Search Results

You are looking at 1 - 4 of 4 items for :

  • Author or Editor: J. C. Wyngaard x
  • Journal of Applied Meteorology and Climatology x
  • Refine by Access: All Content x
Clear All Modify Search
J. C. Wyngaard

Abstract

We present a theory for probe-induced flow distortion which is applicable in the atmosphere at heights greater than about 10 times the obstacle size. We use the theory to calculate the behavior of Reynolds shear stress and velocity variances ahead of a cylinder and a sphere. The stress is found to be most seriously distorted, the extent depending on the nature of the trailing wake. We show that the linear form of the theory should be adequate for most surface-layer applications, and we discuss how the theory can be applied to more complex geometries. We show that the “tilt correction” approach to the problem, which has been used by some workers, is incorrect in principle since it violates vorticity conservation, and is not even a good approximation in general.

Full access
J. C. Wyngaard and J. L. Lumley

Abstract

Design data and experimental results are presented for an eight-pole optimally flat filter which makes available the first seven derivatives of the filtered input signal.

Full access
J. C. Kaimal, J. C. Wyngaard, and D. A. Haugen

Abstract

The paper describes the general characteristics of a non-orthogonal sonic anemometer array. The effects of line-averaging and spatial separation (between mid-points of the horizontal paths) are analyzed and spatial transfer functions are derived for power spectra of the longitudinal, lateral and vertical velocity components. While line-averaging always causes spectral attenuation at wavenumbers larger than 1/l (where l is the sonic path length), spatial separation produces cross-contamination between the horizontal velocity spectra at wavenumbers exceeding 1/d (where d is the separation distance). For an array with a 120° angle between the horizontal sonic paths the net effect of this cross-contamination is to overestimate the longitudinal velocity spectrum and underestimate the lateral velocity spectrum. The separation distance which yields maximum flatness in the transfer function for the longitudinal component is found to be 0.6 l.

Also discussed are the effects of aliasing and long-term trends on the shape of the computed spectrum and spectral correction for the spatial transfer function in the context of these effects.

Full access
Leonard J. Peltier, Sue Ellen Haupt, John C. Wyngaard, David R. Stauffer, Aijun Deng, Jared A. Lee, Kerrie J. Long, and Andrew J. Annunzio

Abstract

A parameterization of numerical weather prediction uncertainty is presented for use by atmospheric transport and dispersion models. The theoretical development applies Taylor dispersion concepts to diagnose dispersion metrics from numerical wind field ensembles, where the ensemble variability approximates the wind field uncertainty. This analysis identifies persistent wind direction differences in the wind field ensemble as a leading source of enhanced “virtual” dispersion, and thus enhanced uncertainty for the ensemble-mean contaminant plume. This dispersion is characterized by the Lagrangian integral time scale for the grid-resolved, large-scale, “outer” flow that is imposed through the initial and boundary conditions and by the ensemble deviation-velocity variance. Excellent agreement is demonstrated between an explicit ensemble-mean contaminant plume generated from a Gaussian plume model applied to the individual wind field ensemble members and the modeled ensemble-mean plume formed from the one Gaussian plume simulation enhanced with the new ensemble dispersion metrics.

Full access