TSUCHIYA: SURFACE GEOSTROPHIC FLOW 



130" 120° no 



30' 



I I I I I I I I I I I I U I I I I I 



,! ' I ' I ' I ' I M ' I ' I ' 1 1 1 M 1 1 ' I ' 1 1 1 1 1 1 M 



Geopotential Anomaly, J/kg 



db Over 500 db 



April -May 1967 



20' 



10° 



0° 



10° 



1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 i 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 L 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 



iiii Iiiiiiiii- 



130° 



120° 



110° 



100° 



90° 



80° 



70° 



Figure 2. — Geopotential anomaly, in joules per kilogram (dynamic decimeters), at the sea surface relative to 500 db in April-May 

 1967. EASTROPAC cruise, Dai'jc? Starr Jordan 20. The position of the intertropical convergence zone at the eastern and western ends 

 of the map is indicated by triangles. 



to draw isopleths. Consequently, the deduced, 

 geostrophic-flow pattern is not everywhere reli- 

 able. Nevertheless, the general trend of flow indi- 

 cated by the present maps is parallel to the coast 

 and toward the equator. There is not much change 

 in general flow patterns during the EASTROPAC 

 period. 



Eastern Boundary Currents in 

 the Northern Hemisphere 



In this region flow also tends to follow the 

 coastline. On the map for February-March 1967 

 (Figure 1), there is an indication of a northward 

 current, the Colombia Current (Wooster, 1959; 

 Stevenson, 1970), flowing close to the coast of Co- 

 lombia toward the Gulf of Panama. On the maps 

 for August-September 1967 and February- April 

 1968 (Figures 4 and 7) the distribution of stations 

 is inadequate for defining the Colombia Current. 



Off Costa Rica the direction of flow varies, de- 



pending on the development of an anticyclonic 

 eddy farther offshore. The strong southeastward 

 flow indicated by the map for February-March 

 1967 (Figure 1) is associated with the northern 

 edge of an anticyclonic eddy centered at lat. 5°N, 

 long. 85°W. A similar anticyclonic eddy is ob- 

 served in February-April 1968 (Figure 7), but is 

 centered at lat. 5°N, long. 88°W, farther west 

 than in 1967; and the flow near the coast of Costa 

 Rica is northwestward. As Puis (1895:24 and 27), 

 Cromwell (1958), and Wyrtki (1965) have noted, 

 their drift charts also show a well-developed an- 

 ticyclonic eddy in this area from February to 

 March. This anticyclonic eddy seems to be a nor- 

 mal feature in these months. In August- 

 September (Figure 4), when no such anticyclonic 

 eddy develops, the area off the coast of Costa Rica 

 is dominated by the northwestward return flow of 

 the North Equatorial Countercurrent. 



A cyclonic circulation is well developed around 

 the Costa Rica thermal dome centered near lat. 



1079 



