638 The Tropospheric Circulation 



close to the continental shelf. The tendency towards a formation of meanders appears 

 only after the Gulf Stream leaves the continental shelf, but probably there are other 

 factors that will decide about the development of meandering motion than the distance 

 from the continental shelf. 



As yet no fully satisfactory explanation has been given for the observed split of the 

 Gulf Stream into a number of branches. Hansen (1952) has demonstrated that under 

 certain conditions a northwards flowing current while turning towards the east can 

 break up into several branches; but his solution is of more formal character and no 

 actual reasons can be offered for this phenomenon. 



{e) The Kuroshio 



The three-dimensional structure and the dynamics of this current have been 

 investigated by Uda (1930), Sigematsu (1933) and Kisindo (1934) on the basis of 

 series observations made by the hydrological department of the Japanese Marine and 

 the Imperial Fisheries Experimental Station in Tokyo (since 1925) and also by the 

 oceanographic survey vessel "Mansyu". A number of transverse profiles have been 

 prepared and critically worked with by Wust (1936a) in a comparative study of the 

 Kuroshio and the Gulf Stream and further valuable work has been performed by 

 KOENUMA (1939). Wiist has dealt with a cross-section at right angles to the chain of 

 islands, the Ryu-kyu, from 27° to 29° N., just before the Tsusima current splits into 

 branches and with another cross-section farther north (little to the south of Shiono 

 at Misaki, the south cape of the projecting Kii peninsular at about 30° to 34° N.). 

 See Fig. 261 for the position of these sections. 



The inclination of the isolines of the oceanogi-aphic factors forced by the water 

 movement appears clearly in all cross-sections through this strong current. A com- 

 parison with conditions in the Gulf Stream shows that there is an almost identical 

 thermal structure but considerable differences occur in the salinity distribution; the 

 Kuroshio has a low salinity 34-32 to 34-98%o and a very weak vertical salinity stratifi- 

 cation, while the Gulf Stream possesses considerably higher salinity (34-97-36-65%o) 

 and a pronounced stratification. The Kuroshio region also shows an intermediate 

 salinity minimum at 500-800 m depth resulting from an intrusion of the weakly 

 saline sub- Arctic intermediate water flowing in from the north (p. 172). 



Figures 298 and 299 show the temperature and salinity distributions in the Ryu-kyu 

 section (Feb. 1927) and in the Shiono-Misaki section (Jan. 1927). Disregarding the 

 top layers, the sections for the summer months show entirely similar conditions. 

 These sections have also certain similarities with those through the Gulf Stream (see 

 Figs. 282, 283). 



The Ryu-kyu section corresponds closely to that through the Florida Strait, the 

 Shiono-Misaka section to the Chesapeake Bay transverse section. It is also apparent 

 from these sections that the Kuroshio is throughout the entire vertical extent a weakly 

 saline current as compared with the Florida Current; the highly saline core layer can 

 again be explained as a distant effect of the tropospheric circulation of the subtropics 

 and tropics. The velocity distribution calculated from the mass field of the Ryu-kyu 

 winter section shows maximum intensities of 61 cm/sec below the sea surface at 

 150 m depth. In summer highest values of about 90 cm/sec occur at the sea surface. 

 The weakening and downward displacement of the current maximum in winter is in 



