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Ralph G. Eldridge

Abstract

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Ralph G. Eldridge

Abstract

Climatological visibility data for fifty-three sites is used to evolve seasonal visibility maps of the United States. The analysis is presented in the form of cumulative visibility frequency distribution maps. A brief discussion of their use and limitations to describe atmospheric opacity is included.

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Ralph G. Eldridge

Abstract

An analytical technique employing a fog drop-size distribution model is used to demonstrate the importance of the width of measured drop-size distributions when evolving a visibility-liquid water content relationship. Consistency is achieved between two apparently different visibility-liquid water content curves generated from two sets of fog drop-size distributions with this analysis.

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Ralph G. Eldridge

Abstract

An independent calibration of an instrument called a Particle Counter and the resulting fog drop-size distributions are discussed. The distributions exhibit an increasing number of droplets with decreasing size. The magnitude of the sampling error inherent in the instrument is inferred from a speculative argument based on the optical properties of measured drop-size distributions.

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Ralph G. Eldridge

Abstract

Through the analysis of infrared transmittance of a natural cloud, its drop-size distribution can be inferred. This technique has been used to measure and analyze ten cloud situations on Mount Washington. These clouds show drop-size distributions that are bimodal in character. In all the distributions, a large number of small droplets is inferred. To test the synthesized distributions in another region of the spectrum, the visual range was computed. This determination of the visual range is in agreement with the observed visibilities.

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Ralph G. Eldridge

Abstract

Spectral attenuation measurements through haze and fogs are used to synthesize aerosol distributions characteristic of the attenuating medium. Twelve fog drop-size distributions have been averaged into two general types of fogs for comparison with measured fog drop-size distributions and with a distribution predicted by theory. Seven time-phased fog drop-size distributions are used to illustrate the phenomena of droplet growth and fog degeneration. Finally, an empirical relationship between liquid water content and visual range is presented.

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Ralph G. Eldridge

The transition from haze to fog is manifest by the occurrence of dissimilar optical phenomena which are a consequence of a change in the aerosol distribution of the scattering medium. Based on these effects, visibilities between 0.5 and 1 km are properly called mist. Visibilities in excess of 1 km are, generally, characteristic of haze; whereas, fog is limited to visibilities less than 0.5 km.

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