Poy yee 
the ocean may thus be estimated by first taking the appropriate 
value from Table 5. This is then reduced for the average cloudiness 
during the hours the sun is high in the sky. The resulting value 
may then be corrected for the albedo of the sea surface. 
Nocturnal radiation 
Since the ocean is very nearly an ideal radiator the only dif- 
ficulty in estimating nocturnal radiation is in finding the radiation 
from the atmosphere. Water vapor and clouds are by far the most im- 
portant absorbers and radiators of long-wave radiation in the atmos- 
phere. In clear weather, therefore, the long-wave radiation re- 
ceived at the sea surface depends on the vertical distribution of 
water vapor and of temperature in the atmosphere. 
From surface observations there is no direct means of estimating 
these distributions. It has however been found that vapor pressure 
at deck level serves as an apvroximate index of the effect of these 
distributions on nocturnal radiation. Table 6 has been computed to 
give the nocturnal radiation as a function of sea-surface temperature 
and of vavor pressure at deck level. In addition the emission of an 
ideal radiator is shown for each temperature. 
The nocturnal radiation is reduced by clouds. Their effect de- 
pends on their temperature and density. To obtain a rough evaluation 
of nocturnal radiation with overcast skies one may tale the following 
percentages of the appropriate value in Table 6: 75 per cent for 
cirrostratus, 35 per cent for altostratus, 15 per cent for stratus 
Ox Numbostratus. 
Mixing in the air above the sea surface 
Next to the sea surface the vapor vressure has its equilibrium 
