WEATHER AND GLACIATION — REEDS 301 



SOLAR RADIATION AND THE WEATHKR 



Since 1915 H. H. Clayton, retired, formerly chief forecaster for 

 Argentina, has been \mnrr the averajxes of jrroiips of hifrli, medium, 

 and low solar radiation valuos of the Astrophysical Observatory of 

 the Smithsonian Institution in attempting to correlate them with at- 

 mospheric changes on the earth. He has compared these means with 

 the means of temj^eratnre and pressure variations scattered over the 

 earth and attained results wliich show sj'stematic changes which 

 seem difficult to explain on any other grounds than a real relation. 



The more usual solar find nations are irregular and occup}' a few 

 days or weeks. Clayton (1923) obtained the best comparisons of 

 day-to-day fluctuations by averaging the values of each phenomenon 

 in groups of 5, 10, or more days, after allowing, in some instances, an 

 interval of 3 days for a lag in the efTect. He noted a tendency to 

 short-period variations in 3.5, 7, and 13.5 daj's, which he attributed 

 to successive outbreaks of faculae on the solar surface. Traces of 

 similar tendencies in the weather were also observed. 



Cla'vton also noted solar radiation values of similar kind at inter- 

 vals of about 11 and 16 days, which he correlated with the movement 

 of heated gases from one side of the sun to the other. These heated 

 gases are associated with solar faculae. He observed similar varia- 

 tions in temperature at Buenos Aires in 1921. 



In addition to the day-to-day variations, Clayton has averaged 

 those for monthly, yearly, and longer periods and established an 

 intimate relation between them and those of the weather. He ob- 

 serves that the complexity of the weather changes arise from com- 

 plexities of solar radiation in Mhich changes of short period are 

 mixed with progressively longer waves of change going up into years 

 and centuries. 



Clavlon has shown that with an increase of solar radiation the tem- 

 perature rises and the pressure falls in equatorial regions and is 

 immediately followed by a rise of pressure and a fall of temperatures 

 in temperate regions, reaching a maximum between latitudes 40° and 

 G0° north and south. Over the oceans, in still higlier latitudes, G0° 

 to 70°, the relation is again direct, as in the tropics — that is, the tem- 

 perature rises and the pressure falls with increase in solar radiation. 

 From the region of maximum rise of pressure, a wave of returning 

 pressure starts toward the Equator with a velocity inversely pro- 

 portional to the length of the solar cycle and drifts eastward with 

 the eastward drift of tlie atmosphere, dying out in low latitudes. 

 This effect is true, whether the increase in solar radiation be for 

 a few days, for months, for years, or for longer periods. With the 

 solar radiation below normal, the effects for the different regions for 

 the same time of year are the reverse of those when there is an equiv- 

 alent excess of solar radiation. 



