PRECI 





Figure VI-7 — CONCENTRATION OF ICE NUCLEI IN A CITY 



The diagram shows the concentration of ice nuclei observed in Seattle. Washington, 

 from 1 July to 3 November 1968. The scale gives the numbers of ice nuclei per 

 300 liters of air active at — 21 °C. The concentrations measured in the city were six 

 times greater than the concentrations of nuclei measured at two unpolluted non- 

 urban sites. From the plot of the concentrations on the wind rose, it is possible to 

 deduce that there are sources of nuclei SW and SSW of the sampling site, which 

 was in the northeastern part of the city. Analyses show that man-made sources of 

 ice nuclei dominate over natural ones. Just what effect these nuclei have on the 

 microstructure of clouds, and the development of precipitation, is not known, 

 although studies in a growing number of cities seem to show that precipitation 

 increases downwind of industrial areas. 



Less expensive and more readily avail- 

 able materials are needed. Seeding 

 materials that have beneficial side 

 effects (such as fertilizing character- 

 istics) or no side effects are desirable. 

 More precise delivery techniques are 

 needed so that the results of the treat- 

 ment can be properly targeted and 

 so that the optimum effect can be 

 achieved. 



Better specification of the extra- 

 area effects recently discovered is 



necessary for both targeting and eval- 

 uation. The causes of the extra-area 

 effects need to be understood so that 

 the recognition and treatment systems 

 can take the effects into considera- 

 tion. Inadvertent modification of 

 clouds by atmospheric pollutants is 

 another vital but little understood 

 issue. (See Figure VI-7) In some 

 situations, inadvertent modification 

 can be controlled. In others, it cannot 

 be controlled but can be considered 

 as a factor in the precipitation-aug- 



mentation system. Similarly impor- 

 tant are the interactions between two 

 or more neighboring augmentation 

 projects. 



Advanced studies of both the posi- 

 tive and negative interactions of pre- 

 cipitation augmentation with other 

 systems need to be carried out. Fac- 

 tors in the natural environment will 

 be affected by changes in precipi- 

 tation. Short- and long-term con- 

 sequences must be assessed from 

 scientific, economic, and cultural view- 

 points. The studies should not be 

 limited to just the more obvious is- 

 sues, such as ecological effects. The 

 studies should consider the entire 

 environmental system, which in- 

 cludes man. 



Increasing interest in the environ- 

 ment by both the scientific commu- 

 nity and concerned citizens' groups 

 argues for a more deliberate study of 

 the environment as a system. Much 

 literature has been circulated recently 

 suggesting our impending doom if 

 the quality of the environment con- 

 tinues to deteriorate. Other studies 

 have shown that severe water short- 

 ages will be widespread by the year 

 2000. While some of these state- 

 ments may not be rigorously based 

 on fact, they do suggest the impor- 

 tance of early development of a tech- 

 nology that can play a role in en- 

 hancing both the quality and quantity 

 of the water portion of the envi- 

 ronment. 



How rapidly the fully devel- 

 oped precipitation-augmentation sys- 

 tem described above can be made 

 available is in part a function of the 

 level of effort. The first such system 

 could be operational by 1975. This 

 system will be effective for win- 

 ter orographic storm situations in 

 sparsely populated, high-elevation 

 areas. Shortly thereafter, a similar 

 system for convective clouds could 

 be operational. Through evolutionary 

 processes, systems for other cloud 

 situations, and improved versions of 

 the first, could be available by the 

 1980's. 



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