NO. 6 SOLAR RADIATION AND WEATHER CLAYTON 3I 



the Rockv ?\Iountains and Pacific Coast, If observations had been 

 available from the extreme north, an area of marked excess would 

 probably have been found in the Arctic region north of Alaska and 

 Canada. As the intensity of solar radiation stepped downward in 

 February, the area of greatest cold (see fig. 23) moved southward 

 to the South Atlantic coast, and an area of warmth appeared in 

 northwestern Canada. With a further decreased solar radiation in 

 January, 1919 (see fig. 25), the area of warmth is found in southern 

 Canada and the northern United States, and the area of cold is found 

 in Mexico and the West Indies. With a further decrease in solar 

 energy in January, 1923, the area of greatest warmth (see fig. 27) 

 has moved southward to the southern central United States and the 

 area of cold to latitude about 10° N. to 20° N., near northern South 

 America, while a new area of cold appears in Canada and the north- 

 eastern United States. 



The areas of excessive rainfall are found within the areas of 

 defective pressure, with the area of greatest warmth to the south 

 or east, and the area of greatest cold to the north or west. Areas of 

 deficient rainfa'l are found within the areas of excess pressure, with 

 the areas of warmth to the north or west, and cold on the south or 

 east. But rainfall is much influenced by topography and that has 

 to be studied in connection with winds and the distribution of pres- 

 sure and temperature. 



In July the observations extend over a much longer interval than 

 in January, the observations running back to the year 1905, and it 

 was possible to collect data from a large part of the world from the 

 published reports of the various weather services, and from the 

 Rescau Mondial. Recent data are missing from Siberia, and obser- 

 vations are scarce over the great oceans, but it is possible by means 

 of the reports from scattered islands like Hawaii, Bermuda, the 

 Azores, the Madeiras, Guam, Fanning, Christmas, St. Helena, South 

 Georgia, South Orkneys, etc., to outline the distribution of pressure 

 over a large part of the oceans. The following months were selected 

 for study, arranged in the order of decreasing intensity of solar 

 radiation : 



Table 10 



Deviations 

 Mean solar from normal 



Month radiation in per cent 



July 1917 1.989 +2.3 



July 1905 1.972 -1-1.4 



July 1913 1 .928 —0.9 



July 1910 1. 911 — 1.8 



