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ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 5 



fluctuation is called positive when pressure is high in the southern 

 Pacific and low in the Indian Ocean, and temperature is mostly low 

 in the Tropics ; but the economic importance is in connection with 

 rainfall, for the fluctuation has a correlation coefficient of over 0.8 

 with the gummer rainfall of northeast Australia, over 0.7 with the 

 monsoon rainfall of India and with the Nile floods, 0.6 with the 

 rainfall of large areas in South America, and over 0.5 with that of a 

 region in South Africa. 



A surprising fact comes out on comparing the numerical series 

 giving the characteristics of the summer and winter values of this 

 fluctuation, the control of the southern winter on the succeeding 

 summer being expressed by a coefficient of 0.82, the corresponding 

 data being plotted together in figure 8; but the relationship with 

 the previous summer is only 0.2. The immediate effect of this is 



FiGDRB 8. — Forecast of December to February from previous June to August. 



that numerical values of the winter oscillation give us a means of 

 predicting 3 months in advance, at any rate approximately, the sum- 

 mer values of the oscillation and therefore of the pressure, tempera- 

 ture, and rainfall associated with them. In figure 9 are the rela- 

 tionships of the values of the pressure, temperature, and rainfall of 

 December to February, with the numbers indicating the fluctuation 

 of the previous June to August. These express relationships which 

 have held for about 50 years, and show that we have arrived, not 

 at a mathematical figment, but at a physical reality of commercial 

 value. 



These methods of prediction can be improved on by study of the 

 relationships of individual areas. For example, the coefficient of 

 0.64 of rainfall of northeast Australia with the oscillation of the 

 previous winter becomes 0.79, when we base it on previous pressure 

 at Honolulu, Port Darwin, and South America; a comparison of the 



