Showing papers on "Wind shear published in 1983"

Normal Monthly Wind Stress Over the World Ocean with Error Estimates

Abstract: Over 35 million surface observations covering the world ocean from 1870–1976 have been processed for the purpose of calculating monthly normals and standard errors of the eastward and northward components of the wind stress and work done by the winds in the lower 10 m of the atmosphere. The fields are intended to serve as boundary conditions for models of the ocean circulation. Wind and air-minus-sea temperatures are calculated in a form suitable for determining stress by any bulk aerodynamics model in which the drag coefficient can be represented by six or less coefficients of a second-degree polynomial in wind speed and stability. The particular case of the wind speed and stability dependent drag coefficient discussed by Bunker is selected for analysis. January and July charts of wind stress, curl of the wind stress, mass transport stream-function, divergence of the Ekman transport and the rate of mechanical energy transfer are illustrated and discussed.

Interaction of the Monsoon and Pacific Trade Wind System at Interannual Time Scales Part I: The Equatorial Zone

Abstract: The time history of the Monsoon System over the Indian Ocean has been developed from ship observations and merged with the Wyrtki-Meyers Pacific Trade Wind field. The interaction of these two massive wind systems has been studied by a rather new empirical orthogonal function (EOF) analysis capable of detecting propagating features in the wind systems. The current study (Part I) was confined to variations within ±10° of the equator. Results show the two wind systems are strongly coupled at interannual time scales. The coupling is effected through cyclostationary pulsations and longitudinal shifts of the huge surface convergence over Indonesia. The interaction may also he thought of as the spatial expansion/contraction of the wind systems. These changes can be viewed as the transition of the Monsoon/Trade Winds between two preferred climate states. One sub-element of this apparent bimodality in the wind fields is the El Nino phenomenon. The zonal component of the combined wind fields seems to insti...

Evaluation of Doppler radar for airport wind shear detection

Abstract: The utility of Doppler radar measurement techniques for detecting low-level wind shear at airports is examined. The Doppler radar data of the Joint Airport Weather Studies (JAWS) for windshear microburst features are analyzed, in order to determine the optimal resolution, sensitivity, and scanning strategy for a standard system. The performance of three separate systems for measuring wind shear at heights of less than 200 meters is compared. The three systems included a dual-Doppler system, a single off-airport Doppler system, and a single on-airport Doppler system. On the basis of the comparison the following recommendations are offered concerning the optimal performance of a Doppler radar system in the airport environment: (1) the system should be able to measure radial velocities over a range of reflectivity of -10-80 dBZ; (2) ground clutter should be reduced; and techniques for identifying and disseminating wind shear information should be automated.

January and July Simulations with a Spectral General Circulation Model

Abstract: We describe the results of January and July simulations carded out with a nine-level spectral model, employing a rhomboidal truncation at wavenumber 15. Sea-surface temperature, sea-ice distribution and solar zenith angle are held constant in each simulation. The model includes interactive clouds and radiative processes after Ramanathan et al. (1983). Selected fields are shown which highlight the model's strengths and weaknesses. The latitude-height distribution of the zonal wind is successfully simulated. The model captures the separation between the wintertime westerly jets in the troposphere and stratosphere and thus simulates the sign reversal in the vertical wind shear across the jet axis in the upper troposphere. In addition to the zonal wind, we show also the zonally averaged temperature, meridional wind and vertical velocity. Regional distributions of sea-level pressure, surface air temperature, precipitation and a number of other fields defined at various pressure levels are compared in ...

Wind Effects on Gas‐Liquid Transfer Coefficients

Abstract: A relationship between the transfer coefficient of sparingly soluble gases and wind velocity is developed in terms of the liquid film and surface renewal concepts. When a wind blows over water, shear is exerted at the interface, which establishes the structure of the boundary layers in both media. The dynamic characteristics of these interfacial regions influence the rate of transfer between air and water. The functions relating the viscous sublayer and roughness height with the wind shear provide the basis for the development of equations which define the transfer coefficient for both smooth and rough surface conditions. The relationships are applied to the exchange of volatile organic chemicals which are characterized by liquid film control.

On Symmetric Stability and Instability of Zonal Mean Flows Near the Equator.

Abstract: Obserations of longitudinally-averaged zonal flows in the atmosphere and ocean tend to display north–south symmetry about the equator, with a characteristic wind maximum or minimum, and therefore little horizontal wind shear locally near the equator. It is shown that this configuration is required for balanced flow on a sphere to be inertially stable. If dissipation can be neglected, any horizontal wind shear at the equator will cause inertial instability to develop. effectively eliminating the horizontal shear. It follows that the potential vorticity (q) must vanish at the equator for the symmetric circulation to be stable; and that it must increase to the north and decrease to the south. Balanced cross-equatorial flow can occur only if there is a north–south gradient in the torque or the diabatic heating at the equator. These conclusions are obtained under the assumption of a balanced zonal flow; i.e., acceleration and dissipation are explicitly neglected in the meridional momentum equation. Th...

Aerodynamic penalties of heavy rain on landing airplanes

Abstract: The aerodynamic penalties due to very heavy rain on a landing aircraft is addressed in this paper. Based on severity and frequency of occurrence, torrential rainfall rates of 100, 500, and 2000 mm/h were investigated. Significant momentum loss was found to occur at moderate and higher torrential rainfall rates. The weight of a water film on transport category aircraft was found to be only a small fraction of landing weight. Roughness of an airfoil in rain is caused by drop cratering and waviness to a thin film on the airfoil and fuselage. Both sources of roughness were found to separately produce drag increases of from 5 to 10% for a 100-mm/h rain increasing to 15 to 25% for a 2000-mm/h rain. In addition, lift decreases of 10% for a 100-mm/h rain to more than 30% for a 2000-mm/h rain were estimated. Exordium I N recent years, wind shears associated with strong thunderstorm downdrafts have been implicated as the cause of several airplane accidents. The Eastern Flight 066 accident at Kennedy Airport1 is a prime example. In the National Transportation Safety Board's reconstruction of the flight recorder data from the accident, extraordinarily large wind shears were estimated. The reconstruction considered no other external factors besides the wind. The performance degradation due to the torrential rain cell experienced by Eastern 066 was not taken into account. We feel it possible that the derived wind shears are too large because the effect of the very heavy downpour was ignored. An extensive literature source revealed only one other investigation2 which considered the effect of torrential rain on airplane performance. That investigation dealt with the case of an airplane encountering torrential rain at moderate

Meridional neutral winds in the thermosphere at arecibo: simultaneous incoherent scatter and airglow observations

Abstract: Simultaneous measurements of ion and neutral wind velocities have been obtained at Arecibo, Puerto Rico, on several nights in both the summer and winter seasons. The diffusion velocity of O+, calculated in an analysis by using the accepted value for the ambipolar diffusion coefficient and the MSIS model atmosphere, is found to be in fairly close agreement with the observations. Incoherent scatter radar data have also been used to derive height profiles of the meridional neutral wind velocity. In the spring and summer months, the meridional wind is strongest near 2100 AST, with a southward velocity ranging from 50–100 m s−1. At about 0100 AST the ‘midnight descent’ of the F layer occurs, in association with a slackening, or sometimes a reversal, of the meridional wind. In general, the meridional wind is fairly constant with altitude. However, prior to midnight in the spring and summer months, contours of constant velocity are often observed to slope downward with increasing time. Some degree of vertical wind shear is often observed between 0200 and 0500 AST as well. In the winter months, meridional wind velocities are lower, and the nocturnal variation of the wind field is less pronounced than it is at other seasons.

The Influence of Coastal Shape on Winter Mesoscale Air-Sea Interaction

Abstract: In the case of cold air outbreaks, the combination of the coastal shape and the sea surface temperature (SST) pattern is shown to have a profound effect in establishing a low level mesoscale atmospheric circulation as a result of differential heating due to both variations in overwater path length and the SST. A convergence (or divergence) line then forms along a line exactly downwind of the major bend in the coastline. This is consistent with the structure of the cloud patterns seen in a high resolution Landsat picture of the cloud streets. The major features are also simulated well with a boundary layer model. The dominant convergence line is marked by notably larger clouds. To its cast the convective roll clouds grow downstream in accord with the deepening of the boundary layer. To its west (i.e., coastal side) near the convergence line where the induced pressure field forces a strong westerly component in the boundary layer, the wind shear across the inversion gives rise to Kelvin-Helmholtz w...

The fine structure of the stratospheric flow revealed by differential sounding

Abstract: Preliminary results concerning the fine vertical structure of the stratospheric flow in the middle stratosphere, above 18 km, are presented. By using a high-resolution anemometer hung below slowly rising and descending balloons, the wind shear vector was measured over vertical distances as small as 50 m. Most of the soundings reveal an organized structure with a vertical wavelength of about 1 km. Shear instabilities are generally related to these structures. These observations, more detailed than those obtainable using radar-balloon methods, suggest that long-period inertio-gravity waves are responsible for much of the variability.

Characteristics of air flow above and within soybean canopies

Abstract: Air flow was observed above and within canopies of a number of kinds of soybeans. The Clark cultivar and two isolines of the Harosoy cultivar were studied in 1979 and 1980, respectively. Wind speed above the canopy was measured with cup anemometers. Heated thermistor anemometers were used to measure air flow within the canopy. Above-canopy air flow was characterized in terms of the zero-plane displacement (d), roughness parameter (z o) and drag coefficient (C d). d and z o were dependent on canopy height but were independent of friction velocity in the range 0.55 to 0.75 m s−1 · C d for the various canopies ranged from 0.027 to 0.035. Greater C d values were measured over an erectophile canopy than over a planophile canopy. C d was not measurably affected by differences in leaf pubescence. Within-canopy wind profiles were measured at two locations: within and between rows. The wind profile was characterized by a region of great wind shear in the upper canopy and by a region of relatively weak wind shear in the middle canopy. Considerable spatial variability in wind speed was evident, however. This result has significant implications for canopy flow modeling efforts aimed at evaluating transport in the canopy. In the lower canopy, wind speed within a row increased with depth whereas wind speed between two rows decreased with depth. The wind speeds at the two locations tended to converge to a common value at a height near 0.10 m. The attenuation of within-canopy air flow was stronger in canopies with greater foliage density. Canopy flow attenuation seemed to decrease with increasing wind speed, suggesting that high winds distorted the shape of the canopy in such a manner that the penetration of wind into the canopy increased.

Surface Meteorological Observations in Severe Thunderstorms. Part II: Field Experiments with TOTO

Abstract: The TOTO (Totable Tornado Observatory) device was field tested in the Southern Plains by a severe-storm intercept team from the University of Oklahoma from late May through early June 1981 The results from two intercept missions and a gust-front intercomparison at the National Severe Storms laboratory are discussed Measurements are presented of wind speed, wind direction, pressure and temperature made underneath a rotating wall cloud and within 15 km of two tornadoes A damage survey and a Doppler-radar observed mesocyclone-signature track were used in conjunction with the TOTO data to obtain an estimate of the maximum wind speed inside one of the tornadoes

Sea surface winds from sun glitter observations

Abstract: Solar light reflected by the surface of the sea depends strongly on the sea state which is driven by the wind. The relationship between the reflected light and wind speed is described by the well-known model of Cox and Munk. Using their model, a method is derived for the retrieval of the synoptic field of wind magnitude from measurements of the glitter pattern from space. This method is applied to data obtained by the TIROS-N satellite series. Comparison of the wind estimated in this way and the wind derived from isobaric charts shows very close agreement. The method is simple and has application over broad geographical areas.

Pitch control system for large-scale wind turbines

Abstract: The purpose of this analysis is to study the design of a pitching blade segment control system for the NASA-DOE MOD 0 wind turbine to alleviate some of the problems associated with shear, tower shadow, and gravity phenomena, such as shortened lifetime and noise generation. The classical linear quadratic Gaussian optimal regulator approach is used in the control formulation. A quasisteady aerodynamic analysis incorporating wind shear and tower shadow is utilized. An equivalent hinge model describes the turbine structural dynamics. The study shows that the proposed control system can provide significant vibration and noise reduction as well as a cleaner power signal, better gust response, and increased annual energy output.

Wave-CISK in Mass Flux Form

Abstract: A reformulation of wave-CISK shows that gravity waves generated by the divergence of cumulus mass fluxes am responsible for the forcing of further convection. When downdrafts are included, a new, non-propagating instability arises. This mode has a growth rate much larger than the usual, propagating wave-CISK mode, but requires the downdraft mass flux to exceed a certain critical value. The nonpropagating mode apparently corresponds to air-mass thunderstorms, whereas the propagating mode suggests long-lived convection. The two modes respond very differently to wind shear.

The sensitivity of upper ocean structure to time varying wind direction

Abstract: Observations and models show that sudden changes in the magnitude of the wind stress which occur within a time interval of one-half inertial period are most effective in increasing surface current speeds and mixing the upper layers of the ocean. The purpose of the present study is to quantify the effects of concurrent time dependent wind direction. The Mellor-Yamada level 2 1/2 turbulence closure model is used. A series of model runs was executed in order to determine the relative sensitivity of mixed layer depth and sea surface temperature to wind speed as compared with the rate of change of wind direction. The results indicate that the accuracy and time resolution of wind direction should be given special consideration in the design and interpretation of field experiments which will be used for testing prognostic mixed layer models.

Convective Heat Losses From Flat-Plate Solar Collectors in Turbulent Winds

Abstract: This paper presents results for convective heat transfer coefficients on the surface of flat-plate solar collectors mounted on a single-family residential building and exposed to the wind. The results were obtained by testing a 1:32 scale model in highly turbulent nonuniform flows which simulated the natural wind. For full-scale conditions, the heat transfer coefficients are two to three times lower than those given by a commonly used correlation. The coefficients show some sensitivity to wind direction but are insensitive to the characteristics of the wind and to architectural details of the building.

Mesospheric radar echoes at Poker Flat, Alaska: Evidence for seasonally dependent generation mechanisms

Abstract: The long-term character of VHF mesospheric echoes obtained by using the Poker Flat MST radar in Alaska show the following characteristics: (1) The winter time echoes are relatively weak and are only present in the height range 55–80 km, while (2) the summertime echoes are much stronger, with the maximum echo intensity centered at 86 km. The evidence currently available indicates that the winter time echoes arise, from the nonlinear breakup of tropospherically generated gravity waves. The stronger summertime echoes, on the other hand, appear to arise in situ as a result of the combined effects of the steep summertime vertical temperature gradient that exists at these latitudes and the horizontal wind shears.

Wind measurements from an array of oceanographic moorings and from F/S Meteor during JASIN 1978

Abstract: During the Joint Air-Sea Interaction (JASIN) experiment conducted in the northern Rockall Trough in the summer of 1978, oceanographic moorings with surface buoys carrying wind recorders were deployed in an array designed to investigate the variability of the near-surface wind field at scales of from 2 to 200 km. The wind records together with observations taken on board the research vessels participating in JASIN have provided ground truth measurements for the sea surface wind velocity sensors on the Seasat satellite. During most of the experiment the wind field was characterized by spatial scales large in comparison with the separations between the buoys. On several occasions, spatial differences associated with cold fronts were identified, and it was possible to track the passage of the front through the array. However, quantitative analysis of the variability of the wind field was complicated both by a lack of data due to mechanical failures of some instruments and by significant differences in the performance of the diverse types of wind recorders. Reevaluation of the instruments used in JASIN and recent comparison of some of these instruments with more conventional sets of wind sensors confirm the possibility that there is significant error in the JASIN wind measurements made from the buoys. In particular, the vector-averaging wind recorder on W2, which was one of the few instruments to recover a full length record and which was chosen during a Seasat-JASIN workshop as the JASIN standard, had performance characteristics that were among the most difficult to explain.

Wind Speed‐Damage Correlation in Hurricane Frederic

Abstract: Hurricane Frederic of 1979 caused wind damage to buildings, power lines, and trees in the coastal areas of Alabama, Florida, and Mississippi. Wind speeds were recorded in Hurricane Frederic at sufficient number of stations to establish maximum ground level wind speed regimes in affected communities. The established wind speeds are fastest‐mile wind speeds at 10 m height in flat, open terrain. Thus, established values are similar in character to those employed in building codes. Evaluations of the performance of buildings reveal that fully engineered buildings performed well, even when wind speeds were sligritly above code specified values. One common damaging mode was breakage of glass windows by windborne debris. There was significant structural damage to pre‐engineered and marginally engineered buildings, including some frame collapses in wind regimes corresponding to or slightly in excess of code specified values. Damage to these types of buildings was attributed to “weak links” and was influenced by l...

Flight in low-level wind shear

Abstract: Results of studies of wind shear hazard to aircraft operation are summarized. Existing wind shear profiles currently used in computer and flight simulator studies are reviewed. The governing equations of motion for an aircraft are derived incorporating the variable wind effects. Quantitative discussions of the effects of wind shear on aircraft performance are presented. These are followed by a review of mathematical solutions to both the linear and nonlinear forms of the governing equations. Solutions with and without control laws are presented. The application of detailed analysis to develop warning and detection systems based on Doppler radar measuring wind speed along the flight path is given. A number of flight path deterioration parameters are defined and evaluated. Comparison of computer-predicted flight paths with those measured in a manned flight simulator is made. Some proposed airborne and ground-based wind shear hazard warning and detection systems are reviewed. The advantages and disadvantages of both types of systems are discussed.

Worldwide Experience of Wind Shear during 1981-1982,

Abstract: : Large changes of wind and downdraughts (Wind Shears) have caused several major accidents to airliners. The Royal Aircraft Establishment (RAE), with support from the United Kingdom Civil Aviation Authority and British Airways (BA), have analysed wind shear data from over 9000 landings by 26 BA B747 aircraft at 71 airports around the world during 1981 and 1982. The data are analysed using Discrete Gust methods developed at the RAE. Time histories of wind velocities and aircraft reactions are presented for 9 of the more interesting events identified. These were selected from 86 examples of large wind shears where the three components of wind velocity have been calculated. An example of a severe downburst in the vicinity of a thunderstorm is also presented. This was measured by the RAE HS125 research aircraft during the Joint Airport Weather Studies (JAWS) Programme near Denver, Colorado, USA in July 1982. Statistics on the probabilities of encountering wind shears with particular patterns of headwind speed changes have been calculated from the 9000 landings. Effects at different airports, height bands, shear lengths, and patterns have been compared. Suggestions are made for Design Cases of shear that could be used for testing autopilots and wind shear measuring systems. Some possible criteria for the severity of single ramp changes in headwind are presented. (Author)

Wind tunnel generation of horizontal roll vortices over a differentially heated surface

Abstract: Wildland crown fires represent an extreme type of forest fire that advances from top to top of trees or shrubs. Some such fires generate energy comparable to several nuclear explosions. They occur most frequently in coniferous forests found in the United States and Canada, and in broad-leafed eucalyptus forests of Australia. Here we report visualization of wind tunnel experiments in which airflow along the perimeter of a simulated forest fire produced horizontal vortex pairs with axes in the downstream direction. These vortex pairs formed above a differentially heated surface simulating the thermal energy flux from a crown fire. The thermal energy was produced by an electrically heated surface ribbon at a temperature of ∼250°C and also, in a separate experiment, by an electrically heated embedded wire coil at a temperature of ∼825°C. Wind velocities ranged from 0.2 to 3.6 m s−1. Similar vortex action may cause the unburned tree-crown strips that are observed when crown fires, driven by a significant wind, burn over flat terrane.

Response to Wind Action of 265‐M Mount Isa Stack

Abstract: Measurements were made of the response to wind action of the 265‐m high, reinforced concrete stack at Mount Isa Mines in Queensland, Australia. Data were reduced from accelerometer, strain gage and pressure transducer records from four wind storms. Particular attention was paid to determining reference freestream wind speeds at stack height and wind structure, which involved using records from a number of anemometer sites and for which position errors were determined from topographical model studies in a boundary layer wind tunnel. In this paper, the full scale data are reduced and presented such that they can readily be used to compare with results from physical and mathematical model studies of stack response to wind action. Mean, standard deviation and peak tip displacements, and base overturning moment coefficients are given, along with estimates of structural damping, peak factors and dominant wake frequencies, at Reynolds numbers up to 2×107.