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PAUL A. ALLEE

Abstract

A continuous 15-mo. morning and afternoon Aitken nuclei concentration measurement was made during 1964–1965 at Washington, D.C. The climatological means and extreme values of the Aitken nuclei concentration were obtained and are presented in graphical form. A mean monthly stability index to measure the local stability of the atmosphere is developed and compared to the mean monthly values of the Aitken nuclei concentration.

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Ross Gunn and Paul A. Allee
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Farn P. Parungo and Paul A. Allee

Abstract

No abstract available.

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Paul A. Allee and B. B. Phillips

Abstract

Measurements have been made of the radii and free electric charges of cloud particles in supercooled cumuliform-type clouds which occurred at a 6580-ft MSL mountain observatory. Simultaneously, the positive and negative conductivities in the cloud and the atmospheric electric field at the site were recorded. The observed droplet charge distribution is symmetric about zero charge and approaches the equilibrium distribution described by the theory of random ionic diffusion electrification of cloud particles.

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Farn P. Parungo and Paul A. Allee

Abstract

To investigate the possibility of inadvertent weather modification from rocket effluent, aerosol samples were collected from an instrumented aircraft subsequent to the Voyager I and II launches. The aerosol's morphology, concentration and size distribution were examined with an electron microscope. The elemental compositions of individual particles were analyzed with an x-ray energy spectrometer. Ice nucleus concentration was measured with a subfreezing thermal diffusion chamber. The particles' physical and chemical properties were related to their ice nucleation activity. A laboratory experiment on rocket propellant exhaust was conducted under controlled conditions. Both laboratory and field experimental results indicated that rocket propellant exhaust can produce active ice nuclei. Their consequences for potential inadvertant weather modification demand additional study.

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Charles C. Van Valin and Paul A. Allee

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No abstract available.

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Griffith M. Morgan Jr. and Paul A. Allee

Abstract

Potential ice nuclei, particles which become ice nuclei when properly treated, are produced in automotive exhaust. They are activated by iodine vapor and are believed to be lead particles originating from the tetraethyl lead mixed with the fuel. The sensitivity of nucleation measurements provides an excellent method of counting submicron lead particles and monitoring the automotive component of air pollution. Measurements reported here show that the production of potential ice nuclei by a gasoline engine is at least 2 × 107 per gram Pb at −10C, 1 × 1010 per gram Pb at −15C and 1 × 1012 per gram Pb at −20C.

Some simple calculations are presented, showing that large enough numbers of potential ice nuclei are produced by the routine burning of gasoline to be useful in cloud and weather modification research. In particular, a DC-6 aircraft burning 6 gal min−1 of gasoline should produce at least 4 × 1011 nuclei sec−1 at −20C.

It is demonstrated that ethylene diiodide can be added to the gasoline supply of an automobile and that the automobile will then act as an inexpensive source of large numbers of ice nuclei.

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Hermann E. Gerber, Paul A. Allee, Ulprich Katz, Charles I. Davis, and Lewis O. Grant

Abstract

The Goetz Aerosol Spectrometer, generally considered to possess only a fair ability in resolving size distributions of polydispersed aerosols, operates properly following a modification to the geometry of the entrance to the instrument's deposition channels. Its accuracy is demonstrated with an electron microscopic evaluation of a collecting surface deposit of a thermally produced polydispersed AgI aerosol with particle sizes ranging from 60 to 1000Å In diameter.

Thus calibrated, the instrument was utilized to investigate the activity of the same aerosol as freezing nuclei. The AgI particles on the hydrophobic chrome-plated collecting foil were nucleated by sorption at water saturation for temperatures of −15 and −20C. The results appear to reflect the influence of the Kelvin effect since the activity decreased at a faster rate than predicted by the “surface area rare” and since it showed a sharp cutoff corresponding to Fletcher's theoretical size temperature predictions for ideal sublimation nuclei.

Also, field measurements were conducted on 12,000-ft Chalk Mountain (Climax, Colo.) for the purpose of measuring the sizes of active AgI-NaI nuclei emanating from acetone ground generators located at least 6 mi upwind. The size distribution of the nuclei on seeding days proved similar to what might he expected from this generator type. On non-seeding days, the number of active nuclei decreased sharply while the peak of the size distributions shifted to larger sizes.

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