Showing papers on "Wind shear published in 1978"

Incoherent scatter radar observations of irregular structure in mid‐latitude sporadic E layers

Abstract: The basic experiments used phase-coded pulses to record electron density profiles with a resolution of 600 m in range and 300 m in horizontal extent, while scanning in azimuth. Data from incoherent scatter radar were compared with simultaneous ionosonde observations. Observations of sporadic E layers by incoherent scatter radar were discussed in terms of the effects of the neutral wind system acting on metallic ions. Several features were noted in the data, which support the wind shear mechanism of layer formation. The sporadic E layers often contained a pronounced small-scale structure, especially at times when partially transparent echoes were observed by the ionosonde. Under specific conditions, the ions in a meteor trail can be converged by a shear in the neutral wind into a relatively small irregularity at the center of a sporadic E layer.

Further Evidence of the Mesoscale and Turbulent Structure of Upper Level Jet Stream–Frontal Zone Systems

Abstract: Recent aircraft observations of the mesoscale and turbulent structure of upper level frontal zone-jet stream systems provide further evidence of stratosperic mesoscale cyclonic wind shear and associated anomalously high values of potential vorticity in the layer of maximum wind. Measurements of turbulent heat flux in regions of clear air turbulence above and below the layer of maximum wind (LMW) document the first-order importance of turbulent-scale processes in the generation and dissipation of potential vorticity. Ozone concentration measurements illustrate the intrusion of stratospheric air into the troposphere and give evidence of the effect of turbulent mixing processes in the LMW. It is proposed that the nonconservative property o@ potential vorticity permits air parcels to enter the stratosphere by direct transport across the potential vorticity discontinuity in the LMW, in agreement with earlier isentropic trajectory calculations.

The effect of internal waves on surface wind waves 1. Experimental measurements

Abstract: Internal waves were generated by a ship using the ‘dead water’ effect in areas where the water contains a strong near-surface density gradient. The effects of these internal waves on wind waves were examined. The principal measurements were slope statistics of the wind waves and horizontal currents in the internal waves. The effects on the wind waves were always observable from an aircraft; however, in measurements made only along the ship's track the effects of the internal waves were not always readily distinguishable from other factors that influence the wind wave field. By using statistical techniques, relationships have been established between the wind waves, the internal waves, and the wind velocity. The principal finding is that the wind wave field is relatively more sensitive to internal wave currents at low wind speeds than at high wind speeds. Numerical values are given.

A Three-Dimensional Numerical Model of an Isolated Thunderstorm: Part I. Comparative Experiments for Variable Ambient Wind Shear

Abstract: The mature stage of an isolated convective storm in sheared surroundings is studied by means of an anelastic three-dimensional numerical model. Liquid precipitation and turbulence are included in parameterized form. Three comparative experiments are run with different vertical profiles of ambient wind: no ambient wind, uni-directional shear, and multi-directional shear dominated by strong low-level veering, the first shear profile being the west-east projection of the second. The cases are compared in regard to airflow, pressure, potential temperature and liquid water. The results were as follows: Both sheared storms exhibit a quasi-erect high-speed updraft, a deep cyclonic-anticylonic vortex couplet aloft, middle-level barrier flow around the updraft, and gradual splitting into cyclonic and anti-cyclonic cells moving to the right and left of the mean winds. The model storms show a slightly weaker growing stage with shear than without, but the mature stage is stronger and more persistent. Without...

Temporal and Spatial Scales of the Wind Field over the North Pacific and North Atlantic

Abstract: Quasi-geostrophic wind fields over the northern parts of the Pacific and Atlantic Oceans are calculated from synoptic surface pressure data for the four-year period 1973–76. Maps of mean and rms wind stress and of mean wind stress curl are given. Spectral and cross-spectral analysis reveals the dominant space and time scales of atmospheric disturbances. At periods shorter than 10 days, eastward traveling cyclones dominate the atmospheric variability. At longer time scales the atmospheric spectra are white in frequency and symmetric with respect to wavenumber, and there is no preferred direction of propagation. Differences between the spectra of pressure, wind and wind stress are discussed. To estimate the amount of fluctuations at high wavenumbers which are not present in smoothed synoptic maps, direct wind observations from two weather stations in the North Atlantic are analyzed and compared to synoptic data. It is found that the smoothing is severe for fluctuations with a period shorter than 10...

Engineering handbook on the atmospheric environmental guidelines for use in wind turbine generator development

Abstract: The guidelines are given in the form of design criteria relative to wind speed, wind shear, turbulence, wind direction, ice and snow loading, and other climatological parameters which include rain, hail, thermal effects, abrasive and corrosive effects, and humidity. This report is a presentation of design criteria in an engineering format which can be directly input to wind turbine generator design computations. Guidelines are also provided for developing specialized wind turbine generators or for designing wind turbine generators which are to be used in a special region of the United States.

Algorithm for inferring wind stress from Seasat-A

Abstract: On the SeaSat-A satellite, a microwave scatterometer will be used to infer the wind vector over the world's oceans. This paper describes an algorithm to convert the scatterometer's normalized radar cross-section measurements to sea-surface wind stress and neutral stability wind vector. The algorithm is based on experimental NRCS data from aircraft measurements and a two-scale radar-scattering model. The technique uses Bayes' probabilistic equation to infer the friction velocity vector, from which the wind stress and neutral stability wind vectors are determined. Two examples of inverted radar data are presented: 1) a comparison of aircraftradar-inferred friction velocity vector to that derived from surface wind measurements in the New York Bight and 2) a simulated SeaSat-A measurement inversion in which comparisons are made of the recovered and sample wind fields.

Turbulence detector for non-coherent pulse radar

Abstract: Information about air turbulence and wind shear can be obtained by analyzing the fluctuation of the envelope, at the detector output of a pulse radar, of backscatter from hydrometeors which trace the wind field. Further, under some conditions, radar returns can be identified as being backscatter from weather targets or from the ground or sea. The detector output signal is quantized into one of several class intervals whose boundaries, in mid-range, are in the same ratio. Consecutive radar returns from scatterers at the same nominal range and scan angle are quantized into either the same or different class intervals. The ratio of the number of consecutive quantizations that are different to the number of trials is a measure of the variance of relative velocities at that range and scan angle. This technique permits economical implementation of a plan position display of, for example, the expected severity of turbulence or wind shear at each increment of range and azimuth angle since duplication of circuits is not required.

The growth of duration-limited wind waves

Abstract: Laboratory measurements have been made of the one-dimensional spectra of the duration-limited wind waves which are generated when a wind abruptly begins to blow over a water surface, maintaining a constant speed during the succeeding period of time. The duration dependences of the wave energy E and the spectral peak frequency fm determined from the measured spectra are slightly different from those inferred from the fetch dependences of these quantities. The normalized spectra of the duration-limited wind waves are also slightly different from those of fetch-limited wind waves: the concentration of the normalized spectral energy near the spectral peak frequency is smaller, in many cases, for the duration-limited wind waves than for fetch-limited wind waves. The exponential growth rates β of the duration-limited wind-wave spectra are generally larger than those of fetch-limited wind-wave spectra. Furthermore, both for the duration-limited wind waves and for fetch-limited wind waves the exponential growth rate has a behaviour which is different from the empirical formula of Snyder & Cox (1966). A new empirical formula for the growth rate of the wave spectrum is proposed, from which the empirical formula of Snyder & Cox (1966) can be derived as a special case. Agreement between the new empirical formula and the experimental results is satisfactory for fetch-limited wave spectra, but is confined to the qualitative features for the duration-limited wave spectra.

Meteorological applications of radar

Abstract: Radar has been used by meteorologists for 30 years or so but it is only during the latter half of this period that the full measure of its versatility has come to be recognised. Operationally important techniques have been or are being developed to identify and track severe storms, to provide warning of tornadoes, to measure and forecast rainfall quantitatively, and to measure winds, turbulence and wind shear. At the same time research meteorologists are using specialised radar techniques to investigate many poorly understood aspects of atmospheric behaviour. This review highlights the strengths and limitations of radar as a tool for observing the atmosphere and attempts to provide a balanced view of its many applications in meteorology.

Ground proximity warning system with means for altering warning threshold in accordance with wind shear

Abstract: An aircraft air speed signal is differentiated to provide a signal related to rate of change of air speed. This signal is added to a signal related to aircraft barometric altitude change with the sum signal being compared against aircraft radio altitude to generate warning if the aircraft rate of descent is excessive for the conditions encountered.

Wind shear warning system for aircraft

Abstract: A system to warn an aircraft pilot of a hazardous wind shear condition in which the rate of change of airspeed is compared to the ability of the aircraft to respond thereto Any difference therebetween that exceeds a predetermined threshold is used to activate a suitable alarm or compensation device Additional refinements include correcting the inertial speed inputs for vertical components and autopilot induced throttle changes, and correcting the air speed inputs for short term fluctuations

Wind structure near a city centre

Abstract: This paper describes some characteristics of wind flow over a city area. Extensive measurements were made of the wind structure at a particular site in order to provide a reference for a wind-tunnel simulation of flow over the area. Since full-scale measurements of wind flow over a very rough surface are rare, some results of wider interest are presented here.

Wind shear modeling for aircraft hazard definition

Abstract: Mathematical models of wind profiles were developed for use in fast time and manned flight simulation studies aimed at defining and eliminating these wind shear hazards. A set of wind profiles and associated wind shear characteristics for stable and neutral boundary layers, thunderstorms, and frontal winds potentially encounterable by aircraft in the terminal area are given. Engineering models of wind shear for direct hazard analysis are presented in mathematical formulae, graphs, tables, and computer lookup routines. The wind profile data utilized to establish the models are described as to location, how obtained, time of observation and number of data points up to 500 m. Recommendations, engineering interpretations and guidelines for use of the data are given and the range of applicability of the wind shear models is described.

On the relationship of radar backscatter to wind speed and fetch

Abstract: The physics of the interaction of electromagnetic waves with the ocean surface has been an active area of research for a number of years. This paper contains the results of satellite and aircraft experiments to investigate the ability of active microwave radars to infer surface wind speeds remotely. Data obtained from the recent National Aeronautics and Space Administration (NASA) Skylab experiment are compared with surface wind speeds measured by low-flying aircraft and ships-of-opportunity and found to give useful estimates of the ocean wind field. Also investigated was the influence of varying wave height on radar measurements of wind speed by measuring the backscattering cross-section for constant wind speed but variable wave conditions. It is found that this effect is of little importance.

Wind Power Limitations Associated with Vortices

Abstract: The total pressure dissipation inside vortices due to viscous shear has been analyzed. The reduced level of the total pressure flux of the flow inside a vortex has an adverse effect on all vortex-ingesting wind machines. The Betz limit of wind turbines ingesting the vortex generated by an airfoil has been computed and is nondimensionalized using the area of the vortex generator. The vacuum-pumping ability of vortices is also limited. The Betz-type limit for wind turbines exhausting into the core of a vortex has been computed for both wingtip and tornado-tower-type vortex generators. The energy required to eliminate a tornado has been computed.