THE INTENSITY OF SOLAR RADIATION AS RECEIVED AT THE 

 SURFACE OF THE EARTH AND ITS VARIATIONS WITH LATITUDE, 

 ALTITUDE, THE SEASON OF THE YEAR AND THE TIME OF DAY 



Herbert H. Kimball 



Blue Hill Meteorological Observatory of Harvard University 



AND Irving F. Hand 



U . S. Weather Bureau 



Introduction. Measurements of solar-radiation intensity at normal incidence. 

 The vertical component of the total solar radiation {direct + diffuse) received at the surface 

 of the earth: Solar-radiation intensities in tropical, subtropical, and Arctic regions — The 

 effects of cloudiness on the total solar radiation received on a horizontal surface. Summary. 

 References. 



INTRODUCTION 



This paper treats of the intensity of solar radiation as received at the 

 surface of the earth. The subject is divided naturally into two main 

 topics, as follows: (a) The intensity of direct solar radiation as received 

 on a surface normal to the incident solar rays; (6) the intensity of the 

 total solar radiation (direct + diffuse) as received upon a horizontal 

 surface. 



The Standard of Pyrheliometry . — In the United States, the pyrhelio- 

 metric standard has been the Smithsonian Standard of Pyrheliometry 

 of 1913 (1). In Europe the Angstrom compensation pyrheliometer (5) 

 is extensively used as a standard. The ratio, Smithsonian standard/ 

 Angstrom standard = 1.035, has been employed at some European 

 observatories, notably at the observatory at Davos, Switzerland (6), 



o 



to reduce measurements by the Angstrom pyrheliometer to the Smith- 

 sonian scale. It is necessary, therefore, in comparing pyrheliometric 

 measurements made in different countries, to have in mind this difference 

 in standards. Recently the Smithsonian Institution revised its stand- 

 ardization tests, and announces that its standard pyrheliometry of 1913 

 is about 2.3 per cent high (2). On account of the long series of measure- 

 ments and deductions therefrom already published, it was considered 

 less confusing to adhere to the 1913 scale of pyrheliometry, but to make 

 clear the amount by which it is in error. The U. S. Weather Bureau has 



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