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Earl E. Gossard

Seasonal charts of air-sea difference in refractive index are presented for the Mediterranean and Southeast Asia areas. The charts are discussed briefly in terms of the climatic regimes of the area, and applications to extended radar coverage are suggested.

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Earl E. Gossard

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No abstract available.

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Earl E. Gossard

Abstract

Two theoretical models of shear layers in the atmosphere are examined. The conditions for their dynamic stability are found and their predictions of wavelength to layer-thickness ratio are compared with classical models and with available observational data. Although the models are only rigorously applicable to in-compressible fluids, it is suggested that they also represent conditions in the atmosphere, and clear-air returns published by Katz from the high-power pulse radar at Wallops Island are especially emphasized. Model 2 appears to be able to account for the narrow band characteristic of many of the observed events and also to explain better than other models the observed wavelength to layer-thickness ratios.

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Earl E. Gossard

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The advent of Doppler clear-air radars for wind-height profiling opens the way for their use in a variety of other applications. This paper uses knowledge of the clear-air Doppler spectrum from a zenith-pointing radar together with the measured water droplet Doppler vertical velocity spectrum to calculate spectra of drop number density through clouds of droplets having substantial fall velocity. The method has been applied by Japanese scientist to measure drop-size distributions of precipitation particles from data acquired at the VHF MU radar facility. Here the method is applied to records obtained with a 915 MHz wind profiler located at Denver, Colorado, and the resulting spectra are presented and compared with the spectra that would have been obtained if the clear-air information were ignored. From the number density drop-size distribution, the corresponding liquid water distribution can be calculated. It is concluded that failure to take into account turbulence in the medium can result in order-of-magnitude errors in number density and liquid water. The requirements and limitations of a radar remote sensing drop spectrometer are discussed.

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Earl E. Gossard

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A new technique is examined for using Doppler radars to extract information about the size spectrum of cloud droplets too small to have terminal velocities large enough to be resolvable by the radar. If the drops are very small, motions of the drops are dominated by turbulent fluctuations in the medium rather than their fall velocity. Their motion is then the convolution of the terminal velocity with the turbulent velocity probability density function, and size information about the population can be obtained only by deconvolving the spectra. Doppler radars can extract this velocity and size information, as well as cloud liquid and liquid flux, using a surprisingly simple and accurate technique assuming some functional form (e.g., gamma) for the drop number density spectrum. The method also allows Doppler radars to extract drop size information independent of up-/downdrafts in the medium in which they are embedded. Various gamma and lognormal functions are compared, and finally, a “Stokes range” of drop sizes is added and found to he important. Examples are shown and errors are discussed.

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E. E. Gossard and W. B. Sweezy

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This paper describes a method for obtaining the dispersion properties of atmospheric waves from ground-based measurements of pressure and wind fluctuations. Having found the wave dispersion, we can find the displacement spectra of the waves aloft, making only minimal assumptions about the atmospheric model and, without having very accurate sounding information.

We have applied the method to a pair of events for which we had fairly complete documentation. In one case, the waves aloft were observed with a vertically-pointing, high-resolution FM-CW radar, and we have compared the observed vertical displacement spectra with those deduced from ground measurements. In another case, the waves were associated with a weather front and a nearby tropical storm. The ground measurements permitted us to deduce the history of the waves aloft, and we found that the wave system before passage of the front differed dramatically from the waves present after frontal passage.

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E. E. Gossard and J. H. Richter

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A high-resolution, vertically pointing FM/CW radar is used to record internal gravity waves in the lower atmosphere. When the temperature inversion in the atmosphere is near the ground (measured in wavelengths of the gravity waves), the shape of the waves indicates that nonlinear effects become important. Examples of such waves are shown and their shape is discussed. Theoretical results of Hunt, based on the Stokes method of approximating the solutions for waves of finite amplitude, are used to compare observation with theory.

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B. B. Stankov, E. R. Westwater, and E. E. Gossard

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A method is presented to obtain a high-vertical-resolution humidity profile if the location and strength of only a few significant segments of the humidity gradient profile are known. The method is based on a previously developed statistical inversion technique coupled with moisture gradient information derived from wind profiler and the radiosonde temperature measurements. An existing retrieval algorithm uses an independent historical radiosonde-derived dataset and data from a two-channel microwave radiometer, standard surface meteorological instruments, and a lidar ceilometer. In this study, the possibility of constraining the statistical retrieval using measurements of significant moisture gradients derived from wind profiler signals and radiosonde temperature observations is investigated. An example is given to illustrate the method: on 26 May 1994 the 449-MHz wind profiler/RASS at Erie, Colorado, detected a strong humidity gradient at 4.9 km MSL. A statistical inversion algorithm constrained to the radar-measured gradient at 4.9 km was used to estimate the moisture profile. Results from this example show that an improvement in retrieved humidity profiles in particular, in the strength and location of a shallow layer, can be obtained if only significant radar-sensed humidity gradient information is added to other ground-based remote sensing measurements.

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Willilam R. Moninger and Earl E. Gossard

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A model having smooth wind and density profiles, for which a new solution of the Taylor-Goldstein equation can be found, is described. This model is particularly suitable for comparison with the analogous piecewise linear model so that the influence of “corners” in profiles can be judged. Such corners are found in models studied by Rayleigh, Goldstein, Taylor, Howard, Holmboe, and Gossard.

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Earl E. Gossard and A. Shelby Frisch

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The relationship between the variances of temperature and vertical velocity fluctuations is examined experimentally and theoretically. Comparison of the variance data and the mean gradient data recorded on the 300 m tower at the Boulder Atmospheric Observatory leads to the conclusion that the remotely sensed ratio of the temperature and velocity variances offers hope of measuring gradients of temperature and radar refractive index from ground-based acoustic or radar clear-air sounders. Relationships in which temperature gradient depends only on the ratio of the variances of temperature and vertical velocity are found both from the flux equation and from the energy budget/temperature variance equations. From the two independent relations, a theoretical expression for Prandtl number versus Richardson number is found for a limited range of Richardson numbers. Finally, the character and magnitude of the influence of the stress and conductivity terms are estimated from the linearized problem, and solutions are found in terms of eddy viscosity and conductivity.

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