SECT. 3] 



EQUATORIAL CURRENT SYSTEMS 



239 



eastward -flowing Cromwell Current flows below the South Equatorial Current. 

 Secondly, the existence of the Cromwell Current strongly suggests that the as- 

 sumptions of the Sverdrup model (namely the dropping of all the nonlinear 

 terms) are not justified in the vicinity of the equator. 



There are two other areas where the transport calculations in Fig. 3 disagree 

 with the surface current in Fig. 1. The first is the position of the northern edge 

 of the North Equatorial Current in January. Although the Deutsche Seewarte 

 chart shows the northern edge of this current farther south in winter than in 

 summer, the southward movement is to a latitude closer to 20-22°N rather 



Fig. 3. ".Sverdrup" transport in the tropical Pacific for January and July. Dark areas 

 indicate eastward transport, light areas westward transport. Each line represents 

 3 x 10 6 tons /sec. 



than 17°N as indicated in Fig. 3. The second area of disagreement is the indica- 

 tion of a weak eastward transport at about 15°N and east of 140°W during July. 

 Although it is doubtful that such a reverse flow extends as far west as 140°W, 

 there appears to be a growing body of evidence (as yet unpublished) of an 

 eastward transport east of 120°W. 



3. A Two-Layer Ocean — The Thermocline 



The equatorial oceans are characterized by a layer of warm, well-mixed water 

 separated from the colder intermediate and deep water by a narrow zone of 



