Estimation of the Effective AgI Ice Nuclei by Two Methods Compared with Measured Ice Particle Concentrations in Seeded Orographic Cloud

Arlin B Super

Abstract


The Utah/NOAA Atmospheric Modification Program conducted a field program during early 1991, with additional support from the Bureau of Reclamation. Several aircraft missions were flown over central Utah’s Wasatch Plateau to monitor plumes of Agl (silver iodide} and tracer gas, and microphysical changes caused by the Agl seeding. This paper discusses one mission during which high-altitude, ground-based Agl release resulted in obvious enhancements in ice particle concentration. Fast-response observations of co-released tracer gas, presumably collocated with the Agl plumes, were used to define seeded zones and crosswind control zones. Two methods were used to estimate concentrations of Agl ice nuclei effective at cloud temperatures sampled by the aircraft. One method used tracer gas concentration measurements while the other was based on acoustical ice nucleus counter observations. Both methods were partially based on a cloud simulation laboratory calibration of the Agl generator done over two decades ago. The methods were compared with the ice particle concentrations apparently caused by the Agl seeding.Both approaches were found to provide a reasonable first approximation or the particular AgI aerosol produced and the sampled cloud conditions. However, caution should be exercised in applying the estimation approaches to other cloud conditions and Agl aerosols.

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