NO. 6 



SOLAR RADIATION AND WEATHER CLAYTON 



37 



It is thus made evident that within the tropics the pressure falls 

 with increased solar radiation and increases with decreased radiation, 

 while in high latitudes the centers of high and low pressure swing 

 north and south both in winter and in summer in unison with the 

 variations of solar radiation, but there is a seasonal change in the 

 positions of the centers of high and low over the continents and 

 oceans. This latter fact is brought out clearly by comparing the dis- 

 tribution of excess and deficiency of pressure with high solar radia- 

 tion in July, 1917 (shown in fig. 28), with the distribution found with 



Solar radiation two percent below normal — July 1910. 



Fig. 31- 



high, solar radiation in January, 1920 (shown in fig. 20). In both 

 cases there is a defect of pressure in equatorial regions while in high 

 latitudes there is an excess of pressure over the continents in winter 

 with a defect in summer, and the reverse sequence over the oceans. 



The polar anticyclone, or area of high pressure, appears also to 

 expand and contract with variations in solar energy, being smallest 

 when the radiation is high, but more observations are needed within 

 the polar circle to make this certain.^ 



If, owing to the difficulties in measuring solar radiation, the given 

 variations from the mean are too large, so that 2 per cent, let us say, 

 should be i per cent, then the results are even more impressive of the 

 power of solar changes to produce changes in our atmosphere. 



^ For further evidence see World Weather, pp. 264-265. 



