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Robert I. Sax, Dennis M. Garvey, and Farn P. Parungo

Abstract

Isothermal cold chamber tests indicate that the NEI TB-1 pyrotechnic used in FACE after July 1975 emits a silver iodide smoke which has a much greater nucleating effectiveness in the temperature range −6 to −12°C than that emitted from the Olin pyrotechnic in predominant use in FACE prior to August 1975. The NEI TB-1 pyrotechnic was also found at “warm” temperatures to have a higher nucleating effectiveness than the U. S. Navy WMU-9 flare which also contains the TB-1 formulation. From transmission electron microscopic analyses, the size distributions of the particles produced from all three types of flares were found to be similar. Because of the small sizes of the particles (mean diameter ∼0.03 μm) a diffusive contact mechanism probably is playing an important role in the nucleation of water droplets. It is postulated that soluble potassium iodide, present in a complexed form, is detrimental at warm temperatures to the nucleating effectiveness of particles produced from the Olin pyrotechnic. Differences in nucleating effectiveness in the two TB-1 mixtures are attributed to the presence of small amounts of chlorine in the binding material of the NEI pyrotechnic.

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William L. Woodley, John A. Flueck, Ronald Biondini, Robert I. Sax, Joanne Simpson, and Abe Gagin

The Florida Area Cumulus Experiment (FACE) is a long-term program to determine the potential of dynamic seeding for increasing convective rainfall over a fixed target area. The first phase of FACE (FACE-1) provided strong indications for increased, seeding induced rainfall. The second phase, FACE-2 (beginning in June 1978 and ending in August 1980), was conducted in an attempt to confirm these indications of a positive seeding effect. The criteria for confirmation in FACE-2 were published in a NOAA Technical Report prior to program commencement. A clarification and sharpening of these confirmatory criteria are discussed in this paper. In addition, a minority position of what is to constitute confirmation in FACE-2 involving the use of linear predictor models also is discussed. This paper was written and accepted for publication before the treatment decisions of FACE-2 were known.

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