TSUCHIYA: SURFACE GEOSTROPHIC FLOW 



130° 120" 110 



30' 



-iMI'|i|i|i|'IMMi 



20' 



10° 



10° 



1 1 1 1 1 1 1 ' M 1 1 m 30' 



Geopotential Anomaly, J/kg 



db Over 500 db 



December 1967- January 1968 



-I I I I I I I I i I I I I I I I I I 



lilililililiM 'I'I'l I'I'li 



70° 



130° 120° 110° 100° 90° 80° 



Figure 6. — Geopotential anomaly, in joules per kilogram (dynamic decimeters), at the sea surface relative to 500 db in December 

 1967-January 1968. E ASTROPAC cruise David Starr Jordan 60. The position of the intertropical convergence zone at the eastern 

 and western ends of the map is indicated by triangles. 



North Equatorial Current 

 Region 



North of the North Equatorial Countercurrent, 

 the North Equatorial Current is found on all 

 seven maps (Figures 1-7). On the maps for 

 February-March 1967 and February-April 1968 

 (Figures 1 and 7) the westward flow of the North 

 Equatorial Current starts off the Gulf of Tehuan- 

 tepec with a major contribution of water coming 

 from the northwest along the Mexican coast. 

 Water coming, from the southeast appears to re- 

 turn to the east forming a cyclonic eddy around 

 the Costa Rica thermal dome. 



In February-March 1967 (Figure 1) the North 

 Equatorial Current is interrupted by a continu- 

 ous eastward flow indicated along lat. 15°N from 

 long. 126°W to the coast of Mexico, where it turns 

 to the south to feed the North Equatorial Cur- 

 rent. This eastward flow is broadly developed at 



long. 112°W and extends from lat. 10° to 18°N. 

 There is a suggestion that a similar eastward 

 flow is present in April-May 1967 and 

 February- April 1968 (Figures 2 and 7). Reid's 

 (1961) map of the surface geostrophic flow also 

 indicates an eastward current at about the same 

 latitude from long. 130° to 95°W, but his data in 

 this area are principally from northern fall and 

 winter. The surface drift charts (Puis, 1895; U.S. 

 Navy Hydrographic Office, 1947) do not show 

 such an eastward flow west of long. 110°W, possi- 

 bly because of the westward Ekman drift and 

 leeway of ships due to the strong northeasterly 

 trades. 



On the map for August-September (Figure 4) 

 the North Equatorial Current starts off the coast 

 of Costa Rica. East of long. 100°W it is fed almost 

 entirely by the return flow of the North Equator- 

 ial Countercurrent, which is fully developed in 

 these months. 



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