulation models (GCMs) used for climate studies. One aspect of this program is concerned with the determination of appropriate lower boundary conditions for such models and the representation of subgrid-scale variability in regions where the surface conditions are not uniform. To study this problem, boundary-layer and surface properties were measured over a region of two sharply contrasting land types: a large, dry, sagebrush steppe area and irrigated farmland that formed the east, northeast, and western borders of the steppe. A combination of surface flux instrumentation, airsondes, sodars, and near-surface wind and temperature sensors was used. Measurements were carried out over the eastern portion of this region, which featured a well-defined boundary between the dry and irrigated areas. In this paper, the authors present some results from those observations and from a set of numerical simulations that address the effects of inhomogeneous surface fluxes on boundary-layer structure.
Date: March 1, 1994
Creator: Zhong, S. & Doran, J. C.
Partner: UNT Libraries Government Documents Department

An experimental and numerical study of the modifications of mixed-layer structure by inhomogeneous surface fluxes and secondary circulations

Description: The problem of scale interactions in the planetary boundary layer (PBL), i.e., how forcing mechanisms of differing spatial and temporal scales affect the properties of the PBL, has been a subject of considerable interest for some time. One aspect of this problem that has received increasing attention in recent years is the representation, in mesoscale and general circulation models. of the effects of subgrid-scale inhomogeneities in surface properties. Differences in sensible and latent heat fluxes between adjacent areas can result in secondary circulations. modifications to the boundary layer structure, and the transport of heat and moisture from one area to another. Despite their potential included on local PBL properties, such effects can not be resolved by numerical models whose scale is too coarse; thus, suitable parameterizations that account for these phenomena are needed. In this paper the authors present some results of wind and temperature measurements over an area with significant variations in surface fluxes on scales of O(10 km). They then use fine resolution numerical simulations to show how synoptic, topographical, and thermal forcing combine to affect the properties of the PBL in the region. Specifically, they consider the relative importance of topography and land-use differences on the generation of secondary circulations and on the depth of the mixed layer, and they show how these effects are modified by synoptic wind fields. Implications for coarser resolution models are also discussed.
Date: July 1, 1994
Creator: Zhong, S. & Doran, J. C.
Partner: UNT Libraries Government Documents Department

Cloud Optical Depths and Liquid Water Paths at the NSA CART

Description: Cloud optical depths have been measured using multifilter rotating shadowband radiometers (MFRSRs) at Barrow and Atqasuk, and liquid water paths have been measured at Barrow using a microwave radiometer (MWR) during the warm season (June-September) in 1999. Comparisons have been made between these quantities and the corresponding ones determined from the ECMWF GCM. Hour-by-hour comparisons of cloud optical depths show considerable scatter. The scatter is reduced, but is still substantial, when the averaging period is increased to ''daily'' averages, i.e., the time period each day over which the MFRSR can make measurements. This period varied between 18 hours in June and 6 hours in September. Preliminary results indicate that, for measured cloud optical depths less than approximately 25, the ECMWF has a low bias in its predictions, consistent with a low bias in predicted liquid water path. Based on a more limited set of data, the optical depths at Atqasuk were found to be generally lower than those at Barrow, a trend at least qualitatively captured by the ECMWF model. Analyses to identify the cause of the biases and the considerable scatter in the predictions are continuing.
Date: March 14, 2000
Creator: Doran, J. C.; Barnard, James C.; Zhong, Shiyuan & Jakob, C J.
Partner: UNT Libraries Government Documents Department

Accuracy of wind power estimates

Description: Several aspects of power estimation techniques for wind energy conversion systems are studied. The sampling rate at which data are collected, ranging from once every 2 minutes to once every 3 hours, does not appear to significantly affect the average power for recording periods of one season. Increased averaging times produce small underestimates (less than 10 percent) of available power. The Rayleigh and Weibull distributions both give poor estimates of power for low mean wind speed situations, with the former being significantly worse. At higher wind speeds, both give good estimates, and the Rayleigh distribution is considerably simpler in form and application. A height extrapolation scheme for Weibull parameters is also investigated. Results are satisfactory for power estimates of ensembles of machines, but the scatter of values about the mean makes the method inappropriate for individual cases.
Date: October 1, 1977
Creator: Doran, J.C.; Bates, J.A.; Liddell, P.J. & Fox, T.D.
Partner: UNT Libraries Government Documents Department

Effects of mesoscale surface inhomogeneities on atmospheric boundary layer transfer

Description: Defining the nature of turbulent transfer over horizontally inhomogeneous surfaces remains one of the challenges in meteorology. Because the transfer of energy and momentum through the atmospheric boundary layer forms part of the lower boundary condition for global climate models (GCMs), the problem is important. Over the last two decades, advances in sensor and computer technology wave made good point measurements of turbulent fluxes fairly routine. A fundamental question with respect to climate models, however, is how such point measurements are related to average fluxes over the area of a GCM grid box. In this paper we will use data from the field program to depict the evolution of the boundary layer over adjacent, sharply contrasting surface types on two separate occasions. We will then use simple scaling based on the observations to argue that sub-gridscale motions would often be likely to significantly alter the estimates and resulting parameterizations of GCM-scale surface fluxes in the region.
Date: September 1, 1992
Creator: Shaw, W.J.; Doran, J.C. & Hubbe, J.M.
Partner: UNT Libraries Government Documents Department

Boundary layer structure over areas of heterogeneous heat fluxes

Description: In general circulation models (GCMs), some properties of a grid element are necessarily considered homogeneous. That is, for each grid volume there is associated a particular combination of boundary layer depth, vertical profiles of wind and temperature, surface fluxes of sensible and latent heat, etc. In reality, all of these quantities may exhibit significant spatial variations within the grid area, and the larger the area the greater the likely variations. In balancing the benefits of higher resolution against increased computational time and expense, it is useful to consider what the consequences of such subgrid-scale variability may be. Moveover, in interpreting the results of a simulation, one must be able to define an appropriate average value over a grid. There are two aspects of this latter problem: (1) in observations, how does one take a set of discrete or volume-averaged measurements and relate these to properties of the entire domain, and (2) in computations, how can subgrid-scale features be accounted for in the model parameterizations? To address these and related issues, two field campaigns were carried out near Boardman, Oregon, in June 1991 and 1992. These campaigns were designed to measure the surface fluxes of latent and sensible heat over adjacent areas with strongly contrasting surface types and to measure the response of the boundary layer to those fluxes. This paper discuses some initial findings from those campaigns.
Date: April 1, 1993
Creator: Doran, J. C.; Barnes, F. J.; Coulter, R. L. & Crawford, T. L.
Partner: UNT Libraries Government Documents Department

A field study of the effects of inhomogeneities of surface sensible and latent heat fluxes

Description: In recent years, the problem of characterizing turbulent fluxes of heat, momentum, and moisture over inhomogeneous surfaces has received increasing attention. This issue is relevant to the performance of general circulation models (GCMs), in which a single grid element can encompass a variety of surface and topographical features. Although considerable progress has been made in describing the energy balance at a surface partially covered by vegetation, less is known about how to treat adjacent regions of sharply contrasting surface characteristics. One difficulty is the scarcity of suitable data sets with which to study the problem, particularly on scales of tens to hundreds of kilometers.
Date: January 1, 1992
Creator: Doran, J. C.; Barnes, F. J.; Coulter, R. L. & Crawford, T. L.
Partner: UNT Libraries Government Documents Department

Boundary layer structure over areas of heterogeneous heat fluxes

Description: In general circulation models (GCMs), some properties of a grid element are necessarily considered homogeneous. That is, for each grid volume there is associated a particular combination of boundary layer depth, vertical profiles of wind and temperature, surface fluxes of sensible and latent heat, etc. In reality, all of these quantities may exhibit significant spatial variations the grid area, and the larger the area the greater the likely variations. In balancing the benefits of higher resolution against increased computational time and expense, it is useful to consider what the consequences of such subgrid-scale variability may be. Moreover, in interpreting the results of a simulation, one must be able to define an appropriate average value over a grid. There are two aspects of this latter problem: (1) in observations, how does one take a set of discrete or volume-averaged measurements and relate these to properties of the entire domain, and (2) in computations, how can subgrid-scale features be accounted for in the model parameterizations? To address these and related issues, two field campaigns were carried out near Boardman, Oregon, in June 1991 and 1992. These campaigns were designed to measure the surface fluxes of latent and sensible heat over adjacent areas with strongly contrasting surface types and to measure the response of the boundary layer to those fluxes. This paper discusses some initial findings from those campaigns.
Date: January 1, 1993
Creator: Doran, J. C.; Barnes, F. J.; Coulter, R. L. & Crawford, T. L.
Partner: UNT Libraries Government Documents Department

VERTICAL MIXING AND CHEMISTRY OVER AN ARID URBAN SITE: FIRST RESULTS FROM AIRCRAFT OBSERVATIONS MADE DURING THE PHOENIX SUNRISE CAMPAIGN.

Description: The role of boundary layer mixing is increasingly recognized as an important factor in determining the concentrations of ozone and other trace gases near the surface. While the concentrations at the surface can vary widely due to horizontal transport of chemical plumes, the boundary layer is also characterized by turbulence that follows a diurnal cycle in height and intensity. Surface oxidant concentrations can therefore undergo significant changes even in the absence of photochemistry. A central goal of the Phoenix 2001 Field Campaign was to study vertical mixing with the onset of convection and to quantify the effect of this mixing on chemistry within an urban boundary layer. As part of this study, a series of low altitude aircraft sampling flights were made over the Greater Phoenix area between June 16-30, 2001. The resulting observations, in conjunction with a series of surface measurements and meteorological observations, are being used to study the vertical transport and reactivity of ozone and ozone-precursors shortly after sunrise. Additional details of this campaign are given in Doran, et al. (2002). It was anticipated that turbulence over Phoenix at night would be suppressed as a result of cooling of the boundary layer over the city. By sampling shortly after sunrise, we hoped to collect measurements above the residual nocturnal stable layer and to continue sampling through the developmental period of a convectively active boundary layer. We report here on the first analysis of these observations, made from a Gulstream-1 (G-1) aircraft operated by the U.S. Department of Energy.
Date: January 13, 2002
Creator: BERKOWITZ,C.M.; SPRINGSTON,S.R.; DORAN,J.C. & FAST,J.D.
Partner: UNT Libraries Government Documents Department

Applications of Lagrangian Dispersion Modeling to the Analysis of Changes in the Specific Absorption of Elemental Carbon

Description: We use a Lagrangian dispersion model driven by a mesoscale model with four-dimensional data assimilation to simulate the dispersion of elemental carbon (EC) over a region encompassing Mexico City and its surroundings, the study domain for the 2006 MAX-MEX experiment, which was a component of the MILAGRO campaign. The results are used to identify periods when biomass burning was likely to have had a significant impact on the concentrations of elemental carbon at two sites, T1 and T2, downwind of the city, and when emissions from the Mexico City Metropolitan Area (MCMA) were likely to have been more important. They are also used to estimate the median ages of EC affecting the specific absorption of light, aABS, at 870 nm as well as to identify periods when the urban plume from the MCMA was likely to have been advected over T1 and T2. Values of aABS at T1, the nearer of the two sites to Mexico City, were smaller at night and increased rapidly after mid-morning, peaking in the mid-afternoon. The behavior is attributed to the coating of aerosols with substances such as sulfate or organic carbon during daylight hours, but such coating appears to be limited or absent at night. Evidence for this is provided by scanning electron microscope images of aerosols collected at three sampling sites. During daylight hours the values of aABS did not increase with aerosol age for median ages in the range of 1-4 hours. There is some evidence for absorption increasing as aerosols were advected from T1 to T2 but the statistical significance of that result is not strong.
Date: March 7, 2008
Creator: Doran, J. C.; Fast, Jerome D.; Barnard, James C.; Laskin, Alexander; Desyaterik, Yury; Gilles, Marry K. et al.
Partner: UNT Libraries Government Documents Department

Heterogeneous surface fluxes and their effects on the SGP CART site

Description: The treatment of subgrid-scale variations of surface properties and the resultant spatial variations of sensible and latent heat fluxes has received increasing attention in recent years. Mesoscale numerical simulations of highly idealized conditions, in which strong flux contrasts exist between adjacent surfaces, have shown that under some circumstances the secondary circulations induced by land-use differences can significantly affect the properties of the planetary boundary layer (PBL) and the region of the atmosphere above the PBL. At the Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) site, the fluxes from different land-surface types are not expected to differ as dramatically as those found in idealized simulations. Although the corresponding effects on the atmosphere should thus be less dramatic, they are still potentially important. From an ARM perspective, in tests of single column models (SCMs) it would be useful to understand the effects of the lower boundary conditions on model performance. We describe here our initial efforts to characterize the variable surface fluxes over the CART site and to assess their effects on the PBL that are important for the performance of SCMs.
Date: March 1, 1995
Creator: Doran, J.C.; Hu, Q.; Hubbe, J.M.; Liljegren, J.C.; Shaw, W.J.; Zhong, S. et al.
Partner: UNT Libraries Government Documents Department

Evaluation of empirical atmospheric diffusion data

Description: A study has been made of atmospheric diffusion over level, homogeneous terrain of contaminants released from non-buoyant point sources up to 100 m in height. Current theories of diffusion are compared to empirical diffusion data, and specific dispersion estimation techniques are recommended which can be implemented with the on-site meteorological instrumentation required by the Nuclear Regulatory Commission. A comparison of both the recommended diffusion model and the NRC diffusion model with the empirical data demonstrates that the predictions of the recommended model have both smaller scatter and less bias, particularly for ground-level sources.
Date: October 1, 1979
Creator: Horst, T.W.; Doran, J.C. & Nickola, P.W.
Partner: UNT Libraries Government Documents Department

Evolution of the lower planetary boundary layer over strongly contrasting surfaces

Description: In a multilaboratory field study held near Boardman in northeastern Oregon in June 1991, various properties of the surface and lower atmospheric boundary layer over heavily irrigated cropland and adjacent desert steppe were investigated in the initial campaign of the Atmospheric Radiation Measurement (ARM) program. The locale was selected because its disparate characteristics over various spatial scales stress the ability of general circulation models (GCMS) to describe lower boundary conditions, particularly across the discontinuity between desert (in which turbulent flux of heat must be primarily as sensible heat) and large irrigated tracts (in which turbulent flux of latent heat should be the larger term). This campaign of ARM seeks to increase knowledge in three critical areas: (1) determination of the relationships between surface heat fluxes measured over multiple scales and the controlling surface parameters within each scale, (2) integration of local and nearly local heat flux estimates to produce estimates appropriate for GCM grid cells of 100-200 km horizontal dimension, and (3) characterization of the growth and development of the atmospheric boundary layer near transitions between surfaces with strongly contrasting moisture availabilities.
Date: December 31, 1992
Creator: Coulter, R. L.; Gao, W.; Martin, T. J.; Shannon, J. D.; Doran, J. C.; Hubbe, J. M. et al.
Partner: UNT Libraries Government Documents Department