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<br />crystals and the' amount of cloud water which reaches the ground. If <br /> <br />seeding is heavy enough, the predominate crystal type should be modified. <br /> <br />The reduction in accretional growth should produce less heavily-rimed <br /> <br />crystals and, if diffusional growth is affected, less dendritic forms <br /> <br />but more plate forms should appear. There could also be the appearance <br /> <br />of solid prisms rather than hollow prisms if the temperature is appropriate. <br /> <br />The heavier the seeding the greater should be the effects on the character- <br /> <br />istics of the precipitating ice crystals. If excessive concentrations <br /> <br />of artificial ice nuclei are added to orographic clouds, many ice crystals <br /> <br />remain too small' to fallout and therefore sublimate downwind. This <br /> <br />would have the effect of actually decreasing the amount of precipitation <br /> <br />I <br />which would have! occurred naturally. <br /> <br />One significant complication in this investigation of ice crystals, even <br /> <br />under ideal orographic cloud precipitation conditions, is the change in <br /> <br />ice crystal trajectories due to flow regimes and growth rates for different <br /> <br />storms. This is particularly true when comparing seeded versus natural <br /> <br />, <br />precipitation even for identical storms. The ice crystal trajectories in <br /> <br />seeded storms are longer because of smaller crystal sizes and consequently <br /> <br />the ice crystals have lower fall velocities, which cause the precipitation <br /> <br />to occur further downwind. <br /> <br />-5- <br />