SEASONAL WEATHER PREDICTION — WALKER 135 



thought will make it clear that a man will in the long run be right 

 three times out of four if, when last year's rain was in defect, he 

 predicts an increase, or if it was in excess he forecasts a diminution. 

 So I think it is not unfair to say that success under the Swedish 

 conditions begins at 75 percent. The success actually attained is 82 

 percent, which is encouraging; and the success in dealing with water 

 levels is phenomenally great, being slightly over 90 percent. 



The seasonal conditions of Russia, which are not very closely 

 related with those of the North Atlantic, have been carefully 

 examined by W. Wiese. In 1923 the Hydrometeorological Office 

 of Leningrad started publishing forecasts of ice in the Barents Sea, 

 and out of 17 monthly forecasts of which I have information 15 were 

 approximately correct. Predictions of the rainfall of April and 

 May in central and east Russia were initiated at the same time, and 

 all the first 4 years they were approximately correct; the biggest 

 difference between the actual and forecasted amounts was only 

 20 percent. 



No account of European activity in this department could ignore 

 the enterprise of Prussia 4 years ago in creating at Frankfort a. M. 

 a post for research into long-period forecasting. Dr. Franz Baur 

 has for the present wisely limited his activity to the issue of a fore- 

 cast of 10 days ; it would be impossible to expect results under these 

 conditions which are as accurate as those of daily weather work, but 

 I am informed that their standard fully demonstrates the trust- 

 worthiness of the principles employed. It is only by experiments of 

 this kind that satisfactory methods of prediction can be developed. 

 We may now pass to the consideration of improvements in our 

 methods, and the fundamental question at once arises — what is the 

 physical cause of seasonal fluctuations? We should naturally look 

 for it in variations in the energy received from the sun, and it is 

 surprising that an increase in solar activity as measured by sun spots 

 produces a slight decrease in the circulations in the North Atlantic 

 and the North Pacific. In the southern fluctuation the tendency of 

 numerous spots is to produce positive valuas, but even there the 

 biggest seasonal correlation coefficient is only 0.26, which is much 

 too small to provide the explanation that we seek. Moreover, it 

 probably arises because a positive fluctuation is associated with 

 low temperatures between latitudes 40° N. and 40° S., and these are 

 linked with an increase in sun spots. 



In order to verify that the daily pressures are not produced by 

 short-lived emanations from the sun tabulations of the relationships 

 between daily and weekly, as well as the monthly and seasonal, values 

 at distant places have been made; for if the daily values over the 



