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James E. Jiusto

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James E. Jiusto

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John Zamurs and James E. Jiusto

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This work reports the results from a five-station (remote to highly urbanized) sampling network operated in 1976 in eastern New York State in which daily measurements were made of ice nucleus and condensation nucleus concentrations among the stations at most of the test relative humidities. Generally, semi-urban Albany had the highest concentration of ice nuclei and remote Whiteface Mountain the lowest. Albany also typically had the highest slope values (ice nucleus concentration-supersaturation spectrum) and the highest concentrations of condensation nuclei, while Whiteface Mountain typically had the lowest values for these two parameters. Lower ice nucleus concentrations in the New York City area suggest that the degree of urbanization there did not have a major impact on ice nucleus concentrations.

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James E. Jiusto and George E. Bosworth

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James E. Jiusto and Ronald L. Lavoie
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Patricia A. Jones and James E. Jiusto

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From historical weather records, a preliminary assessment was made of local climate changes in four major urban areas of New York State. Particular emphasis was placed on cold season precipitation and possible relationships to man's activities. Total snowfall was found to have increased significantly from about 1940, the start of a period of sharp increases in urbanization and industrialization. The relationship was merely coincidental, with the underlying cause of snowfall increases due to natural causes, apparently in part to a corresponding decline in ambient temperature. A few climate trends appeared linked to anthropogenic causes, particularly in New York City.

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G. Garland Lala and James E. Jiusto

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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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Edmond W. Holroyd III and James E. Jiusto

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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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James E. Jiusto and G. Garland Lala

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Roland J. Pilié and James E. Jiusto

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Contrails were produced for laboratory study by burning aircraft fuels under controlled conditions of ambient temperature and humidity at pressure altitudes between 1000 and 300 mb. Observed critical formation temperatures differ from Appleman's theoretical data in a manner similar to that obtained on project CLOUD TRAIL flights. Laboratory experiments with these trails proved that the initial phase of the condensed moisture is liquid and produced strong evidence that, contrary to general belief, the final phase is sometimes liquid. Additional evidence was obtained indicating that Appleman's criterion for a barely visible trail (0.004 g per m3 of condensed moisture) is very nearly correct for ideal conditions of observation such as used in the laboratory, but is probably small by an order of magnitude or more for adverse conditions. By modifying Appleman's theory to allow for the production of a visible quantity of liquid water under adverse viewing conditions, agreement is reached with project CLOUD TRAIL data. Also presented is a simple interpretation of the theory which substantially reduces the labor required to compute critical temperatures for contrail formation.

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