Discussion 

 The preceding computations suggest that the vertical component 

 of the background turbulent motion in deep ocean has a typical velocity 

 less than 0.2 cm sec , a displacement of more than 50 cm and a fluctu- 

 ation time greater than 250 sec. Corresponding figures for the hori- 



-1 5 



zontal fluctuations are 2 cm sec , 5km , and 2x10 seconds. 



These figures were based on the assumption that the turbulence is gener- 

 ated by comparatively steady shear flows in the ocean for which the 

 Richardson's number does not exceed 0.1. They are consistent with 

 observed diffusion rates and the maximum possible rate at which external 

 forces at the boundaries of the ocean could supply energy to maintain the 

 motion. 



The requirement on the Richardson's number is a stringent one. 

 It can be criticized as applying to a developed shear flow and not to 

 uncertain oceanic conditions. In fact, other observers have reported 

 numbers ranging from 10 to 100 . Reference should be made to Townsend 

 (1958) for a discussion of this point. 



If the Richardson's number is assumed to be 10 instead of 0.1, 

 the shear velocity gradients would be one-tenth as large and the vertical 

 velocities would be reduced by a factor of about 3 . Both the length 

 and time scales would increase. The smaller Richardson's number was used 

 in the preceding computations so as to obtain an upper limit for the 

 velocity fluctuations. 



It was necessary to attribute horizontal diffusion to a horizontal 

 eddy structure. The origin of this motion remains unknown. It is possible 



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