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  • Author or Editor: JAMES E. JIUSTO x
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Edmond W. Holroyd III
and
James E. Jiusto

Abstract

Few documented cases exist to demonstrate that highly convective supercooled clouds can be completely glaciated or overseeded. By “overseeding” we imply a sufficient concentration of ice nuclei to accommodate all the water generated in the updraft and to consume rapidly the existing cloud liquid water. One such case is herein presented that describes the ground variations in snow crystal type, size and concentration as a seeded cloud passed by. During this period, snow crystal concentrations increased by approximately two orders of magnitude, and, within the limits of accuracy of the experiment, showed a one-to-one correspondence with the concentration of silver iodide released. Snowflake aggregates were dominant and individual crystals comprising the aggregates averaged only 200 μ, in general agreement with model predictions. Riming of crystals was significantly reduced, with thick plates and solid columns indicative of a “dry” environment replacing the original rimed dendrites. It was evident that heavy seeding, while limiting the riming and size of individual crystals, amplified the snowflake aggregation mechanism.

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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
,
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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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
,
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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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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