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- Author or Editor: Ben B. Balsley x
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Abstract
This paper shows that a very slight tilt of the vertically directed antenna beam of a VHF wind profiler can produce a measurable change in the observed long-term averaged “vertical” velocity profiles. The results are based primarily on data obtained using the NOAA/CU profiler at Piurn, Peru, where phase measurements of individual antenna elements made in 1992 showed that the calculated angle of the 3°-wide vertical beam was skewed only by about 0.06° from true vertical. This small error was corrected in February 1993 by carefully rephasing some of the array feedpoints. Mean vertical velocity profiles obtained prior to the correction were adjusted to account for the slight contamination by the horizontal wind. These corrected vertical profiles compare favorably with vertical profiles obtained after rephasing the antenna, as well as with mean vertical wind profiles from other profiler sites in our tropical Pacific profiler network.
The results show that in order to be confident in long-term averaged vertical wind profiles using VHF profilers in the Tropics, the vertically directed antenna needs to be very carefully phased. The results also suggest that long-term averaging tends to nullify any possible effects of apparent variations of the vertical beam that might arise from short-term echo specularity. In addition, asymmetric biases in the turbulent-scattering process thought to contaminate mean vertical velocity measurements at midlalitudes are not at all apparent in our tropical profiles. This final factor may be due to the much smaller average vertical velocity variances observed at low latitudes.
Abstract
This paper shows that a very slight tilt of the vertically directed antenna beam of a VHF wind profiler can produce a measurable change in the observed long-term averaged “vertical” velocity profiles. The results are based primarily on data obtained using the NOAA/CU profiler at Piurn, Peru, where phase measurements of individual antenna elements made in 1992 showed that the calculated angle of the 3°-wide vertical beam was skewed only by about 0.06° from true vertical. This small error was corrected in February 1993 by carefully rephasing some of the array feedpoints. Mean vertical velocity profiles obtained prior to the correction were adjusted to account for the slight contamination by the horizontal wind. These corrected vertical profiles compare favorably with vertical profiles obtained after rephasing the antenna, as well as with mean vertical wind profiles from other profiler sites in our tropical Pacific profiler network.
The results show that in order to be confident in long-term averaged vertical wind profiles using VHF profilers in the Tropics, the vertically directed antenna needs to be very carefully phased. The results also suggest that long-term averaging tends to nullify any possible effects of apparent variations of the vertical beam that might arise from short-term echo specularity. In addition, asymmetric biases in the turbulent-scattering process thought to contaminate mean vertical velocity measurements at midlalitudes are not at all apparent in our tropical profiles. This final factor may be due to the much smaller average vertical velocity variances observed at low latitudes.
Abstract
This note describes the development of a method for obtaining high vertical resolution (meter scale) measurements of basic meteorological quantities and turbulent overturns, using radiosondes with slow ascent rates. Although the method has some limitations, it can provide profiles of standard atmospheric variables from the surface to more than 20 km, with significantly improved vertical resolution. It can also help better identify regions of turbulent overturns. This correspondence presents some initial results demonstrating the occurrence of relatively small-vertical-scale overturns throughout the entire atmospheric column.
Abstract
This note describes the development of a method for obtaining high vertical resolution (meter scale) measurements of basic meteorological quantities and turbulent overturns, using radiosondes with slow ascent rates. Although the method has some limitations, it can provide profiles of standard atmospheric variables from the surface to more than 20 km, with significantly improved vertical resolution. It can also help better identify regions of turbulent overturns. This correspondence presents some initial results demonstrating the occurrence of relatively small-vertical-scale overturns throughout the entire atmospheric column.
Abstract
The DataHawk small airborne measurement system provides in situ atmospheric measurement capabilities for documenting scales as small as 1 m and can access reasonably large volumes in and above the atmospheric boundary layer at low cost. The design of the DataHawk system is described, beginning with the atmospheric measurement requirements, and articulating five key challenges that any practical measurement system must overcome. The resulting characteristics of the airborne and ground support components of the DataHawk system are outlined, along with its deployment, operating, and recovery modes. Typical results are presented to illustrate the types and quality of data provided by the current system, as well as the need for more of these finescale measurements. Particular focus is given to the DataHawk's ability to make very-high-resolution measurements of a variety of atmospheric variables simultaneously, with emphasis given to the measurement of two important finescale turbulence parameters, 
Abstract
The DataHawk small airborne measurement system provides in situ atmospheric measurement capabilities for documenting scales as small as 1 m and can access reasonably large volumes in and above the atmospheric boundary layer at low cost. The design of the DataHawk system is described, beginning with the atmospheric measurement requirements, and articulating five key challenges that any practical measurement system must overcome. The resulting characteristics of the airborne and ground support components of the DataHawk system are outlined, along with its deployment, operating, and recovery modes. Typical results are presented to illustrate the types and quality of data provided by the current system, as well as the need for more of these finescale measurements. Particular focus is given to the DataHawk's ability to make very-high-resolution measurements of a variety of atmospheric variables simultaneously, with emphasis given to the measurement of two important finescale turbulence parameters,
Abstract
The VHF Doppler radar has become a powerful tool for probing structures and motions of the clear air. In this paper, we discuss the capability of VHF radar as a tool for cloud and precipitation studies. Large fluctuations of refractive index from the cloudy air can be anticipated because of an abundance of water in clouds. Due to the difficulties in obtaining the necessary fine-scale observational data within clouds, we base our analysis of cloud-echoing properties on the numerical simulation of nonprecipitating cumulus by Klaassen and Clark. The Bragg scatter echo intensity is estimated from the temperature and humidity fields obtained from the cloud model. We find that the echo is enhanced at the boundary between the cloud and environment because of enhanced water vapor fluctuations. Although echoes from nonprecipitating clouds can be detected by UHF and VHF radars, only VHF radars can discriminate echoes due to large precipitation particles from the Bragg scatter echo of cloudy air. With UHF radars, the precipitation echoes totally mask the Brag scatter echoes.
Abstract
The VHF Doppler radar has become a powerful tool for probing structures and motions of the clear air. In this paper, we discuss the capability of VHF radar as a tool for cloud and precipitation studies. Large fluctuations of refractive index from the cloudy air can be anticipated because of an abundance of water in clouds. Due to the difficulties in obtaining the necessary fine-scale observational data within clouds, we base our analysis of cloud-echoing properties on the numerical simulation of nonprecipitating cumulus by Klaassen and Clark. The Bragg scatter echo intensity is estimated from the temperature and humidity fields obtained from the cloud model. We find that the echo is enhanced at the boundary between the cloud and environment because of enhanced water vapor fluctuations. Although echoes from nonprecipitating clouds can be detected by UHF and VHF radars, only VHF radars can discriminate echoes due to large precipitation particles from the Bragg scatter echo of cloudy air. With UHF radars, the precipitation echoes totally mask the Brag scatter echoes.
Fine Structure, Instabilities, and Turbulence in the Lower Atmosphere: High-Resolution In Situ Slant-Path Measurements with the DataHawk UAV and Comparisons with Numerical ModelingAbstract
A new platform for high-resolution in situ measurements in the lower troposphere is described and its capabilities are demonstrated. The platform is the small GPS-controlled DataHawk unmanned aerial system (UAS), and measurements were performed under stratified atmospheric conditions at Dugway Proving Ground, Utah, on 11 October 2012. The measurements included spiraling vertical profiles of temperature and horizontal wind vectors, from which the potential temperature θ, mechanical energy dissipation rate ε, Brunt–Väsälä frequency N, temperature structure parameter C T 2, Thorpe and Ozmidov scales L T and L O , and Richardson number Ri were inferred. Profiles of these quantities from ~50 to 400 m reveal apparent gravity wave modulation at larger scales, persistent sheet-and-layer structures at scales of ~30–100 m, and several layers exhibiting significant correlations of large ε, C T 2, L T , and small Ri. Smaller-scale flow features suggest local gravity waves and Kelvin–Helmholtz instabilities exhibiting strong correlations, yielding significant vertical displacements and inducing turbulence and mixing at smaller scales. Comparisons of these results with a direct numerical simulation (DNS) of similar multiscale dynamics indicate close agreement between measured and modeled layer character and evolution, small-scale dynamics, and turbulence intensities. In particular, a detailed examination of the potential biases in inferred quantities and/or misinterpretation of the underlying dynamics as a result of the specific DataHawk sampling trajectory is carried out using virtual sampling paths through the DNS and comparing these with the DataHawk measurements.
Abstract
A new platform for high-resolution in situ measurements in the lower troposphere is described and its capabilities are demonstrated. The platform is the small GPS-controlled DataHawk unmanned aerial system (UAS), and measurements were performed under stratified atmospheric conditions at Dugway Proving Ground, Utah, on 11 October 2012. The measurements included spiraling vertical profiles of temperature and horizontal wind vectors, from which the potential temperature θ, mechanical energy dissipation rate ε, Brunt–Väsälä frequency N, temperature structure parameter C T 2, Thorpe and Ozmidov scales L T and L O , and Richardson number Ri were inferred. Profiles of these quantities from ~50 to 400 m reveal apparent gravity wave modulation at larger scales, persistent sheet-and-layer structures at scales of ~30–100 m, and several layers exhibiting significant correlations of large ε, C T 2, L T , and small Ri. Smaller-scale flow features suggest local gravity waves and Kelvin–Helmholtz instabilities exhibiting strong correlations, yielding significant vertical displacements and inducing turbulence and mixing at smaller scales. Comparisons of these results with a direct numerical simulation (DNS) of similar multiscale dynamics indicate close agreement between measured and modeled layer character and evolution, small-scale dynamics, and turbulence intensities. In particular, a detailed examination of the potential biases in inferred quantities and/or misinterpretation of the underlying dynamics as a result of the specific DataHawk sampling trajectory is carried out using virtual sampling paths through the DNS and comparing these with the DataHawk measurements.
