344 THE DEEP SEA 



process of the tropical ocean with the powerful boundary layer 

 techniques of modern fluid dynamics. By requiring a turbulent heat 

 flux of the size found here they determined from the equations of 

 motion the depth D, the vertical velocity, and, in part, the varia- 

 tion of the depth D with latitude. The last appears to be a more 

 kinematical than dynamical consequence of the motion. The mean 

 motion of their fluid system can be generated by wind stress, in- 

 ternal thermal circulation, or both. The internal thermal circulation 

 due to gradients in the surface temperature was not included in my 

 idealization. Howev^er, such circulation may play a significant sub- 

 sidiary role in horizontal mixing of the upper tropical waters. It 

 has been suggested that such horizontal mixing may be responsible 

 for the amazing constancy of the ratio D f between 10° X and 

 35° N. In fact, if the north-south horizontal transfer of heat in the 

 tropical ocean is comparable to the total heat flux HA found earlier, 

 it would make the a\'erage value of W e\'en more representative of 

 the actual local vertical velocity. 



I have not mentioned nor included in the idealization the role of 

 salinity in modifying the circulation. I ha\'e not mentioned the im- 

 portant role of the internal wave as a transporter of momentum 

 and as a degrader of energy. Yet it is perhaps this mechanism which 

 decelerates the rotation of the earth-moon system. However, in 

 conclusion, I shall mention that even the simple geometric quan- 

 tity A, the area of the warm layer of the ocean, is an ever changing 

 turbulent process whose dynamics must one day be explored. 



REFERENCES 



Robinson, A., and H. Stommel. 1959. The oceanic thermocline. Telliis, 



11, No. 4. 

 Stommel, H. 1956. /. Geophys. Research, 61, 320. 

 . 1958. The Gulf Stream. University of California Press, Berkeley, 



Calif. 

 Sverdrup, H. U. 1947. Wind-driven currents. Proc. Natl. Acad. Sci. 



U. S., 33, 318-326. 

 Swallow, J., and L. V. Worthington. 1957. Nature, 179, 1183-1184. 



