FISHERY BULLETIN: VOL. 72, NO. 4 



90° 80° 70* 



I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I ij 30' 



110° 100° 



Figure 5. — Geopotential anomaly, in joules per kilogram (dynamic decimeters), at the sea surface relative to 500 db in October- 

 November 1967. EASTROPAC cruise David Starr Jordan 50. The position of the intertropical convergence zone at the eastern and 

 western ends of the map is indicated by triangles. 



7) is much like that in February- April 1967 (Fig- 

 ure 1). In 1968 the Countercurrent is present be- 

 tween lat. 4° and 7°N at long. 119°, 112°, and 

 105°W, but is not found at long. 98° and 95°W. 

 Farther east at long. 88° and 85°W the Counter- 

 current is strongly developed along lat. 5°-8°N be- 

 tween cyclonic and anticyclonic eddies similar to 

 those observed in 1967. 



By June-July 1967 (Figure 3) the North 

 Equatorial Countercurrent is well established 

 between lat. 6° and 10°N on all four meridional 

 sections. In Figure 3 a weak eastward current, 

 separated from the Countercurrent by a narrow 

 band of westward flow, can be seen about 200 km 

 south of the southern boundary of the Counter- 

 current. This secondary countercurrent repre- 

 sents a surfacing of a narrow but stable sub- 

 surface eastward current, which has its maximum 

 speed at a depth of 50-200 m just south of the 

 North Equatorial Countercurrent (Tsuchiya, 

 1972). 



In August-September (Figure 4) the North 

 Equatorial Countercurrent is fully developed and 

 extends east to the coast of Costa Rica, where it 

 turns to the northwest along the coast. In these 

 months the Countercurrent is wider and is lo- 

 cated farther north than in the February-April 

 periods of 1967 and 1968. In August-September it 

 lies between lat. 7° and 11°N at long. 119° and 

 112°W and between lat. 5° and 10°N east of long. 

 105°W (Figure 4). About the same condition con- 

 tinues through November (Figure 5), although 

 the ITCZ starts shifting south in October. In 

 December-January (Figure 6) the Countercur- 

 rent starts moving south, following the ITCZ's 

 southward shift, which began 2 mo earlier. 



The variation of the North Equatorial Coun- 

 tercurrent revealed by the present maps of geopo- 

 tential anomaly generally agrees with the results 

 of set-and-drift observations discussed by Puis 

 ( 1895), Cromwell and Bennett ( 1959), and Wyrtki 

 (1965). 



1082 



