Wind Speed Ratio Research Articles

The relationship of hurricane reconnaissance flight-level wind measurements to winds measured by NOAA's oceanic platforms

A well-known problem in hurricane forecasting and in the administration of hazardous weather warnings and advisories concerns what adjustment to make to flight-level reconnaissance wind observations in order to make them representative of sustained surface winds. To solve this problem, a study was initiated comparing NOAA reconnaissance flight-level winds to 10 m level observations from NOAA's oceanic buoys and platforms. A data base was created that consisted of comparisons made whenever the aircraft observation was: (1) within 10 km radial seperation from the surface platform (in a storm-relative coordinate system), (2) within ±4 h of the surface observation time, (3) within ±2 h of the surface observation time. The data base contains all storms flown by NOAA aircraft in the vicinity of the Atlantic and Gulf of Mexico buoy network over the eleven year period from 1975–1986.Comparisons from these criteria are discussed in terms of the ratio of the buoy-measured wind speed (VB) to the aircraft measured wind speed VA. Results indicate that the 10 m level surface winds over water were within 55–85% of the winds measured by the reconnaissance aircraft. The ratio VB/VA depended strongly on the low-level atmospheric stability as indicated by the buoy air-sea temperature difference.

Winter Offshore/Onshore Wind Differences in Southeastern Hudson Bay, Canada

Acquisition of two 38-day wind data sets collected over a fast-ice shelf and at a nearby coastal weather station (Kuujjuarapik) in Hudson Bay allowed the calculation for the first time of an offshore/onshore wind speed ratio for an ice-covered environment. Mean wind over the ice was 29% higher than at the coast, compared to values of 65% for open ocean locations. This reflects the effect of the higher drag coefficient of the sea ice that more strongly attenuates the wind than does the sea surface. The data set also allowed the evaluation of the change in the wind field by local topography. Thus, a strong orographic effect was found in the SW quadrant, as winds of less than 5 m/s were deflected toward the SE and NW.

An investigation of winds up to 300 hPA over Turkey between 1970 and 1984

AbstractTurkish radiosonde data obtained at the meteorological stations in Istanbul, Ankara, and Izmir have been analysed in order to study the winds between 850 hPa and 300 hPa pressure levels between 1970 and 1984. The monthly mean values of both the zonal (ū) and the meridional (v̄) wind velocity components, their variances, σ2u and σ2v, and the monthly mean values of wind direction, α, were statistically determined. The constancy, Q, of the winds was then computed by taking the ratio of the monthly mean resultant wind speed (V̄t) and the monthly mean scalar wind speed (V̄s). The results were interpreted by taking local wind patterns into consideration.

練習帆船日本丸の帆走性能実験について

The NIPPON MARU, 2570 ton 4-masted bark, was built in 1984 to replace former NIPPON MARU as a sail training ship for the cadets of Institute for Sea Training, Ministry of Transport, Japan. The authors have carried out the experiments to measure her sailing speed, leeway, apparent wind direction and speed and others in trade-wind zone of the North Pacific Ocean. In analyzing these experimental data, we have got ship speed/true wind speed ratio for each trim angle of yards and sail condition. Secondly, we have got aerodynamic coefficients of her sails, by solving the equilibrium equations in steady sailing conditions. The results are as follows. In respect of ship maneuvering, she made a speed of more than 75% of true wind speed in close-hauled under fullsails, when her propellers were revolving freely. Stays'ls were effective when she sailed in the range from close-hauled to beam reach condition. In following wind condition she made a speed of 20% of the true wind speed under fore and aft sails only. In respect of aerodynamic performance, her sails stalled at 25 degrees of the attack angle and had a considerably larger lift and drag forces than those by wind tunnel test. Her thrust force coefficient was maximum at close-reaching because of no interference of the aft sails to the fore sails, and thrust force mainly depended on her sail area.

Topographic Effects on Destruction of Stable Layer during Nighttime

To research regional difference of frost damage, meteorological observations were made at Hayakita, located in the south-east of the Ishikari-Yuhutsu plain in Hokkaido. Hayakita has crops that are the most easily damaged by frost in the plain. In particular paddy rice plants are damaged by the first frost when their growth is retarded by a cool summer. The first frost in Hayakita occurs 1 week earlier than in other parts of the plain. To research this problem, Chitose that has different topography from Hayakita, was selected as a control area and some meteorological factors such as air temperature, wind speed, solar radiation, net radiation and downward radiation were compared between Hayakita and Chitose. These areas are at the same altitude and share similar surface features. Although Hayakita is surrounded by hills, Chitose is in the center of the plain and is located 12 kilometers away from Hayakita.In this paper, the daily minimum air temperatures and 4-hour mean values of the meteorological factors in the springs and falls of 1983 and 1984 were compared between Hayakita and Chitose. Also the variations of these factors on clear nights were compared.Daily minimum air temperatures in both seasons were not significantly different between Hayakita and Chitose. This means that the advection and accumulation of air mass cooled on surrounding slopes are not significant as causes of the frost damage in Hayakita.The 4-hour mean value of wind speed at Chitose was always greater than that at Hayakita. However, there were no significant differences for the other factors, such as solar radiation, net radiation and downward radiation between Hayakita and Chitose. The air temperature in Hayakita was often lower than that in Chitose, especially in the lower range of temperatures. This tendency was more remarkable in fall than in spring. Sometimes the temperature difference between the two regions reached approximately 5K in fall, accompanied with a large difference of wind speed.This large difference of air temperature tended to be observed from 20:00 to 4:00 of clear nights. It was caused by temperatures in Chitose often being rapidly increased by raising wind speed during that time, but both temperature and wind speed in Hayakita remained low and unchanged. When comparing temperature profiles to 80 meters above ground level of both regions, it was noted that the stable layer formed by radiative cooling was destroyed from upper portion to near ground surface at Chitose, while, on the other hand, only the upper portion of the layer was destroyed at Hayakita. However, both stable layers remained during the nights when no temperature difference occurred between the regions. Therefore, the occurrence of temperature differences between the regions is due to the difference in the destruction ratio of the stable layer.The phenomena mentioned above, often appeared in the center of the plain when the upper wind (geostrophic wind) speed and/or direction changed. The upper wind data were obtained from radiosonde data at the 900mb isobaric surface above Sapporo. The changes of wind were classified by following two patterns: i) upper wind speed very small at first, becoming stronger later, and ii) upper wind direction changing from a direction in which WSR (Wind Speed Ratio: the ratio of surface wind speed to upper wind speed at a direction) is small to other one in which WSR is greater. Greater WSR means greater wind speed at ground level for a given upper wind speed; WSR is influenced by surrounding geographic features. Therefore, the WSR values at the center of the plain, lying between the high mountains to the east and west, were large for the north-south direction and small for the east-west direction. On the other hand, WSR values were relatively small for all directions in Hayakita. Thus wind speed in Hayakita was always smaller than that in the center of the plain.It can thus be recognized that low temperatures conti

Directional spectra of wind-generated ocean waves

From observations of wind and of water surface elevation at 14 wave staffs in an array in Lake Ontario and in a large laboratory tank, the directional spectrum of wind-generated waves on deep water is determined by using a modification of Barber’s (1963) method. Systematic investigations reveal the following: ( a ) the frequency spectrum in the rear face is inversely proportional to the fourth power of the frequency w, with the equilibrium range parameter and the peak enhancement factor clearly dependent on the ratio of wind speed to peak wave speed; ( b ) the angular spreading 0 of the wave energy is of the form sech 2 (fid), where /? is a function of frequency relative to the peak; ( c ) depending on the gradient of the fetch, the direction of the waves at the spectral peak may differ from the mean wind direction by up to 50°, but this observed difference is predictable by a similarity analysis; ( d ) under conditions of strong wind forcing, significant effects on the phase velocity caused by amplitude dispersion and the presence of bound harmonics are clearly observed and are in accordance with the Stokes theory, whereas ( e ) the waves under natural wind conditions show amplitude dispersion, but bound harmonics are too weak to be detected among the background of free waves.

Measurements of the wind-wave energy flux in an opposing wind

A wind-wave flume which allows mechanically generated water waves to propagate in opposition to a boundary-layer air flow has been used to measure the air-flow structure in an opposing wind—wave situation. Measurements of the wave-induced pressure closely follow the predictions of potential flow theory, with the pressure in antiphase with the water surface. Hence, in contrast to the following wind situation, there is no appreciable air—water energy flux due to normal stresses. The vertical and horizontal wave-induced velocities deviate slightly in magnitude from the potential flow result while still following it qualitatively. Based on these velocity measurements it is determined that the Reynolds stress—ρa ūū is the dominant term in causing the decay of waves in opposing winds. The predicted rate of decay has a squared dependence on the wave slope and the ratio of wind speed to wave phase speed. © 1985, Cambridge University Press. All rights reserved.

An Analysis of the AVE–SESAME I Period Using Statistical Structure and Correlation Functions

Structure and correlation functions are used to describe atmospheric variability during the 10-11 April day of AVE-SESAME 1979 that coincided with the Red River Valley tornado outbreak. The special mesoscale rawinsonde data are employed in calculations involving temperature, geopotential height, horizontal wind speed and mixing ratio. Functional analyses are performed in both the lower and upper troposphere for the composite 24 h experiment period and at individual 3 h observation times. Results show that mesoscale features are prominent during the composite period. Fields of mixing ratio and horizontal wind speed exhibit the greatest amounts of small-scale variance, whereas temperature and geopotential height contain the least. Results for the nine individual times show that small-scale variance is greatest during the convective outbreak. The functions also are used to estimate random errors in the rawinsonde data. Finally, sensitivity analyses are presented to quantify confidence limits of the structure functions.

Corotating interaction regions in stellar winds

In a stellar wind, a corotating interaction region (CIR) is formed when a rotating star emits wind in a non-spherically symmetric manner. CIRs have been studied in detail in the solar wind: here, their role in stellar winds is considered. The radial distance at which CIRs form (in terms of the stellar radius) is proportional to the ratio of wind speed to the rotational speed at the stellar surface: in the sun, this ratio is approximately 200, but it may be much smaller than that in other stars. The properties of CIRs appear to be able to account for certain features of 'hybrid stars' (i.e., cool giants with cool winds plus 'warm' lines in their UV spectra), for X-ray emitting structures in hot star winds, and for the appearance of extended chromospheres in cool supergiants.

Air‐ice drag coefficients for first‐year sea ice derived from aircraft measurements

Turbulent flux measurements were made at four levels (42, 90, 195, and 340 m) by the NOAA P‐3 aircraft over first‐year sea ice in the northern Bering Sea during February 1982. Three profiles of momentum flux and mean wind were used to calculate an air‐ice drag coefficient CD of 3.0 ± .6 × 10−3 referenced to a 10‐m anemometer height. The boundary layer was slightly unstable (zi/L = −1.2, where zi, was the inversion height of 660 m and L the Monin‐Obukhov length). The mean wind speed at the 42‐m height was 17 m/s, and the air temperature was −20°C. From turbulent heat flux measurements the value of the bulk heat transfer coefficient CH was 0.73 ± 1.6 × 10−3, giving a CH/CD of 0.24. The Bowen ratio was greater than 2.8. Comparison of the present turbulent flux and variance profiles with those collected over the ocean shows agreement, which increases confidence in the calculations. The geostrophic drag coefficient |u*|/|G|, where u* is the friction velocity and G is the geostrophic wind, was 0.047. The turning angle of the surface wind (measured by an anemometer at a height of 3 m on the ice) was 32°, and the ratio of surface wind speed to the geostrophic wind speed was 0.76.

Requirements for modeling of a snowdrift

In an experiment of a model snowdrift formed behind each of two model snow fences, which are the same in shape but different in size, the independence of the wind speed ratio between them from their length ratio was observed. This phenomenon can be explained not by the Froude number, but by the effect of wakes behind an obstruction and movement characteristics of snow particles. The wind speed ratio and the duration of a storm in which the model snowdrifts of glass beads and activated clay particles become similar to each other, were examined. It follows from the result that the friction speed ratio is equal to the ratio of the threshold friction speed of both model snow particles, and the ratio of storm duration can be calculated by comparing the volume of both model snowdrifts. This result suggests strongly that the same relationships hold between the model and the prototype snowdrift.

Day to night wind speed ratios over India

Day to night wind speed ratios over India

Terrain-induced downwash effects on ground level SO 2 concentrations

A field study was conducted at the Tennessee Valley Authority's (TVA) Widows Creek Steam Plant from March to 1 May 1979 to investigate the effects of terrain-induced downwash. The Widows Creek Plant is located in a valley formed by Sand Mountain to the southeast and the Cumberland Plateau to the northwest. With southeasterly winds, a downward component of velocity is induced by the terrain as the air moves from Sand Mountain across the valley. Because of the proximity of the plant to Sand Mountain, the plumes are caught in this terrain-induced downwash, which then causes a significant increase in the ground level SO 2 concentrations. An SO 2-monitoring network was established in the downwash region and the measured SO 2 concentrations were correlated with the meteorological parameters and plant operating conditions. The maximum SO 2 concentrations were measured within 1.3 km of the source at locations approximately perpendicular to the Sand Mountain ridge line. The ground level concentration per unit emission rate increased with increasing wind speed and the ratio of wind speed to stack exit velocity. Neither the magnitude nor the trends predicted by the CRSTER model compared well with measured data unless the plume was assumed to be suppressed by the terrain-induced downwash. The CRSTER model predicted a maximum concentration for class A stability and negligible values for class D to G. Ground level concentrations were not measured during the few periods of class A stability that occurred. The highest concentrations were measured for stability class C and D conditions.

A revaluation of the Kansas mast influence on measurements of stress and cup anemometer overspeeding

For the 1968 Kansas atmospheric surface-layer experiment, a supplementary analysis is made of the evaluation procedure. Available data on the ratio of wind speeds measured on separate booms show a variation with wind direction which is too large for an open mast. Actually the Kansas mast appears to have carried a bulky array of apparatus at the sonic anemometer levels. It is shown that the air flow interference caused by this obstacle can be satisfactorily estimated by way of potential flow calculations. From these it follows that the sonic anemometer measurements probably have undervalued the free-flow eddy stress by 20% to 30%, which implies that the simultaneous drag plate measurements of stress were generally correct. Also the overestimation of the mean wind speed by the Kansas cup anemometer is found to have been 6% rather than 10%. Some Kansas evaluation results are amended accordingly. The von Karman constant is found to be 0.41 rather than 0.35, and the near-adiabatic eddy diffusivity ratio K H /K M becomes 1.0 rather than 1.3. The flux-gradient relations (Businger et al., 1971) after similar revision no longer differ significantly from those obtained elsewhere.

Stability Dependence of the Ratio of Wind Speeds at Two Levels over Agriculture Land

Abstract Hourly averaged winds are computed from a one-year record taken atop five 10 m towers and four 30 m towers distributed over 4000 km2 of typical agricultural land. Vertical temperature differences are available from three of the 30 m towers. The ratio of spatially averaged speeds at the two levels is plotted against a mean bulk Richardson number. The range of stability where measurements are possibly consistent with the presence of established similarity profiles is limited and dependent on wind speed. However, the speed ratios follow smoothly varying functional relations over a wide range of stability for each classification of data by season and wind speed.

A comparison of turbulence classification schemes

Various schemes for classifying the atmospheric turbulence in terms of the Pasquill A-F classes are compared and assessed. This classification is necessary in some aspects of air pollution control strategies that involve the use of dispersion models based on the Gaussian formulation. In particular the ΔT and σ θ methods of the Nuclear Regulatory Commission, the STAR program, Richardson and bulk Richardson numbers, and a parameter defined as the ratio of wind speeds at two levels are compared. The results indicate that in terms of overall distributions, some of the methods compare favorably to the σ θ method which is used as the basis of comparison. However, simultaneous turbulence category determinations by the various methods, on an hourly basis, do not correlate well except for the neutral class. Possible reasons for the discrepancies are discussed. The implications for modeling of concentration estimates are briefly evaluated.

Ventilation of Greenhouses

The primary need for ventilation of greenhouses is to prevent excessive rise of temperature in sunny days, and the other needs are to replenish the carbon dioxide and to lower an excessive level of humidity. In the design stage of a greenhouse equipped with natural ventilation, it is very useful if the natural ventilation rate can be calculated theoretically as a function of (i) greenhouse structures, (ii) arrangements of ventilators or other openings and (iii) wind speed and wind direction.It is possible to estimate the ventilation rate from the pressure differences across openings and the resistances to air flow through openings. Pressure and discharge coefficients of openings for a single-span greenhouse with continuous side and ridge ventilators, and entrance/exit at gable end were determined experimentally. A one-fifteenth model was installed in a boundary layer wind tunnel for the experiments. The wind speed profile in the wind tunnel was adjusted to be the logarithmic profile with the roughness length of 0.067mm, which is a representative value observed often in nature. Based on the measurements of internal pressures and mean air speeds through openings, pressure and discharge coefficients were determined from the equations (10), (14) and (15).The results are presented in Fig. 6, Table 1 and Fig. 7. Some noticeable features are as follows:(1) All pressure coefficients across openings were not equal to those over surfaces at the ventilators closed, so that the calculation of ventilation rate should be based on the values for the ventilators open.(2) Pressure coefficients of side ventilator were dependent only on wind direction, not on angle of opening. The maximum value of 0.3 was observed at the wind angles of 0-30° and the minimum value of -0.4 at the wind angles of 150-180°. It was assumed that the wind angle is 0° when the wind blows perpendicular to the ridge line facing the ventilator open.(3) When only one side of ridge ventilators was open, pressure coefficients of the ventilator showed similar patterns to those of side ventilator, although the absolute values of them on the windward side increased slightly with increasing angle of opening. The minimum value of -0.4 was obtained at the wind angle of 135°(4) When both ridge ventilators were open, pressure coefficients of the ventilators were negative at any wind angle and angle of opening, and dependent on both wind direction and angle of opening. The minimum value was -0.4 at the wind angle of 30° when the ventilators were positioned horizontally.(5) Pressure coefficients of entrance/exit at gable end changed from -0.5 to 0.6 with the change of wind angle of 0 to 90° on the windward side, and on the leeward side they were -0.2 at the wind angles larger than 30°.(6) Discharge coefficients of ventilators under windless condition were approximately 0.1, 0.4 and 0.6 at the angles of opening 10, 30 and 50°, respectively, and that of entrance/exit at gable end was 0.7. However, those values changed slightly with the differences in types and mounted positions of ventilators.(7) Due to the influences of circumambient wind around the greenhouse, discharge coefficients changed with the change of wind direction and ν/V (mean air speed through opening to wind speed ratio). They reached the same values as those under windless condition with the increase of ν/V.(8) Discharge coefficients of side ventilator and entrance/exit at gable end were independent of wind direction and ν/V.(9) When only one side of ridge ventilators was open, discharge coefficients of the ventilator were dependent both on wind direction and ν/V at the angles of opening larger than 30°.(10) When both ridge ventilators were open, discharge coefficients of the ventilators were notably dependent on wind direction and ν/V, and the maximum values were observed at the wind

Field Measurements of the Benefits of Increased Stack Height

Analysis of a series of 31 field diffusion experiments permitted direct specification of the benefit of increased stack height. In the experiments, two tracers were released simultaneously from two different elevations on a 122 m tower, and were sampled at ground level on a series of arcs concentric about the release point. The ratio of observed concentrations at any sampling distance provides a measure of stack height benefits which is unobscured by differences in meteorology between experiments. Three combinations of upper/lower release elevations were used: 26 m/2 m, 56 m/26 m and 111 m/56 m. Over the 10 km range of field measurements, ground-level concentration ratios (upper source origin/lower source origin) were larger than similar ratios computed using observed meteorology and a Gaussian plume model. Since a larger ratio implies smaller benefits from increased stack height, the Gaussian model over-emphasized the benefits resulting from increased stack height. In a plume with minimal initial rise, there is a dilution at stack exit which is directly proportional to the wind speed at the top of the stack. At distances relatively far from the source, the benefits in reduced concentration resulting from increasing source height from 26 m to 56 m were found to plateau at approximately the ratio of wind speeds at the 26 and 56 m levels. Benefits accruing as a result of increasing from 56 m to 111 m exceeded the wind speed ratio at all distances. Conversely, benefits for an increase from 2 m to 26 m were lacking at distances beyond about 4 km.

Forest and Airport Wind Speeds

Abstract A simple equation is developed for determining the ratio of wind speed above a rough vegetative canopy, such as a forest, to the wind speed over a relatively smooth surface, such as an airport, when both sites are subject to the same geostrophic wind. The usual assumptions for simplifying flow in the planetary boundary layer are followed and appropriate canopy parameters are introduced. Values for the ratio of forest to airport wind speeds range from 0.4 to 0.7, with a typical value of 0.5.

The application of a 2-D convective cloud model to waste heat release from proposed nuclear energy centers

A two-dimensional time-dependent convective cloud model is applied to the problem of atmospheric effects from latent and sensible heat releases by nuclear energy centers. In the model applications the horizontal extent and strength of the source (perturbation) is consistent with those proposed for such centers. One case considers the effect of excess water vapor from such centers upon an existing squall line convective element which passes over the center. Other cases consider the initiation of convection by both latent and sensible heat consistent with that released by evaporative cooling towers in such a center. In the case of enhancement of existing convection the increases in maximum vertical wind speed and maximum rainwater mixing ratio within the storm are computed to be less than 10%. In the cloud initiation cases, sub-cloud layer stability variations in a Nashville, Tennessee sounding were considered with no variation in the environmental motion field. No deep convection occurred in a case where thermal stability was present between 0.4 and 1.6 km. In a case where the atmosphere was dry adiabatic in this layer, deep convection did occur. In another case where the same sounding included a nocturnal inversion, deep convection occurred but was delayed by 3–4 h. In a case utilizing a sounding characteristic of very hot conditions in the interior Pacific Northwest, no condensed cloud was produced. A brief discussion is presented concerning some of the serious problems involved in applying one-, two-and three-dimensional convective cloud models to the waste heat problem. Also, certain additional experiments are suggested for both the enhancement and the initiation cases.