588 



Basic Principles of the General Oceanic Circulation 



Fig. 268. The oceanic mass transport of the North Pacific Ocean, derived from data 

 available. Between two neighbouring stream lines 6 million tons of water flow per second. 

 (1) Kuroshio; (2) Oyashio; (3) Alaska Current; (4) California Current; (5) Sub-Antarctic 

 Current; (6) North Pacific Current; (7) East Pacific Vortex; (8) North Equatorial Current. 



deduced from oceanographic observations, and this agreement is confirmed by all 

 investigations that have been carried out along the lines of Munk's computations. 

 HiDAKA (1950, a, b, c, 1951) has dealt in particular with the wind-generated ocean 

 circulation of the Pacific and has obtained an overall climatological oceanic circula- 

 tion, that fits admirably with that deduced from ship's displacements. His mathe- 

 matical treatment of the problem differs from that used by Munk only in taking 

 higher order terms into consideration and in using infinite series for the solution of 

 the differential equation, in some instances with spherical co-ordinates, while Munk 

 and his collaborators have used planar co-ordinates. More recently, Hidaka (1955) 

 has presented a detailed numerical theory of the general circulation of the Pacific 

 which he regards as a purely wind-generated phenomenon. He uses the assumption 

 that the vertical velocity vanishes exactly at all points. Further, he gives the horizontal 

 distribution of the stream lines for different subsurface levels. These circulation 

 patterns are all similar to the sea surface circulation. The only noticeable difference is a 

 general reduction in intensity of the movement with depth. It may be already as little 

 as half the surface intensity in 250 m depth. His numerical results are, however, 

 difficult to interpret on a physical basis, and appear insufficient for an explanation of 

 the vertical mass transports necessary for continuity. 



Hansen (1951, 1954) treated the circulation problem as a boundary value problem 

 ("Eigen" value problem). His method is equally suitable for finding the volume trans- 

 port and the form of the sea surface in an enclosed part of the ocean from the known 

 wind field. Hansen calculated the volume transport and the sea surface topography for 

 the equatorial part of the Atlantic from the average August wind field, and obtained 

 a satisfactory agreement with results based on observations of ship's displacements 

 and of the density distribution. 



While for all methods the agreement is very good qualitatively, this is not always so 

 quantitively. Munk, for instance, obtained transport values for the Atlantic and the 

 Pacific which were only half as great as those computed from observational data 

 (36 and 39 x 10^ m^/sec for maximum transport by the Gulf Stream and the Kuroshio, 

 respectively, against observed mean values of 55 to 74 and 65 x 10^ m^/sec, res- 

 pectively). It is not improbable that the discrepancy arises from the fundaments of the 

 theory, possibly from the use of the mean wind stress based on climatological wind 



