NO. 7 Till-: ATMOSTHERE AND THE SUN CLAYTON 29 



Laiv of longitude displacement of periodic zuavcs. — Periodic waves 

 tend to drift eastward at a rate of 180° of longitude in one period, 

 whatever the length of the periofl. The centers of greatest departure 

 are found in high latitudes, 60° to 80° from the Equator. 



There are several factors which make this drift toward the east 

 difificult to follow. First there are the factors depending on solar 

 changes descrihed in the latitude efifect and which are nearly instan- 

 taneous with solar changes. There are also seasonal factors and 

 probably others which influence the results. 



Examining the successive charts in figure 18 it is found that the 

 magnitude of the departures in the 7.5-year period decreased rap- 

 idly as the central areas passed into Siberia and increased again 

 over Kamchatka. This enhanced intensity in the departures coincided 

 with a maximum of solar activity as will be seen later. 



Another disturbing factor is the formation of centers of distur- 

 bance moving at right angles to the nonnal waves. When waves of 

 high pressure and low temperature are advancing from the north- 

 west, low pressure areas form in front of them and advance from 

 southwest to northeast. These disturbances advancing toward the 

 northeast are particularly frequent over the wann ocean waters to 

 the east of Asia and of North America. These cross currents greatly 

 complicate the nonnal movement of atmospheric waves and make 

 analysis of the data difficult. 



V. RELATION OF THE WEATHER WAVES TO SOLAR CHANGES 



If the values of solar radiation observed by the Smithsonian 

 Astrophysical Observatory simultaneously with the pressure waves 

 are treated in the manner just described they show in each case 

 wavelike changes of the same length as the pressure waves. 



Figure 19 shows the successive means of four periods of seven 

 days in solar radiation during Noveml>er and December, 1927, com- 

 pared with the atmospheric pressure observed at the same time at 

 Eagle, Alaska, and treated in the same manner as in table 6. The 

 dotted curves in each case show the harmonic values of the 7-day 

 wave computed from the data. Compare this diagram with the plots 

 in figure 12. 



Figure 20 shows the means of successive values of a period of 13.6 

 days in solar radiation and in pressure derived from the means of 

 two periods. This diagram may be compared with the plots in fig- 

 ure 13. The dotted curves in figure 20 show harmonic curves com- 

 puted from the data. 



