Weather Mod Critical Issues Report

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- I I I I I I I I I I I, I I I , I I I I I modification of clouds. We concur with the need to improve and refine models of cloud processes, but existing models can be used as a first step to examine, for example, the possible physical responses to hygroscopic seeding that occur several hours following the cessation of seeding. In addition, existing models can be used to replicate the transport and dispersion of ground-based and aircraft-released seeding agents and the cloud and precipitation responses to those seeding materials in winter orographic clouds. Existing models can also simulate static and dynamic seeding concepts for fields of supercooled convective clouds, Moreover, existing models can be used to improve the efficiency of the operation of weather modification research projects and operational programs, and be deployed in the assessment of those programs. . We recommend that a wide range of cloud and mesoscale models be applied in weather modification research and operations. This includes various microphysics techniques (both bin and bulk-microphysical models have their uses) and various approaches in the dynamics (all dimensionalities - one, two, and three dimensional models - offer applications). The application of hybrid microphysical models should be especially useful in simulating hailstorms and examining various hypotheses and strategies for hail suppression, . We recommend that a concerted effort be made in the field and through numerical modeling, which includes simulations of hailstone spectra, to study hailstorms and the evolution of damaging hailstones as well as examine potential impacts of modified hailstone spectra on the severity of storms. Because operational programs regarding hailstorms are currently being conducted in the U. S., we encourage the "piggybacking" of research on such projects. We also encourage active cooperation with international hailstorm projects to elicit data and information concerning suppression concepts and technology. . We recommend that an instrumented armored-aircraft capability (storm penetration aircraft, or SPA) be maintained in the cloud physics and weather modification community. This is essential for the in situ measurements of severe storm characteristics and for providing a platform for some of the new instruments described in the NRC report. . We recommend that support be given for the development of innovative ways to evaluate operational cloud seeding projects. This is particularly important for the establishment of the physical basis of various cloud seeding methods and for establishing the possible range of cloud seeding effects. . We recommend that evaluation techniques presently being applied to operational programs be independently reviewed, and as necessary revised to reduce biases and increase statistical robustness to the extent possible. Recognizing that randomization is not considered to be a viable option for most operational seeding programs, we acknowledge that there is much room for improvement in most present evaluations, many of which are presently done in-house, 5