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A STUDY OF THE RADIATION OF THE ATMOSPHERE 



BASED UPON OBSERVATIONS OF THE NOCTURNAL RADIA- 

 TION DURING EXPEDITIONS TO ALGERIA 

 AND TO CALIFORNIA 



By ANDERS ANGSTROM 



SUMMARY 

 The main results and conclusions that will be found in this paper 

 are the following-. They relate to the radiation emitted by the atmos- 

 phere to a radiating surface at a lower altitude, and to the loss of 

 heat of a surface by radiation toward space and toward the atmos- 

 phere at higher altitudes. 



I. The variations of the total temperature radiation of the atmos- 

 phere are at low altitudes (less than 4,500 m.) principally 

 caused by variations in temperature and humidity. 

 II. The total radiation received from the atmosphere is very nearly 

 proportional to the fourth power of the temperature at 

 the place of observation. 



III. The radiation is dependent on the humidity in such a way that 



an increase in the water- vapor content of the atmosphere 

 will increase its radiation. The dependence of the radi- 

 ation on the water content has been expressed by an 

 exponential law. 



IV. An increase in the water-vapor pressure will cause a decrease 



in the effective radiation from the earth to every point of 

 the sky. The fractional decrease is much larger for large 

 zenith angles than for small ones. 

 V. The total radiation which would be received from a perfectly 



dry atmosphere would be about 0.28 — 5 — r with a 



J L cm. mm. 



temperature of 20°C. at the place of observation. 

 VI. The radiation of the upper, dry. atmosphere would be about 

 50 per cent of that of a black body at the temperature of 

 the place of observation. 



Smithsonian Miscellaneous Collections, Vol. 65, No. 3. 



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