were used in computing stresses. Figures 40 and 41 are based on a drag coefficient of 

 0.0012 and twice-daily reports of atmospheric pressure. 



The flow patterns as computed vary with the method of calculating stresses and 

 particularly marked differences in these computed patterns occur in high latitudes. Com- 

 parison of figure 38 with figure 39 shows that alternative methods of computing mean 

 stresses give apparent velocities in opposite directions north of 45°N. However, when 

 both the drag coefficient and the method of obtaining mean stresses were changed (figs. 

 40 and 41), the resulting velocities at equal levels were but little different up to 45°N from 

 those indicated in figures 36 and 38. It should be noted that Ekman divergence is not 

 considered in figures 36 and 38, and its significance is discussed in a following section. 

 The use of 0.0026 as the drag coefficient resulted in values for stress that apparently were 

 too large, but calculating stress values from a monthly mean of pressure distribution rather 

 than estimating stresses from twice-daily reports of pressure and then taking a monthly 

 mean led to stress values that apparently were too small, and these discrepancies tend to 

 cancel one another. 



3.1.3 Velocities in 1963. — The oceanographic data for 1963 are presented in the same 

 manner as the 1961 data. Figures 42 through 47 are of geopotential topography adjusted 

 to wind-driven geostrophic transport with consideration of Ekman divergence. The 

 wind-driven transport is based on a drag coefficient of 0.0026, and the mean pressure 

 distribution for May 1963 is used. As in the 1961 results, flow was mainly zonal. North 

 of 40° N, the flow at 250, 500, and 1,000 meters was easterly. Velocities decreased from 

 about 3 cm/sec at 250 meters to less than 1 cm/sec at 1,000 meters. From 40° to 30° N, 

 flow was southerly. At 500 meters, flow was easterly or northeasterly north of 30° N; it 

 was southwesterly south of 30° N. At the 1,000-meter level, the flow south of 40° N was 

 poorly defined in the 1963 data, though there were indications of a cyclonic flow centered 

 at about 35° N, 180°. South of 28° N, there was a weak westerly set. At 2,000 meters, 

 flow was weak over most of the area and there is some indication of an anticyclonic cir- 

 culation centered near 35° N, 180°. The patterns of the flow at 4,000 and 5,000 meters 

 were similar to each other. North of 45° N, velocities at these depths were of the order 

 of 1 cm/sec westerly, and were the largest found at or below 4,000 meters in 1963. Be- 

 tween 45° and 40° N, the flow was easterly, shifting to southerly south of 40° N. 



Flow at the deep levels tended to conform to the salient features of the bottom topog- 

 raphy. This tendency — more obvious at 5,000 meters (fig. 47) than at 4,000 meters (fig. 

 46) — was exhibited near the bathymetric feature at 30°N, 162°W, near the Aleutian Trench, 

 and in the vicinity of the Hawaiian Island Rise. Throughout much of the area, circulation 

 at 4,000 and 5,000 meters was opposite to that above 1,000 meters. 



Figure 48 depicts the dynamic topography adjusted to the May 1963 wind-driven 

 geostrophic transport in which the Ekman divergence is neglected. Differences between 

 the flow patterns shown in figure 48, which neglects Ekman divergence, and figure 47, 

 which includes consideration of Ekman divergence, were not significant. 



At the northern limit of the area, near the Aleutian Islands, the dynamic topography 

 suggests a boundary current in a direction opposing the flow at lower latitudes. In this 

 region of high lateral friction, details of current patterns are open to some question as the 

 method of computing wind-driven transport used is an approximation applicable to central 

 ocean areas. 



Figures 49 through 54 depict the dynamic topography adjusted to wind-driven geo- 

 strophic transport which was determined from the May 1963 mean of stresses calculated 

 from twice-daily reports of pressure, using a drag coefficient of 0.0012. Results were 

 similar to those shown in figures 42 through 47 (based on the higher drag coefficient and 

 an alternative method of estimating mean values as discussed previously). The more 

 accurate determination of wind-driven transport suggests a slightly weaker flow at the 

 1.000 meter level south of 40° N. 



11 



