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G. Garland Lala and James E. Jiusto

Abstract

A one-dimensional model was developed to examine humidity fields within a conditioning chamber for measuring ice nucleus concentrations on millipore filters. Representative concentrations of ice and cloud condensation nuclei were assumed, and the interplay among these growing particles (vapor sinks), the supply flux of vapor, and the resultant relative humidity at and above the filter surface investigated.

The model suggests that water saturation is not achieved under typical operating conditions of such chambers. Maximum humidifies reached decrease with increasing numbers of either condensation or ice nuclei, thereby offering another possible explanation of the filter volume effect. Most favorable operating conditions for achieving highest chamber humidities are delineated. The results suggest that this technique is capable of detecting mixed condensation-freezing nuclei, deposition nuclei and some contact nuclei, with the former perhaps being most common not only in filter measurements but also in the atmosphere.

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Alfred H. Woodcock, Duncan C. Blanchard, and James E. Jiusto

Abstract

In Past 1 of this fog study, the distribution of water with number and size of drops in some New England marine advection fogs was shown to be related to the distribution of number and size of salt particles found in marine air. It was indicated that in saturated air the calculated amounts of water condensed on the salt particles produced water distributions as a function of drop size much like distributions observed in numerous advection fogs. The results suggest that salt particles play an important role in the initiation and growth of marine fogs.

In the present work, photomicrographs of drops and of drop salt nuclei from several New England marine fogs are studied. The results confirm the conclusions of the first study, demonstrating even more clearly the direct relationship of drop weight to nucleus weight. The fog drops must have grown in supersaturated air, because in almost all of them the salt concentrations were below the equilibrium values for saturated air. However, the number and sizes of the salt nuclei in the air and fog support the idea that the fogs probably developed first as moderate haze-droplet fogs in saturated air (i.e., relative humidity 100%). A temperature-mixing ratio diagram is used to explain how saturation may be sustained by mixing, for the time intervals required for these haze-drop fogs to develop.

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Michael B. Meyer, G. Garland Lala, and James E. Jiusto

The Cloud Physics Section of the Atmospheric Sciences Research Center-State University of New York at Albany conducted a cooperative field study (FOG-82) during the autumn of 1982 as part of an ongoing radiation-fog research program. A computer-controlled data-acquisition system consisting of sophisticated soil, surface, and boundary-layer sensors, as well as contemporary aerosol and droplet probes was developed. These data are being used to address a variety of critical problems related to radiation-fog evolution.

Scientists from 10 universities and research laboratories participated in portions of FOG-82. Research objectives included studies of fog mesoscale meteorology, radiation studies, low-level water budget, vertical fog structure, fog supersaturation, condensation nuclei, and fog-water chemistry, as well as radiation-fog life cycles. A comprehensive description of the FOG-82 program and objectives is presented.

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G. Garland Lala, Eric Mandel, and James E. Jiusto

Abstract

A numerical model of radiation fog was developed in order to test the sensitivity of variables comprising the model, and evaluate its capability for forecasting the onset of fog from standard radiosonde weather data. Four case studies were considered that included both fog and no-fog occurrences. The variables examined–initial surface temperature and moisture conditions, eddy exchange profiles, radiative flux divergence, and dew formation–were all found to influence critically the model's performance. Prediction of fog occurrence and temperature were reasonably encouraging provided a judicious (though somewhat arbitrary) choice of eddy mixing values was made.

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Michael B. Meyer, James E. Jiusto, and G. Garland Lala

Abstract

An extensive boundary-layer field program was conducted which included simultaneous measurements of visibility and particle size distributions during fog and haze. Several empirical expressions relating changes in visibility to characteristics of the aerosol (droplet) size spectrum and relative humidity are presented and evaluated. Detailed analysis of one evolving dense fog revealed several points of interest regarding the behavior of drop size spectra, including a scheme for approximating fog supersaturation.

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atmospheric sciences and problems of society

A series of statements on the relevance of the scientific and technological areas of AMS STAC Committees to national and international problems

Earl G. Droessler, John W. Winchester, Guy A. Franceschini, O. H. Daniel, J. Doyne Sartor, James E. Jiusto, and Thomas A. Gleeson
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