ON THE VARIATION OF THE KUROSHIO NEAR 

 THE JAPAN ISLANDS 



By D. Shoji and K. Suda 



Hydrographic Office, Tokyo, Japan 



Introduction 

 There have been many investigations concerning the nature of the 

 Kuroshio, but the study on its variation is yet very rare, and the hourly 

 variations of its pass and strength may be said to be almost unknown. 

 In recent years, as the results of oceanographic observations gradually 

 piled up, it was made clear that the ocean currents which have been 

 thought rather stationary, made a comparatively violent variation. But 

 the observations are very poor compared with other scientific fields, for 

 example, with meteorology. The cause or the mechanism of variation 

 of ocean current can not be cleared at the present time. We intended, 

 therefore, in the following only to describe some example of the ob- 

 served variation of the Kuroshio. 



1) A Cold Water Mass off the South Coast of Honshu 

 It was first reported by fishermen in 1934 that a large cold water 

 mass of a diameter of about 100 sea miles appeared off the south 

 coast of Honshu and that the Kuroshio flowed around this cold water 

 mass. According to this report the Hydrographic Office, the Meteor- 

 ological Observatory and the Fisheries Research Institute of Japan 

 made many oceanographic observations in this area (Figs. 1-5). At first 

 this cold water mass (the water temp, at 200 meters was about 10°C in 

 it and the opposite side of Kuroshio about 18°C) was off the Kii Penin- 

 sula, and then moved eastward a little and its existence was confirmed 

 until 1944. Owing to the War the obsei^ation was interrupted, and 

 when reopened in 1946 the cold water mass was much contradicted, and 

 then disappeared. Hereafter, the cold water mass appeared in winter 

 of 1946-47, 1950-51 and 1952-53 in this area, but it did not so devel- 

 op, and the appearance of this cold water mass seems to be a seasonal 

 phenomenon in recent years. It is clear from the T-S diagram and other 

 evidences that this cold water mass is a consequence of the upwelling 

 of the cold intermediate water. But why this upwelling happens so 

 extensively and why the Kuroshio runs around this, departing from the 

 Japanese coast, has not been satisfactorily showtL It is true that the 



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