NO. 2 



THE SUNSPOT PERIOD CLAYTON 



The curve for Stykkisholm is an interesting type. In 1 870 and 

 again in 191 7, it shows maxima which coincide with the sunspot 

 maxima while from 1875 to : 9°9 the oscillations are the reverse of 

 the sunspot oscillations. Here then is a period whose maxima and 

 minima coincide approximately in time with those of the sunspots 

 but invert in phase from time to time. In the Bulletin of the American 

 Meteorological Society for July 1938, page 218, it was shown that 

 this inversion in phase was caused by a change in latitude of the 

 departures from normal pressure with an increase of solar activity 

 (see fig. 5). To obtain the lines of equal departure shown on these 

 charts the pressures at more tban 200 stations were smoothed in 

 the same way as those of Stykkisholm. 



However, the atmosphere does not oscillate back and forth between 

 the centers of plus and minus departures with a fixed zero line 



20 

 0.0 -1.0 



1870 1880 1890 1900 



I I I I j I I I I I I I I I J II I I I I I I I I I I I I II I II J I I I I 



1910 1920 1930 



I I I I I I U I I I I I I I I I I I I I I II I I I 



I I I I 1 I I I I I I I I I I I I I I I I I I I 1 I I I I I I I I I I I I I I I I I I I 1 I M I I I I I I 1 lYl I I I I I I 1 



Fig. 4.— Smoothed annual pressures and sunspot numbers. 



between them, as might be thought on examining the charts in figure 5, 

 but there occurs a gradual shift of the centers of excess and defect of 

 pressure. This process is illustrated by the curves in figures 6 and 7. 

 It is seen from the first series of curves in figure 6 that, at the time 

 of sunspot maximum in 191 7, a barometric maximum existed in high 

 latitudes over the North Atlantic, as shown by the pressures at Jacobs- 

 havn and at Stykkisholm. At stations farther south this maximum 

 occurred successively later, until in the latitude of Madeira the pres- 

 sure oscillated nearly inversely to that of the sunspots. The same 

 conditions apparently occurred in the North Pacific, as shown by the 

 second series of curves in figure 6. The stations are situated near the 

 Pacific Coast of North America. At Tanana the maximum of pres- 

 sure occurred nearly at the time of sunspot maximum, but came 

 successively later at lower latitudes, until at San Diego the curve is 

 nearly inverse to the sunspot curve. 



On the other hand, over low latitudes on or near the central conti- 

 nental masses of North America and Asia a minimum of pressure 



