26 PHYSICAL PROPERTIES OF SEA WATER 



320 g cm/sec, was found in a homogeneous surface layer within which one 

 can expect the eddy diffusivity to equal the eddy viscosity. This value 

 is probably the only one that is as great as the corresponding eddy 

 viscosity. Otherwise, the eddy diffusivity is smaller, in agreement with 

 the fact that generally stable stratification is encountered. From the 

 remarks in the table it is evident that the eddy diffusivity increases 

 with increasing velocity of the currents and decreases with increasing 

 stability, in agreement with the preceding considerations. 



The results of a few determinations of horizontal eddy coefficients, 

 fie,h and jjLs.h, are given in table 3. The values of the coefficients have 

 been derived by making bold assumptions and can be considered as 

 indicating only the order of magnitude. This order of magnitude depends 

 upon the size of the area from which observations are available, which 

 probably explains why the value from the California Current is much 

 smaller than the values from the Atlantic Ocean, where conditions 

 within much larger regions have been considered. The latter values, 

 which have been obtained partly from observations at or near the surface 

 and partly from observations at great depth, agree remarkably well. 

 No relation appears between the average velocity of the currents and 

 the eddy coefficients or between the stability and the coefficients. Simi- 

 larly, from the meager evidence available, the eddy viscosity and eddy 

 diffusion appear to be equal, and therefore the processes of horizontal 

 turbulence seem to be entirely different from those of vertical turbulence, 

 but it should be borne in mind that the study of horizontal turbulence in 

 the ocean is at its very beginning. 



Absorption of Radiation 



Absorption Coefficients of Distilled Water and of Pure Sea 

 Water. In water the intensity of parallel beams of radiation of wave 

 length X decreases in the direction of the beams, the decrease in a layer 

 of infinitesimal thickness being proportional to the energy, 7x, and to the 

 thickness of the layer: 



dh= -kJ^z. (11,10) 



The coefficient of proportionality, kx, is called the absorption coefficient 

 at the wave length X. Integrating equation (II, 10) between the limits 

 X = h and x = h + L, one obtains 



2 30 



K\ = -^ [log h,h - log I\,h+L], (II, 11) 



■where the factor 2.30 enters because base- 10 logarithms are used instead 

 of natural logarithms, and where L is the thickness of the layer within 

 which the energy of the radiation is reduced from I\,h to I\,h+L. The 

 latter equation also serves as a definition of the absorption coefficient. 



