erational, where this type of fog is prevalent, with a return in benefits 

 six times the cost of the program. Warm fog is even more prevalent, and 

 it seems likely that a similar benfit-to-cost ratio will be attained when the 

 operational techniques for its dispersal are perfected. 



It is estimated that the hurricane modification program alone, when 

 operational, would cost about $5 million annually and could reduce prop- 

 erty damage and related costs by $100 million annually, a benefit- to-cost 

 ratio of 20 to 1 . 



There is another vast area which suffers a shortage of annual precipita- 

 tion, reaching drought proportions in far too many years. This is the 

 northern Great Plains area of the country. In this region, where summer 

 rainfall is both scanty and sporadic, crop-production technique is based 

 on trapping a portion of 1 year's rainfall to help support grain production 

 in the subsequent year, and one crop is produced each 2 years per unit 

 of land area. On the basis of soil quality, the potential exists for annual 

 crops given a modest increase in rainfall. This area, which has been 

 largely ignored by the Federal Government in its weather modification 

 program, should be explored. 



TECHNICAL OBSTACLES TO PROGRESS 



Progress in any technical endeavor depends upon our theoretical under- 

 standing, our ability to measure, our facilities for experimentation, and 

 our ability to mount and manage large-scale field experiments. We have 

 made significant progress in all four areas in the last decade. 



Understanding 



In order to make progress in the National Projects and other applica- 

 tions of weather modification, a great deal more must be learned about 

 the natural weather processes and how these processes can be modified to 

 bring about the desired effect. Some of these areas where measurements 

 are essential include: 



• origin, detection, and counting of natural ice nuclei; 



• modes of nucleation, optimum particle size and numbers, and inad- 

 vertent sources of artificial ice nuclei; 



• detection, counting, and variability of natural cloud condensation 

 nuclei ; 



• inadvertent sources of artificial cloud condensation nuclei; 



• water vapor, liquid water, rate of riming, cloud drop size, etc.; 



• ice crystal type and size; and 



• temperature in cloud, vertical and horizontal flow, electrical field, etc. 



Instrumentation 



The key to increasing our knowledge of the processes involved is ac- 

 curate measurements of all of the needed information. This requires de- 



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