NO. 15 WEATHER AND SOLAR ACTIVITY CLAYTON I7 



vol. 90. The computed correlation coefficients and the amount of 

 change in pressure for each change of i per cent in solar radiation 

 are given in table 3 on page 36. The data all relate to the 10 years 

 1921-1930. 



The correlation coefficients are plotted on maps, one for the whole 

 period of 120 months in figure 15, and others for the seasons sep- 

 arately in figures 16, 17, 18. and 19. The correlations for the entire 

 period of 120 months are not large, but the charted results show 

 that minus correlations prevail over the Indian Ocean, equatorial 

 Africa, the equatorial Atlantic, and along the Gulf Stream up to 

 Iceland. The minus correlation signifies that with increased solar 

 radiation the pressure falls within those areas where the pressure 

 is normally low, and the plus correlation shows that it tends to rise 

 within belts between 20° and 40° both north and south of the Equator. 

 In other words, with increased solar radiation the normal areas of 

 high and low pressure in the atmosphere are accentuated and the 

 normal atmospheric circulation speeded up. 



It is also to be noted that there are well-defined centers of plus and 

 minus correlation. The center of plus correlation over Siberia may be 

 called the Gobi Desert center ; the one over northern Africa and the 

 adjacent Atlantic, the Sahara center; the one over the Pacific west 

 of lower California, the Pacific center; and the one over Labrador, 

 the Labrador-Greenland center. It is significant that the areas of 

 minus correlation, as pointed out in the case of sun-spot maxima, are 

 in regions where the water temperatures and vapor pressures are 

 high, and the centers of plus correlations are in regions where the 

 vapor pressures are low. This fact suggests very strongly, if it does 

 not prove, that the fall of pressure with increased solar radiation is 

 due to the absorption of the increased radiation by the water vapor 

 in the air, the heating of the air, a consequent lowering of the pres- 

 sure, and an overflow of air to the colder and drier regions of the 

 earth. 



With the four seasonal charts the maximum correlation coefficients 

 are large. Figures 16 to 19 show that although the areas of minus 

 correlation vary in area and position with the seasons, the centers of 

 greatest minus correlation are always found in regions of high vapor 

 pressure. It is of especial significance that in June to August, when 

 the sun is north of the Equator and the highest vapor pressures are 

 also north of the Equator, the greatest minus correlations are found 

 between the Gold Coast of Africa and the mouth of the Amazon 

 River in South America ; whereas in December to February, when 

 the sun is in the Southern Hemisphere and the highest vapor pressures 



