In general, the average surface density decreases from east to 

 west and south to north. Thus, remembering that in the northern hemi- 

 sphere the light water is to the right of an observer facing in the direc- 

 tion of flow, the density distribution suggests that the contribution to the 

 net surface flow is a relative current setting southeast. 



Surface circulation 



For cruise 21 dynamic calculations are limited to the upper 

 500 m. These depths (500 m. ) are approximately the depths of the 

 salinity minimum during this cruise. A considerable part of the con- 

 tribution toward the surface flow due to the intermediate distribution 

 of mass is therefore not shown. This, however, is not expected to 

 change materially the presentation of the main features of the circulation. 



The dynamic topography at the surface relative to the 500-m. 



level (fig. 29) shows that the survey region is again one with a complex 



flow pattern. There appear in the lee of the islands three vortices. 



Two of these, centered in the vicinity of stations 47 and 51, show a 



counterclockwise rotation, and the larger, third vortex, centered in 



the vicinity of 20 N. , 158 W. , shows a clockwise rotation. Highest 



current speeds in the order of 1 to 2 knots occur again on the periphery 



of the vortices. In the northern section of the survey region an easterly 



o o y o 



current turns south between 157 and 158 W. and then flows west just 



north of the island chain. North of Hawaii a southwesterly current enters 



the survey region and is deflected to the southeast off the island's coast. 



The circulation about the island of Hawaii is clockwise. 



Geomagnetic Electrokinetograph (GEK) observations 



The GEK surface current vectors are plotted in figure 30. The 

 arrows indicate the direction of flow and numbers the speed in cm. /sec. 

 All observations were made with unfloated electrodes and subsequently 

 corrected for the "droop" effect. 



As before, no detailed analysis is made, but when figures 29 and 

 30 are compared, agreement between GEK and geostrophic current direc- 

 tion and relative speed is apparent. High GEK speeds occur between the 

 major vortices of figure 29, and the directions there as well as in regions 

 of lower current speed are in good agreement. Interesting to note is the 

 agreement between the GEK currents and the geostrophic current in Kauai 

 Channel. Both figures 29 and 30 show northwesterly flow in the eastern 

 part and southwesterly flow in the western part of the channel. 



21 



