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A two-dimensional time-dependent cloud model which covers a region 19.2 km × 19.2 km in the x and z directions with 200 m grid intervals, has been used to simulate silver iodide (AgI) seeding effects on strong convective clouds. The model is a set of conservation equations for momentum, energy and mass (air and water contents). One extra conservation equation is applied to trace the seeding agent which advects and diffuses along the flow field and interacts with the supercooled cloud fields. Contact and deposition nucleation are simulated. Only inertial impact and Brownian collection are considered as possible mechanisms for contact nucleation. Most of the AgI particles work as deposition or sorption nuclei in this study. Three different soundings are tested. Most of the effort is used in testing sounding H1, from Miles City, Montana, 29 July 1975. Seeding at a different place (see H1/P1), at a different time (case H1/T1), and with different amounts of AgI (cases H1/M1 and H1/M2) are simulated. The effects of natural ice nuclei are also tested (cases H1/N2, H1/N3 and H1/S3). The model results show a “time window” for the icing process in natural (unseeded) cases. This time window is related to the concentration of the natural ice nuclei and the flow pattern. Concerning seeding effects, this study shows the potential to augment precipitation by AgI seeding. This potential is closely related to the dispersion of the proper amount of seeding agent into the proper region and at the proper time to obtain optimum effects.
Hsie et al. (Fri,) studied this question.