NO. 7 THE ATMOSPHERE AND THE SUN CLAYTON 2/ 



A proportional rate of progress appears to occur in the periodic 

 wave of about 7.5 years. Figure 17 shows the centers of oscillation in 

 a 7.5-year wave on a world map. This map is derived from har- 

 monic values computed from groups of three periods between 1883 

 and 1913 at 117 stations scattered over the world. It shows the 

 centers of oscillations at the epochs, 1885, 1893, 1900, etc. Con- 

 tinuous lines show equal values above normal and broken lines show 

 equal values below normal. It is not possible with available data 

 to follow the progressive movement of all the centers, but the center 

 over Greenland shows a distinct progress from west to east. This 

 progress will be evident from figure 18 which shows the centers of 

 oscillation in the area between 50° W. and 120° E. north of the Equa- 

 tor when the epochs are taken successively two years later. The 

 results in figure 18 are derived from the data of 48 stations taken 

 from " World Weather Records." 



In 1885 there was a marked excess of pressure over Greenland 

 (see fig. 17) ; in 1887 this center of excess pressure is displaced to 

 Norway ; in 1889 this center is over the northern part of central 

 Siberia; two years later, in 1891, it is over the northern part of 

 western Siberia. The progress of the centers is shown by small cir- 

 cles in the upper chart of figure 18. The circles show that the center 

 was displaced eastward about 180° in a period of 7.5 years or at a 

 rate which would cari-y it around the world in two oscillations of 

 this period. 



In his study of the 2^-year period Mr. Clough ^ found that the 

 epochs at Portland, Oregon, preceded those at Toronto by about 

 0.75 year. The difi^erence in longitude is 43°. At that rate the epoch 

 would move about 150° of longitude in one period, or approximately 

 around the world in two periods. 



The charts given by Dr. Weickmann in his study of the 24-day 

 period referred to previously do- not show the drift in longitude so 

 clearly as the drift in latitude. However, in his charts there are 

 found centers of maximum departure which show a drift in longi- 

 tude. A center in the Aleutian Islands on December 10, 1923, moved 

 eastward across Canada to Labrador in 1 1 days, which is at the rate 

 of about one period for 180° of longitude ; but a center near Green- 

 land moved eastward to northern Siberia and then retreated. 



The longitude drift of the waves is, hence, not so clearly defined 

 as the latitude drift ; but there is undoubtedly a trend which may be 

 stated as follows : 



^ Monthly Weather Review, Vol. 52, No. i, p. 39, Jan., 1924. 



