Cumulus Studies -44- 



with dry ice or with water are essentially no different from those that occur 

 spontaneously in nature. "However," it went on, "there will frequently be 

 cases where the cloud is not yet ready or ripe for spontaneous development 

 of snow or rain, although it may be possible to produce these effects by 

 seeding." It concluded with the following significant summary: 



"When we realize that it is possible to produce self- 

 propagating rain or snow storms by artificial nucleation 

 and that similar effects can be produced spontaneously by 

 chain reactions that begin at particular but unpredictable 

 times and places, it becomes apparent that important 

 changes in the whole weather map can be brought about 

 by events which are not at present being considered by 

 meteorologists. I think we must recognize that it will 

 probably forever be impossible to forecast with any great 

 accuracy weather phenomena that may have beginnings 

 in such spontaneously generated chain reactions." 



STUDIES IN PUERTO RICO 



All these studies and tests which had been made, and theories which 

 had been evolved as a result, with regard to the nature, behavior, and modi- 

 fication of cumulus clouds were an important background to another signif- 

 icant milestone in the history of Project Cirrus. That was the expedition 

 to Puerto Rico in February, 1949. ^^' 



The objective of this trip was mainly to determine the type and physical 

 characteristics of the clouds that occur in Puerto Rico during the winter 

 months, particularly the month of February, and, if suitable clouds were en- 

 countered, to develop and possibly to evaluate water-seeding techniques. Con- 

 siderable personnel took part in the project, a supply of planes was available, 

 and a large quantity of photographs was made. 



At least two new precipitation sequences were observed, and considerable 

 data were accumulated to permit a better understanding of the processes in- 

 volved. Also studied was the trade wind inversion, a dominant feature which 

 controls cloud and precipitation development in the West Indies region during 

 February. A better understanding of this phenomenon should lead to a better 

 understanding of tropical meteorology. 



The cumulus clouds were observed to have a different character than 

 those common in the eastern United States. Contacts made with interested 

 local people in Puerto Rico were expected to lead to the accumulation of 

 some excellent supplementary data on raindrop size, convergence of winds, 

 and the observation of double orographic cloud streams from the Liquillo 

 Mountains. 



