S15= 
sky is 
O/0, = 1 = O71 C, 
where C is the proportion of the sky covered by clouds.t 
Of the solar radiation reaching the sea surface most is absorbed 
in the water, but a small part is reflected at the surface or Scat- 
tered back after entering the water. The vrosortion so lost, or 
albedo of the sea surface, depends on the altitude of the sun, on 
Eee cloudiness, and on the roughness of the surface. In clear 
weather the albedo increases with decreasing altitude of the sun. 
A rough surface increases the albedo slightly when the sun is in the 
zenith and decreases it considerably when the sun's altitude is low. 
For overcast sky the albedo of the sea surface is always about 
8 per cent. For clear sky the albedo is 3 to 6 ver cent when the 
sun's altitude is greater than 30°, and increases to 20 per cent as 
the altitude decreases from 30° to 12°. . For clear sky the albedo 
increases still further as the altitude falls below 12° if the sea 
me glassy, but it is probably never more. than 20 per cent when the 
sea is rough.* ) 
The average effective albedo throughout the day is therefore 8 
per eant when the sky is overcast. At the equinoxes in clear weather 
with rough water it is about 6 per cent at the ecuator, 7 per cent 
at latitude 40°, 9 per cent at latitude 60°. In clear weather with 
rough water a maximum averace aibedo of about 20 per cent is reached 
in winter in high latitudes where the noon altitude of the sun is not 
more than 12°, 
The solar energy absorbed in a day by one sauare centimeter of 
eh em cnet en A le a A I Ne A Oe RN He EN NR NR A RL SAR mem a me ae ere 
(Kimball, Monthiy Weather Review, Vol. 55, vage 394, 1929. 
Powell and Clarke, Journal of the Optical Society of Americay Yol.26, 
ppe 111-120, 1936. 
