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- Author or Editor: J. C. Kaimal x
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Abstract
Data from a boundary-layer experiment conducted over a flat, uniform site in Minnesota provide a clue to the behavior of the low-frequency peak in surface-layer horizontal velocity spectra. This portion of the spectra shows systematic behavior only when plotted in dimensionless coordinates appropriate to the mixed layer, whereas the inertial subrange frequencies follow Monin-Obukhov similarity. Based on this observation, interpolation formulas for both the longitudinal and the lateral velocity components, are derived. The expressions involve the boundary-layer depth in addition to the usual surface-layer parameters.
Abstract
Data from a boundary-layer experiment conducted over a flat, uniform site in Minnesota provide a clue to the behavior of the low-frequency peak in surface-layer horizontal velocity spectra. This portion of the spectra shows systematic behavior only when plotted in dimensionless coordinates appropriate to the mixed layer, whereas the inertial subrange frequencies follow Monin-Obukhov similarity. Based on this observation, interpolation formulas for both the longitudinal and the lateral velocity components, are derived. The expressions involve the boundary-layer depth in addition to the usual surface-layer parameters.
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The Boulder Atmospheric Observatory (BAO) is a unique research facility for studying the planetary boundary layer and for testing and calibrating atmospheric sensors. The facility includes a 300 m tower instrumented with fast- and slow-response sensors, a variety of remote sensing systems, and a real-time processing and display capability that greatly reduces analysis time for scientists working with current or archived data. In the past four years of operation the BAO has been the site of several large cooperative experiments and numerous smaller ones. Details of the data acquisition, processing and archiving schemes are presented. Results of studies conducted and opportunities for future investigations are also described.
Abstract
The Boulder Atmospheric Observatory (BAO) is a unique research facility for studying the planetary boundary layer and for testing and calibrating atmospheric sensors. The facility includes a 300 m tower instrumented with fast- and slow-response sensors, a variety of remote sensing systems, and a real-time processing and display capability that greatly reduces analysis time for scientists working with current or archived data. In the past four years of operation the BAO has been the site of several large cooperative experiments and numerous smaller ones. Details of the data acquisition, processing and archiving schemes are presented. Results of studies conducted and opportunities for future investigations are also described.
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A sonic anemometer-thermometer, based on transmission of continuous sound waves and determination of phase angle variations, has been developed. The instrument is designed to measure the fluctuations in the vertical wind component and temperature simultaneously. Measurement of these two quantities enables one to determine the eddy heat flux in the turbulent boundary layer. Field tests indicate that the instrument performs satisfactorily.
Abstract
A sonic anemometer-thermometer, based on transmission of continuous sound waves and determination of phase angle variations, has been developed. The instrument is designed to measure the fluctuations in the vertical wind component and temperature simultaneously. Measurement of these two quantities enables one to determine the eddy heat flux in the turbulent boundary layer. Field tests indicate that the instrument performs satisfactorily.
Abstract
The paper describes the characteristics of a convective plume and a dust devil from measurements made at 5.66 and 22.6 m above a flat uniform site in Kansas. The velocity fluctuations were measured with a continuous-wave, three-component sonic anemometer and the temperature fluctuations with a fine platinum wire thermometer. The data show that the plume is basically a non-rotating system; it is more tilted in the downwind direction than the dust devil, travels at a lower velocity than the mean wind speed at 0.5 m, and requires vertical stretching for its maintenance in the presence of wind shear. The dust devil shows a down-draft in the middle, travels at a higher velocity than the mean wind at 32 m, and derives much of its stability from rotation. Both systems tend to transport momentum upward, against the velocity gradient, which probably accounts for the very low and sometimes negative stresses observed during unstable conditions.
Abstract
The paper describes the characteristics of a convective plume and a dust devil from measurements made at 5.66 and 22.6 m above a flat uniform site in Kansas. The velocity fluctuations were measured with a continuous-wave, three-component sonic anemometer and the temperature fluctuations with a fine platinum wire thermometer. The data show that the plume is basically a non-rotating system; it is more tilted in the downwind direction than the dust devil, travels at a lower velocity than the mean wind speed at 0.5 m, and requires vertical stretching for its maintenance in the presence of wind shear. The dust devil shows a down-draft in the middle, travels at a higher velocity than the mean wind at 32 m, and derives much of its stability from rotation. Both systems tend to transport momentum upward, against the velocity gradient, which probably accounts for the very low and sometimes negative stresses observed during unstable conditions.
Abstract
A simplified acoustic Doppler wind sensor that can be built around an existing sounder is described. The instrument consists of two fan-beam transmitters and a pencil-beam receiver in an orthogonal configuration. Considerable improvement in signal-to-noise ratio over previous techniques is realized with this approach. Field tests show good agreement between the Doppler sounder measurements and wind measurements with in situ sensors on a 150 m tower. The system operated satisfactorily in an airport environment under fog conditions as well as in light rain. It failed only during periods of jet aircraft activity directly over the sounder and under conditions of moderate-to-heavy rainfall.
Abstract
A simplified acoustic Doppler wind sensor that can be built around an existing sounder is described. The instrument consists of two fan-beam transmitters and a pencil-beam receiver in an orthogonal configuration. Considerable improvement in signal-to-noise ratio over previous techniques is realized with this approach. Field tests show good agreement between the Doppler sounder measurements and wind measurements with in situ sensors on a 150 m tower. The system operated satisfactorily in an airport environment under fog conditions as well as in light rain. It failed only during periods of jet aircraft activity directly over the sounder and under conditions of moderate-to-heavy rainfall.
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Sonic anemometers were installed at four levels on the Cedar Hill television tower and operated for selected periods during three weeks in August 1963. One of the runs covered the entire history of a nocturnal low-level jet. The vertical velocity fluctuations measured by the sonic anemometers are examined closely for their relationship to mean horizontal wind speed and temperature profiles obtained from existing meteorological instrumentation on the tower. In a qualitative sense the data confirm many of the current speculations on the role of turbulence in the development and dissipation of these jets. Statistical analysis of the fluctuation data provides some interesting results, particularly for the period following breakdown of the surface inversion. The constant of proportionality between standard deviation of the vertical velocity component at 150 ft and friction velocity is found to be 1.22. The limiting value of Richardson number for maintenance of an inversion at 450 ft appears to be 0.25.
Abstract
Sonic anemometers were installed at four levels on the Cedar Hill television tower and operated for selected periods during three weeks in August 1963. One of the runs covered the entire history of a nocturnal low-level jet. The vertical velocity fluctuations measured by the sonic anemometers are examined closely for their relationship to mean horizontal wind speed and temperature profiles obtained from existing meteorological instrumentation on the tower. In a qualitative sense the data confirm many of the current speculations on the role of turbulence in the development and dissipation of these jets. Statistical analysis of the fluctuation data provides some interesting results, particularly for the period following breakdown of the surface inversion. The constant of proportionality between standard deviation of the vertical velocity component at 150 ft and friction velocity is found to be 1.22. The limiting value of Richardson number for maintenance of an inversion at 450 ft appears to be 0.25.
