l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



explained by changes in the balance between incoming and outgoing 

 radiation. In summer the land masses in high latitudes absorb solar 

 heat and this absorption increases with increased solar radiation. 

 There is also' an increase of cloudiness at that time which should play 

 an important role in determining the effect of increased solar radia- 

 tion on the atmosphere. In autumn an increased atmospheric cir- 

 culation causes an excess of warni water and of cloudiness in the 

 North Atlantic and North Pacific with an accompanying diminution of 

 pressure. The same increase in atmospheric circulation determines an 

 increased flow of cold water along the north coast of Africa and of 

 Western Mexico and thus determines the opposite annual period in 

 these regions to that in the northern part of the same oceans. 



The seasonal shifting in the centers of maximum solar action in 

 the atmosphere are thus plausibly related to changing physical con- 

 ditions in the atmosphere and in the surface conditions of the earth. 



IV. ATMOSPHERIC WAVES 



When atmospheric changes, whether of pressure, temperature, or 

 wind movement are analyzed into oscillations of different lengths 

 they are usually found not to be stationary but to progress from 

 point to point. The short oscillations move fastest and the longer 

 oscillations progress more and more slowly with increasing length. 

 They thus have some analogy to ocean waves and are frequently 

 called waves. 



Meteorological data may be analyzed into longer and shorter oscil- 

 lations by means of smoothing, by means of using changes of suc- 

 cessively greater length, by means of sine curves derived from indi- 

 vidual periods, or by the process of averaging successive periods, 

 using trial periods of different length. These processes are described 

 and illustrations given in " World Weather." ^ 



The method adopted for the present research was to select from 

 plotted curves the cases where an oscillation of some particular 

 length was unusually strong and then to get the average of several 

 successive oscillations, so as to eliminate oscillations of longer period. 

 This process was repeated successively for each particular oscillation 

 selected, dropping one and adding another later in time. An example 

 of the method is shown in table 6 for St. Paul, Minnesota. The data 

 were obtained from the Washington 8 a. m. weather map. 



The consecutive means of four successive periods, obtained as 

 shown in table 6 for the months of November and December, 1927, 

 are plotted in figure 12 for a series of stations running from Nome, 



^ Clayton, H. H., World Weather, p. 114. New York, Macmillan & Co., 1923. 



