58 



THE HEAT BUDGET OF THE OCEANS 



the surface and 1 m would increase in the clearest water by 6.24°, and 

 in the most turbid water, by 7.72°. Between 20 and 21 m the correspond- 

 ing values would be 0.04° and 0.0003°. 



The temperature changes recorded in table 9 show no similarity to 

 those actually occurring in the open oceans, where processes of mixing 

 entirely mask the direct effect of absorption, but in some small, land- 

 locked bodies of water the temperature changes at subsurface depths may 

 be governed mainly by absorption of short-wave radiation. 



Effective Back Radiation from the Sea Surface. The sea 

 surface emits long-wave heat radiation, radiating nearly like a black body, 

 the energy of the outgoing radiation being proportional to the fourth 

 power of the absolute temperature of the surface. At the same time the 

 sea surface receives long-wave radiation from the atmosphere, mainly 

 from the water vapor. A small part of this incoming long-wave radiation 



Table 9 



TEMPERATURE INCREASE IN °C AT DIFFERENT INTERVALS AND IN 

 DIFFERENT TYPES OF WATER, CORRESPONDING TO AN ABSORP- 

 TION OF 1000 G CAL/CM2 



is reflected from the sea surface, but the greater portion is absorbed in a 

 small fraction of a centimeter of water, because the absorption coefficients 

 are enormous at long wave lengths. The effective hack radiation from the 

 sea surface is represented by the difference between the '' temperature 

 radiation" of the surface and the long-wave radiation from the atmos- 

 phere, and this effective radiation depends mainly upon the temperature 

 of the sea surface and the water-vapor content of the atmosphere. 

 According to Angstrom the latter can be put proportional to the local 

 vapor pressure, which can be computed from the relative humidit}^ if the 

 air temperature is known. Over the oceans the ah temperature deviates 

 so little from the sea-surface temperature that the vapor pressure can be 

 obtained with sufficient accuracy from the sea-surface temperature and 

 the relative humidity of the air at a short distance above the surface. 



