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J. M. Wilczak and Joost A. Businger

Abstract

A method is developed for retrieving turbulent pressure fluctuations from tower measurements of velocity and temperature, through use of the equations of motion. This method is applied to a series of large-scale eddies which are defined by their characteristic temperature ramp structure. The variance of pressure is found to follow local free-convection.

Large-scale eddy (LSE) pressure fields are used to estimate the pressure transport and pressure-gradient interaction terms in the convective surface-layer budgets of heat flux, stress and turbulent kinetic energy. The LSE pressure terms are found to balance the budgets to within 20–30% of the size of the largest budget terms.

Ensemble fields are formed by averaging individual LSE pressure transport and pressure-gradient interaction fields. The basic characteristics of these ensemble pressure covariance fields are easily related to the cross-products of the ensemble fields of p′, ∂p′/∂x, w′, and so on. This offers a simple way of visualizing the source of the budget pressure covariances in terms of the average LSE structure.

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S. E. Larsen, F. W. Weller, and J. A. Businger

Abstract

A continuous wave sonic anemometer-thermometer has been developed for simultaneous measurements of vertical velocity and temperature. The phase angle fluctuations are detected by means of a monolithic integrated phase-locked loop, the latter feature providing for inexpensive and accurate electronics. The principle is described and discussed.

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V. E. Suomi, J. A. Businger, and P. M. Kuhn

Abstract

No Abstract Available.

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J. A. Businger, M. Miyake, A. J. Dyer, and E. F. Bradley

Abstract

The results of a heat flux comparison experiment carried out at Hay, New South Wales, Australia, during May 1966 using a sonic anemometer thermometer (SAT), Fluxatron and Evapotron are reported. The instruments agree with each other to within a factor of 2 for individual runs. The large fluctuations from run to run of the individual estimates are mainly caused by the fact that the Eulerian point average does not provide an adequate statistical sample of the heat flux. This point is illustrated by the non-stationary behavior of the instantaneous product of vertical wind and temperature. As auxiliary results, values of σ w/u * and σ T/T * have been obtained which are somewhat higher than, but in general agreement with, observations reported by Mordukhovich and Zwang.

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S. F. Zhang, J. C. Wyngaard, J. A. Businger, and S. P. Oncley

Abstract

A new sonic anemometer, called the U.W. sonic anemometer, has been designed to minimize the flow distortion due to the transducer wakes. We present a general analytical model for calculating the effect of these transducer wakes on measured velocity spectra, and show that the effects in the U.W. sonic anemometer are indeed less than in conventional arrays. We suggest a method of correcting for the errors caused by the transducer wakes.

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J. A. Businger, J. C. Wyngaard, Y. Izumi, and E. F. Bradley

Abstract

Wind and temperature profiles for a wide range of stability conditions have been analyzed in the context of Monin-Obukhov similarity theory. Direct measurements of heat and momentum fluxes enabled determination of the Obukhov length L, a key independent variable in the steady-state, horizontally homogeneous, atmospheric surface layer. The free constants in several interpolation formulas can be adjusted to give excellent fits to the wind and temperature gradient data. The behavior of the gradients under neutral conditions is unusual, however, and indicates that von Kármán's constant is ∼0.35, rather than 0.40 as usually assumed, and that the ratio of eddy diffusivities for heat and momentum at neutrality is ∼1.35, compared to the often-suggested value of 1.0. The gradient Richardson number, computed from the profiles, and the Obukhov stability parameter z/L, computed from the measured fluxes, are found to be related approximately linearly under unstable conditions. For stable conditions the Richard on number approaches a limit of ∼0.21 as stability increases. A comparison between profile-derived and measured fluxes shows good agreement over the entire stability range of the observations.

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J. C. Kaimal, R. A. Eversole, D. H. Lenschow, B. B. Stankov, P. H. Kahn, and J. A. Businger

Abstract

The paper describes a convective boundary layer experiment conducted in April 1978 at the Boulder Atmospheric Observatory, and examines the spectral behavior of wind velocity and temperature from the Observatory's 300 m tower, from aircraft flights alongside the tower and from a surface network of anemometers, for evidence of terrain influence on turbulence structure. The gently rolling terrain at the site does not seem to affect the turbulence spectra from the tower in any perceptible manner, except for minor shifts in the vertical velocity and temperature spectral peaks. The aircraft vertical velocity spectra showed different shapes for alongwind and crosswind sampling directions, as in earlier measurements over ocean surfaces, and their peaks are displaced to higher wavenumbers compared with the tower spectra. Long-term spectra of horizontal wind components from surface stations around the tower exhibit no particular sensitivity to site selection. Under near-stationary conditions the peak of the spectrum of the streamwise component tends to reflect more closely the predominant boundary layer. convective scales than does the peak of the lateral wind component. The problem of identifying those scales in the presence of large shifts in wind direction is discussed.

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J. A. Businger, W. F. Dabberdt, A. C. Delany, T. W. Horst, C. L. Martin, S. P. Oncley, and S. R. Semmer

The Atmosphere-Surface Turbulent Exchange Research (ASTER) facility developed at the National Center for Atmospheric Research (NCAR) will support observational research on the structure of the atmospheric surface layer. ASTER will provide state-of-the-art measurements of surface fluxes of momentum, sensible heat, and water vapor, and support measurements of surface fluxes of trace chemical species. The facility will be available to the scientific community in the spring of 1990. The motivation for the development of ASTER and the elements that constitute this new national facility are briefly discussed.

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