Smith 



Tow patterns for current determinations were scheduled for 

 changes and at the leg mid-points but because of some equipment 

 problems in this first attempt to use current meters mounted on the 

 chain, not all schedules were kept. Figure 7 shows current vectors 

 at 43 feet referenced to 75 feet in the region of the cyclonic eddy. 

 The 250- foot depth contour of the 25° C isotherm shows the relative 

 position of the eddy. The current velocity is the greatest nearshore 

 (1. knot). This is probably caused by the addition of the eddy tan- 

 gential velocity and the velocity of the water flowing northward along 

 the obstruction after breaking off from the main westerly flow. The 

 average peripheral current, at 60- mile radius, is 0. 6 knot. At 

 distances slightly greater than 60 miles from the center, the tangen- 

 tial velocity is about 0. 3 knot. Near the eddy center, 15-mile radius, 

 the current is about 0. 3 knot also. Therefore, the velocity distribu- 

 tions are similar to those of a Rankine vortex which has a velocity 

 (v) proportional to a distance, r, in an inner region and to r~^ in an 

 outer region (Lamb, 1945). 



CRUISE 36, 1966 



In July 1966, again the thermal structure profile was recorded 

 and direct current observations were made in the area southwest of 

 Alenuihaha Channel (Maui-Hawaii). In the region that had been occu- 

 pied by a single cyclonic eddy in 1964, two smaller eddies were found, 

 one cyclonic near shore and the second anticyclonic and west of the 

 first. Both eddies were elliptical in shape as shown by the average 

 depth contours of the 25 C and 23 C isotherms of figures 8 and 9, 

 respectively. The anticyclonic eddy is typified by the "dish" or 

 depression in the temperature structure, which is indicative of 

 clockwise rotation in the northern hemisphere. The major axis of 

 this eddy is about 90 miles, and the minor axis about 60 miles. The 

 cyclonic eddy is slightly smaller, major and minor axes being about 

 80 miles and 50 miles respectively. 



The temperature structure for the track leg E to F (fig. 10) 

 clearly shows the "dome" and "dish" generated by the counter- 

 rotating eddies. A strong horizontal temperature gradient, 0. 2 C/ 

 mile, at 300 feet persists for more than 20 miles in the region of 

 eddy confluence. The rotation effects of the eddies reach to depths 

 greater than 750 feet at the eddy centers. The 26° C isotherm is 

 forced to the surface by the upwelling of the colder water at the 

 center of the cyclonic eddy, but the same isotherm is drawn down 

 to more than 400 feet by the convergence of warm water at the cen- 

 ter of the anticyclonic eddy. Hence, a depth change of 400 feet for 

 the 26° C isotherm occurs over 50 miles to the east and 30 miles to 

 the west of the area of confluence. A small pocket of 26 C water 

 can be seen shoreward of the dome. Both eddies appear symmetric 

 about a vertical center. The small-scale vertical variations are of 

 about the same dimensions as those observed in 1964. A few inter- 

 mediate-scale vertical variations are evident in the structure. 

 Coherent depth changes of isotherms can be observed throughout 



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