A study of the deviations of wind speeds and directions from geostrophic values

Godson, W. L.

doi:10.1002/qj.49707632703

Cited by 13 publications

(8 citation statements)

References 6 publications

(5 reference statements)

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“…I n summer, lDagl decreases with both increasing actual and geostrophic wind speed, and large values of occur at higher levels and with lower wind speeds. Theoretically, the angle between geostrophic wind and actual wind direction is inversely proportional to geostrophic wind speed [see Godson (1950) for the discussion of this relation]. The results obtained in this study verify this theoretical prediction for geostrophic wind speeds less than 40 m/s.…”

Section: Apparent Geostrophic Deviationsupporting

confidence: 81%

“…Method C differs from methods A and B in that geostrophic deviations are determined from accelerations without recourse to pressure-height data. The accelerations are determined either from constant-pressure balloon trajectory data as has been done by Neiburger and Angel1 (1956) and Giles and Peterson (1957), or by evaluating local time-and space variations of wind speed and direction, using observed wind data (Godson 1950). It also includes a technique by which geostrophic winds are computed from observed winds using the balance equation (Endlich 1968).…”

Section: Deviation Can Be Broadly Classified Into Methods a B Andmentioning

confidence: 99%

“…Results from a study of geostrophic deviation at 10,000 ft by Godson (1950) revealed that large deviation angles were associated with low geostrophic wind speeds. One of the conclusions from Neiburger and Angell's (1956) study is that (at the 300-mb level) the average angle between actual and geostrophic wind vanes inversely with actual wind speed.…”

Section: Apparent Geostrophic Deviationmentioning

confidence: 99%

“…On the average for both summer and winter, this difference is about 1.8 w/s at the 500-mb level, about 4 m/s at the 150-mb level, and about 7 m/s at the 20-mb level. Previous studies yielded, for 10,000 ft., a mean value of absolute speed deviation of the order of 3.6 m/s (Godson 1950) and a mean value of absolute vector wind deviation of 4.8 m/s (Houghton and Austin 1946). Godson's study ---also gave an average value of 15' for the mean absolute direction deviation.…”

Section: Apparent Geostrophic Deviationmentioning

confidence: 99%

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Geostrophic Wind Deviation in the Upper Troposphere and lower Stratosphere in the El Paso–White Sands Area

Jehn

1972

Mon. Wea. Rev.

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Wind data at and above the 500-mb level taken from the El Paso, Tex., rawinsonde Station (rawin) and pressure-height data at the same levels from Albuquerque, N. Mex., Midland, Tex., Tucson, Ariz., and Chihuahua, Mexico, during the 1965-66 winter and the 1966 summer periods were used t o study geostrophic wind deviation. Geostrophic winds were computed directly from the pressure-height data by a finite-difference method and compared to the actual wind as measured at El Paso. The variations of the "apparent" geostrophic wind deviation with wind speed and pressure-height were examined. Errors involved were analyzed and the "true" geostrophic wind deviation and the total wind accelerations were estimated. Results of the study reveal: (1) that despite the improvement in the accuracies of the radiosonde pressure-height and rawin data, the errors in the data still account for a large portion of the apparent geostrophic wind deviation at higher levels (at and above the 150-mb level) ; (2) that to use the geostrophic wind approximation in cases with wind speed less than 20 m/s would probably result in vector wind errors of the order of 40 percent or more; and (3) that the mean true geostrophic wind deviation increases when the mean actual wind speed increases, and the estimated mean total wind accelerations range from 1 X 10" to 5 X lo-' m.s-' at and above the 500-mb level.

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Section: Apparent Geostrophic Deviationsupporting

confidence: 81%

Section: Deviation Can Be Broadly Classified Into Methods a B Andmentioning

confidence: 99%

Section: Apparent Geostrophic Deviationmentioning

confidence: 99%

Section: Apparent Geostrophic Deviationmentioning

confidence: 99%

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Geostrophic Wind Deviation in the Upper Troposphere and lower Stratosphere in the El Paso–White Sands Area

Jehn

1972

Mon. Wea. Rev.

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“…Arnold [1] derived a value for representativeness of double-theodolite wind observations by tracking two balloons released simultaneously ; the average difference in wind speeds of the two balloons was slightly more than 1 mph. Godson [4] determined daily changes in wind velocity to be 41 mph for 618 cases, most of which can probably be accounted for by largescale day-to-day changes in general flow patterns. While this variation is much larger than would be predicted from the present study, the difference may be attributable to differences in behavior of air masses over southwestern United States and England.…”

mentioning

confidence: 99%

The Representativeness of Winds-Aloft Observations

Reed

1954

Bulletin of the American Meteorological Society

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By using radar winds accurate to ± 2 fps the hourly turbulent wind variation is found to be approximately ± 6 fps. This limitation is then used to determine optimum procedures for both observing and forecasting accuracy. METEOROLOGISTS are always confronted with the problem of providing "best possible" forecasts and observations. Making the best possible observation is usually considered strictly a problem in instrumentation, and for winds-aloft observations it is usually resolved by using bigger and better radars, more theodolites, or taking more readings.Little effort has been made to evaluate the significance of limitations placed by inherent turbulence on attempts to measure atmospheric structure. Minimum errors introduced by this turbulence limitation may be approximated by subtracting known instrumental variations from the total deviations of a large number of observations from their mean over a representative period of time. Such an approach to the problem has been used in this study.Arnold [1] found that for upper winds measured by radar (rawin), errors in velocity averaged 4.2 fps, which corresponds to a standard error of about 5.1 fps. He also found the average instrumental accuracy of the two-theodolite method of tracking balloons to be ± 0.8 fps.The rawin installation operated by Sandia Laboratory at Salton Sea Test Base, California, and used for this series of measurements, was no ordinary installation, however. A considerably modified SCR-584 radar, permanently installed and oriented, was used in conjunction with an MPQ-2A RC305 PT61/UP automatic plotting board. Test runs were made on 21 and 23 February 1950 to check the accuracy of the rawin installation against a four-station precision range of Askania phototheodolites. To about 9000 feet MSL the standard deviation of the vector error of the rawin observations was found to be approximately ± 2 fps. Balloon locations were recorded every ten seconds. Horizontal coordinate differences at 30-sec. intervals were determined to give a mean wind for each level. Errors were almost the same for both component directions and varied little from day to day.A radar system for observing wind velocities to 40,000 feet can handle only one balloon ascension an hour. To obtain the data on which this analysis is based a series of ascensions of four to FIG. 1. Wind-trend approximation method.

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Determining Geostrophic Winds Using a Satellite‐borne Infra‐red Radiometer

Alexander¹

1976

Weather

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White Sands Missile Range, New MexicoETERMINING the wind field using current satellite instrumentation is very D difficult even under optimum conditions. Two techniques at present receiving much attention are the inference of winds by clouds or moist tongue motion (via visible and infra-red data) and the use of the correspondence between sea-surface wind and the height of sea waves, the latter being inferred from the reflectivity of the sea surface in the visible or the emissivity of the sea surface in the microwave (Ohring 1972). These techniques are primarily limited by the availability of suitable cloud tracers in the first case and to retrieving only seasurface winds in the other. Other obvious problems include the apparent motion of clouds caused by dissipation and building and the difficulty of accurately determining cloud height to locate the winds vertically.It appears feasible that a useful approximation to the wind field for much of the atmosphere might be calculated from data obtained by those satellitebased infra-red radiometers that are specifically designed to sound the atmospheric thermal structure. The wind that might be obtained using such instruments is the geostrophic wind, which provides a reasonable approximation to the actual wind for a wide range of probable meteorological conditions for latitudes greater than 10"-20" north or south and altitudes greater than 1-2 km. THE GEOSTROPHIC APPROXIMATIONIn the geostrophic approximation it is assumed that the significant horizontal forces in the atmosphere are the pressure gradient and Coriolis forces, and that these forces are in equilibrium. Thus, the geostrophic wind resulting from these approximations is given by (see Holton 1972) + where k is the unit vertical vector, p is the density, ,,p is the horizontal pressure gradient, and f=2Q sin 4, the Coriolis parameter (where Q and q5 are the angular velocity of the earth and the latitude, respectively). Another useful form of the geostrophic equation is easily obtained from (1) and the hydrostatic equation : g-Vg =-k X VpZ, f -rwhere Z is the geopotential height, g is the acceleration due to gravity, and D is the gradient along constant pressure surfaces. 191

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A study of the deviations of wind speeds and directions from geostrophic values

Cited by 13 publications

References 6 publications

Geostrophic Wind Deviation in the Upper Troposphere and lower Stratosphere in the El Paso–White Sands Area

Geostrophic Wind Deviation in the Upper Troposphere and lower Stratosphere in the El Paso–White Sands Area

The Representativeness of Winds-Aloft Observations

Determining Geostrophic Winds Using a Satellite‐borne Infra‐red Radiometer

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