NO. 15 WEATHER AND SOLAR ACTIVITY CLAYTON I3 



the center over northern Siberia has moved to a lower latitude. The 

 center of decreased pressure over the North Atlantic has moved about 

 10° of latitude toward the Equator, and the decreased pressure over 

 the North Pacific extends southeastward over the United States. Still 

 referring to figure lo. with an even lower solar activity in 1904-8 the 

 centers of excess pressure have moved southward to central North 

 America and to Southern Siberia, respectively, and the centers ofif 

 Lower California and northern Africa have increased in intensity; 

 but the pressure continues low over the equatorial belt between the 

 East Indies and northern South America. The centers of excess pres- 

 sure in southern latitudes have been displaced to latitudes between 

 30° and 40° S., and areas of deficient pressure have appeared in lati- 

 tudes between 60° and 70° in both hemispheres. 



In figure 11 the departures of the 5-year means of pressure during 

 epochs of minimum sun spots are arranged in reverse order to those 

 shown in figure 10 for maxima of six)ts. During the period of very 

 low sun-spot numbers in 191 0-14 the distribution of the areas of 

 excess and defect of pressure is almost the reverse of the distribution 

 during the period of high solar activity in 191 5-19. During the less 

 marked solar minima of 1899- 1903 and 1887-91 the reversal is less 

 evident, but it should be noted that in each case there was an excess 

 of pressure along the equatorial belt between the East Indies and 

 South America. 



CORRELATIONS BETWEEN VARIATIONS IN SOLAR RADIATION 

 AND WEATHER 



The dotted curve in figure 7 shows the annual mean values of the 

 solar constant of radiation as measured by the Smithsonian astro- 

 physical observatories. These data are plotted inverted — that is, with 

 the higher values downward, as was the case with the sun spots. The 

 curve formed in this way resembles the mean pressure curve for the 

 two selected tropical stations much more nearly than does the sun-spot 

 curve. The very low pressures in 1916-17 corresjX)nd with high values 

 of solar radiation, and the high mean values of pressure in 1922-23 

 correspond with low values of solar radiation. It should be noted also 

 that during the sun-spot period 1917-28 there were four maxima of 

 solar radiation just as there were of pressure, although the extremes 

 do not coincide exactly in time. From this we may infer that the 

 pressure changes are caused by changes in solar radiation and follow 

 changes in sun-s^wt numbers only in a general way. 



