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D. Keith Wilson
and
Dennis W. Thomson

Abstract

Acoustic tomography is proposed as a method for monitoring near-surface atmospheric temperature and wind velocity fields. Basic issues relating to the feasibility and implementation of atmospheric tomography are discussed. Among these issues are the causes of fluctuations in acoustic signals propagated through the atmosphere, appropriate spatial dimensions of an array, signal detection and processing techniques, mathematical inverse techniques and their numerical implementation, and whether or not tomography m provide measures of dynamical variables of interest to atmospheric scientists. Surface-layer, horizontal-slice tomography was implemented experimentally, with an array of three sources and seven receivers distributed over a region approximately 200 m square. Travel-time fluctuations at the receivers were used to reconstruct the temperature and wind fields with about 50-m resolution in the horizontal plane.

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B. Duan
,
C. W. Fairall
, and
D. W. Thomson

Abstract

Eddy correlation measurements of the vertical fluxes of particles, momentum, heat and water vapor, were conducted over a partially snow covered field in central Pennsylvania during December 1985. The PMS ASASP-300 and CSASP-100-HV optical counters were used as sensors to measure particle-number fluxes. Overall, average dry deposition velocities for 28 half-hour runs were found to be 0.034 ± 0.014 and 0.021 ± 0.005 cm s−1 for particles in two size ranges, 0.15–30 and 0.5–1.0 μm, respectively. The average deposition velocity was close to results from prior wind-tunnel and theoretical investigations. These results were also comparable with those reported by other authors over grass. Relatively large sampling rates reduced the effects of counting noise on deposition measurements of 0.5–;1.0 μm particles. Small correlation coefficients between vertical velocity and the particle concentration were found even after corrections for the effects of counting noise. The normalized average surface deposition velocity vds /u * for particles in diameter of 0.15–0.30 and 0.5–1.0 μm appeared to be 0.006 and 0.002, respectively, in nearly neutral and stable conditions.

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D. W. Thomson
and
J. P. Scheib

Improved quantitative display techniques, including digital false-color systems, for use with sodar or other similar remote probing systems are discussed. With sodar the use of a false-color system greatly facilitates real-time measurements of temperature and velocity structure functions, the dissipation rates of turbulent kinetic energy and temperature variance in the planetary boundary layer of the atmosphere, and the vertical wind and wind shear profiles.

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D. J. Thomson
,
W. L. Physick
, and
R. H. Maryon

Abstract

The problem of how to formulate random walk dispersion models in situations where the flow properties vary discontinuously across an interface is considered. It is shown how the dispersion model can be made consistent with the assumptions made about the turbulence. The approach does not lead to a unique model, but it is argued that in many cases the rate of diffusion through the interface is limited not by the detailed physics of the interface but by the rates of diffusion on either side of the interface and, in such situations, results may be insensitive to which of the consistent models is chosen. Some simulations are presented to illustrate these ideas.

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D. W. Thomson
,
R. L. Coulter
, and
Z. Warhaft

Abstract

Simultaneous measurements of C T 2 and C V 2 were made using a calibrated Doppler sodar and a research aircraft equipped with meteorological and turbulence sensors. In each experiment a region of specific interest was identified using the sodar and then the aircraft vectored into it using air-ground radio. Measurements were made in both “layers” (with and without detectable turbulence and “waves”) and in convective plumes. In each case the spectra of turbulent temperature and velocity fluctuations derived from the in situ observations showed a well-developed inertial subrange. Excellent agreement was found between the magnitude of the in situ aircraft C T 2 and C V 2 values and those derived from the sodar signals interpreted using the Tatarski scattering theory.

Examples are shown of how sodar may be used for real-time, quantitative estimates of the dissipation rate of turbulent kinetic energy ε, and the rate of destruction of temperature variance N. On the present Penn State sodar system the operator may select a display of C T 2 , C V 2 , ε, N or winds derived from signal Doppler shifts. Either time series at selected heights, vertical time sections on a color, digital video display, or conventional printed or graphical output may be produced.

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W. P. Kemp
,
D. G. Burnell
,
D. O. Everson
, and
A. J. Thomson

Abstract

Seven methods for estimating maximum and minimum temperatures were developed from the literature and other sources. These techniques include correlative and additive procedures based on the relationships between stations, as well as procedures based on within-station temperature relations. Selection of the most appropriate technique will depend on the ultimate purpose for which the data are to be used, the size of the gaps in the weather record, and the availability of data from other stations to include in the analysis. Within-and between-station methods were compared by looking at their relative abilities to predict “pseudo” missing data items from two groups of weather stations in northern and central Idaho. Between-station regression techniques generated significantly smaller errors when compared to the remaining methods. Application of one of the methods to stations in British Columbia that contain large gaps in weather records was also described.

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J. A. Reagan
,
J. D. Spinhirne
,
D. M. Byrne
,
D. W. Thomson
,
R. G. De Pena
, and
Y. Mamane

Abstract

Particulate size and height distributions, complex refractive index and mass loading have been measured and inferred from direct aircraft and indirect lidar-solar radiometer observations made during a unique joint experiment conducted the week of 18 November 1974 in Tucson, Ariz. The aircraft and lidar-solar radiometer measurements were first analyzed independently and the results were then intercompared. Vertical profiles of particulate extinction obtained from the lidar (monostatic) and aircraft measurements were found to be in excellent agreement on both a relative and absolute basis. Lidar (bistatic and monostatic) inferences of particulate mass loading agreed favorably with the aircraft mass monitor measurements. The aircraft and lidar (bistatic) size distribution determinations were found to be similar in shape and agreed in absolute value within an order of magnitude. The mean particle refractive index inferred from the lidar (bistatic) measurements (n = 1.40 − i0.000) agreed with the index of a significant fraction of the particles identified by electron microscope analysis of impactor samples collected with the aircraft.

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E. E. Clothiaux
,
R. S. Penc
,
D. W. Thomson
,
T. P. Ackerman
, and
S. R. Williams

Abstract

Algorithms for deriving winds from profiler range-gated spectra currently rely on consensus averaging to remove outliers from the subhourly velocity estimates. For persistent ground clutter in the echo return that is stronger than the atmospheric component, consensus averaging of the spectral peak power densities fails because the peak power density is derived from the ground clutter and not the atmosphere. To negate the deleterious effects of persistent ground clutter, as well as to attempt to improve performance during periods of poor signal-to-noise ratio, an algorithm was developed that uses the local maxima in power density in each spectrum to build multiple profiles of possible radial velocity estimates from the first to last range tale. To build profiles of radial velocity estimates from a set of spectra, the spectra are smoothed, the local power density maxima are identified, chains are formed across range gates by connecting those local power density maxima that satisfy a continuity constraint, and finally profiles are built from a combination of chains by maximizing an energy function based on continuity, gate separation, and summed power density. Features based on power density and power density after half-plane subtraction are then constructed for each profile and a backpropagation neural network is subsequently used to classify the profile most likely reflecting the atmospheric state. It was found that use of this technique significantly reduced ground clutter contamination in the horizontal beam velocity estimates and improved performance at low signal-to-noise ratios for all velocity estimates.

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Brian D. Pollard
,
Samir Khanna
,
Stephen J. Frasier
,
John C. Wyngaard
,
Dennis W. Thomson
, and
Robert E. McIntosh

Abstract

The local structure and evolution of the convective boundary layer (CBL) are studied through measurements obtained with a volume-imaging radar, the turbulent eddy profiler (TEP). TEP has the unique ability to image the temporal and spatial evolution of both the velocity field and the local refractive index structure-function parameter, 2 n . Volumetric images consisting of several thousand pixels are typically formed in as little as 1 s. Spatial resolutions are approximately 30 m by 30 m by 30 m.

CBL data obtained during an August 1996 deployment at Rocks Springs, Pennsylvania, are presented. Measurements of the vertical 2 n profile are shown, exhibiting the well-known bright band near the capping inversion at z i , as well as intermittent plumes of high 2 n . Horizontal profiles show coherent 100-m-scale 2 n and vertical velocity (w) structures that correspond to converging horizontal velocity vectors. To quantify the scales of structures, the vertical and streamwise horizontal correlation distances are calculated within the TEP field of view.

To study the statistics and scales of larger structures, effective volumes larger than the TEP field of view are constructed through Taylor’s hypothesis. Statistics of 2 n and w time series are compared to an appropriately scaled large eddy simulation (LES). While w time series comparisons agree very well, the LES 2 n predictions agree only with some of the measured data. Finally, the scales of 2 n structures in the TEP time series measurements are calculated and compared to the scales in the LES spatial domain. Good agreement is found only near the capping inversion layer, the area of largest structures. This study highlights the unique capabilities of the TEP instrument, and shows what are believed to be the first statistical comparisons of measured 2 n data with LES derived results.

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C. O. Collins III
,
B. Blomquist
,
O. Persson
,
B. Lund
,
W. E. Rogers
,
J. Thomson
,
D. Wang
,
M. Smith
,
M. Doble
,
P. Wadhams
,
A. Kohout
,
C. Fairall
, and
H. C. Graber

Abstract

“Sea State and Boundary Layer Physics of the Emerging Arctic Ocean” is an ongoing Departmental Research Initiative sponsored by the Office of Naval Research (http://www.apl.washington.edu/project/project.php?id=arctic_sea_state). The field component took place in the fall of 2015 within the Beaufort and Chukchi Seas and involved the deployment of a number of wave instruments, including a downward-looking Riegl laser rangefinder mounted on the foremast of the R/V Sikuliaq. Although time series measurements on a stationary vessel are thought to be accurate, an underway vessel introduces a Doppler shift to the observed wave spectrum. This Doppler shift is a function of the wavenumber vector and the velocity vector of the vessel. Of all the possible relative angles between wave direction and vessel heading, there are two main scenarios: 1) vessel steaming into waves and 2) vessel steaming with waves. Previous studies have considered only a subset of cases, and all were in scenario 1. This was likely to avoid ambiguities, which arise when the vessel is steaming with waves. This study addresses the ambiguities and analyzes arbitrary cases. In addition, a practical method is provided that is useful in situations when the vessel is changing speed or heading. These methods improved the laser rangefinder estimates of spectral shapes and peak parameters when compared to nearby buoys and a spectral wave model.

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