A CONTRIBUTION TO THE THEORY OF UPWELLING 

 AND COASTAL CURRENTS * 



By Koji HiDAKA 



Geophysical Institute 

 Tokyo University, Japan 



I. Introduction 



There have been several descriptions of the upweliing noticed off 

 California, Peru, West Africa and other coasts by Thorade (1909), 

 McEwen (1912, 1929), Gunther (1936), Defant (1936, 1952), Sverdrup 

 (1931, 1938) and Sverdrup and Fleming (1941). The explanation of 

 this process given by Sverdrup in 1938 is worth attention. According 

 to Sverdrup and Fleming, it is known from the analysis of the water 

 masses that the ^\'ater taking part in the process of upweliing off the 

 coast of Southern California originates mostly in the layers from 200 

 to 300 meters beloAv the surface. These are, ho^vever, all qualitative 

 discussions and it has been as yet not possible to explain this phenome- 

 non theoretically and predict the velocity and width of the coastal cur- 

 rents produced by the prevailing winds. Very recently Defant (1952) 

 made a theoretical explanation assuming a sea consisting of two layers 

 of water with different densities. The present research is an attempt 

 to solve this problem mathematically and to draw some quantitative 

 conclusions concerning this process, which is very important in all fields 

 of oceanography. 



The explanation of the upweliing seems to be satisfactory only by 

 treating this problem thermodynamically as well as hydrodynamically. 

 The following discussion will, however, be made only from a purely 

 hydrodynamical standpoint, on the assumption that the seawater is of 

 uniform density. This is a necessary consequence for simplifying the 

 mathematics, but the author believes to have been able to obtain some 

 results which are consistent wdth certain facts observed in this process. 



It has been noticed that the upweliing takes place most favorably 

 when, in the northern (southern) hemisphere, a wind blows in such a 

 manner that the coast is on the left-hand (right-hand) side of an ob- 

 server who looks in the direction of the wind. Thus the upweliing oft 

 the coast of California is most remarkable in early summer wh'^n north- 

 westerly winds prevail for several weeks nearly parallel to the coast. 



* Published in the Transactions American Geophysical Union. June 1954, 

 p. 431-444. 



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