REPORT ON OCEANOGRAPHY 59 



that the result agrees satisfactorily with the observations near the equa- 

 tor. In this region the relative current is much stronger than the pure 

 drift current, while the meridional components of currents are negli- 

 gibly small compared with the EW-components (JOSJ, 8, 1952, 15-22). 



The dependence upon the bottom friction of sea surface slope in- 

 duced by wind is discussed theoretically by Ichiye. He determined the 

 vertical structure of drift currents and compared it with actual obser- 

 vations. He also obtained the drift current when Rossby's expression 

 for the vertical mixing coefficient is used (KMOM, 10, 1952). 



Recently K. Yoshida treated successfully the problem of circula- 

 tion in the upper mixed layer in the equatorial region of the North 

 Pacific Ocean by solving the steady state equations involving terms of 

 Coriolis forces, pressure gradient, and horizontal as well as vertical mix- 

 ing (Hoshida, Han-lee Mao, and Paul L. Horro, in press). 



The most part of the theories described above is obtained on the 

 assumption that the inertia terms in the dynamical equations are neg- 

 ligibly small compared with the remaining terms. The significance of 

 these terms in dynamical oceanography was discussed by Hidaka and 

 M. Miyoshi (GN, 2, 1949). A similar discussion was made by Ichiye, 

 who concluded that these terms cannot be neglected when the curl of 

 the wind stress is large, and estimated their magnitude (OM, 2, 1950). 



The simplification of the theory of the wind-driven ocean current 

 will be approached by assuming a zonal ocean and a planetary wind 

 system so that both winds and currents are independent of longitude. 

 Theories were worked out by Hidaka and his collaborators K. Takano 

 and M. Tsuchiya (GN, 3, 1950; GM, 23, 1952, 487-495; JMR, in press). 



A very important question in dynamical oceanography is how and 

 in what proportions the energy of wind is imparted to raising waves 

 and producing currents. This problem was discussed by K. Yoshida 

 (JOSJ, 7, 1951) and Ichiye (OM, 4, 1952). 



In 1952 K. Kajiura discussed on the currents and the accumula- 

 tion of water produced by winds in the water consisting of two layers 

 of different densities. He assumed that the eddy viscosity is negligible 

 along the boundary of two layers and showed that the shape of the 

 boundary surface agrees very closely with observations (JOSJ, 8, 1952, 

 67-71). 



Upwelling and Coastal Currents 



Recently K. Hidaka propounded a hydrodynamical theory of up- 

 welling. He assumed an infinitely long straight coast and constant 

 latitude, and discussed the upwelling to be produced as the effect of 

 wind blowing in a belt of a certain width from the coast. He took the 



