REPORT ON OCEANOGRAPHY 57 



expanding by diffusion in all directions. From the distribution of pu- 

 mice stones, M. Hanzawa derived an approximate value of eddy dif- 

 fusivity to be 4.8 x lOM.S x 10^ c.g.s. (OM, 4, 1953). 



Theories of Wind-Driven Ocean Circulation 



According to the recent theories of the oceanic circulation, the 

 main source of energy supply to the major current of the ocean is the 

 semi-permanent wind system over the oceans. During the period 1949- 

 53, very active research has been done on this subject, 



T. Ichiye has long engaged in the dynamical research on ocean-cur- 

 rents since 1949 (OM, 1, 1949). In 1950 he discussed the wind-driven 

 currents produced by circular wind system. In this computation he 

 retained the inertia terms and applied the result to the motion of wa- 

 ter produced by a typhoon. He showed that an upwelling must occur in 

 deeper levels (OM, 2, 1950). He also discussed the wind-driven ocean 

 circulation in an ocean taking into account the effect of horizontal 

 mixing. His computation is nearly similar to that of Munk (OM, 2, 

 1950). He also discussed the equation of ocean current involving the 

 inertia terms and solved it for a zonal flow in an asymptotic expansion. 

 By this theory he could show the occurrence of a counter current on 

 the right side of the current looking downstream (KMOM, 8, 1950). 



The same year, Masamori Miyazaki computed the coefficients of 

 horizontal and vertical mixing on both sides of a current of uniform 

 velocity by Gebelain's method and obtained the distribution of ve- 

 locity across the current. He thus concluded that the occurrence of a 

 counter current can be determined by vertical distribution of current 

 velocity (OM, 2, 1950, 53-58). The same year, Miyazaki published a 

 theory of wind-produced zonal current in an ocean completely covering 

 the earth, taking into account the effect of both horizontal and vertical 

 mixing. He could prove that the deviation of current system from 

 wind system decreases, and the subsidence of current with depth in- 

 creases by the presence of horizontal mixing (KMOM, 8, 1950, 41^3). 

 He gave an expression for the coefficient of lateral mixing for a station- 

 ary state and the decaying stage without supply of energy from outside 

 (OM, 2, 1950, 113-116). 



In 1951 Ichiye published two papers on the variation of oceanic 

 circulation. In order to explain the double periodicity found by C. 

 O'D Iselin for the Gulf Strea, he discussed successfully the variation of 

 oceanic circulation accompanying the periodic variation of zonal wind 

 system (OM, 3, 1951). He also computed annual variation of the mass 

 and heat transports in five sections across the Kuroshio and described 

 the mechanism of these changes to the density currents due to the phase 



