INTRODUCTION 



Studies of currents in the northeast Pacific, distant from the North 

 American continent, have been mainly based on interpretation or analysis 

 of observed physical and chemical seawater properties. While these clas- 

 sical techniques provide estimates of the mean and very-low-frequency 

 circulation, direct current measurements are required to determine higher 

 frequency time-dependent motion. Very few direct measurements have been 

 reported in the literature. Reid (1962) and Hendershott (1973) found 

 significant diurnal clockwise rotation in several series of GEK (geomagnetic 

 electrokinetograph) measurements of surface currents near 30°N,125°W. 

 Bathythermograph observations in the surface layer did not show significant 

 diurnal vertical isotherm displacements but did show some indications of 

 semidiurnal internal waves. Using neutrally buoyant Swallow floats near 

 28°H,]39°\'l and 29°N,113°W, Knauss (1962) observed diurnal clockwise 

 rotating currents at depths between 700 m and 3,900 m. Diurnal currents 

 at different depths were not in phase. Bathythermograph (BT) observations 

 by Knauss did not indicate significant vertical displacement of isotherms. 

 Diurnal motions reported by Knauss (1962), Reid (1962), and Hendershott 

 (1973) represent inertial period motion. Current measurements from two 

 moored arrays near 28°N,158°W have been reported (Patzert, Wyrtki , and 

 Santamore, 1970), but the time series of these measurements are too short 

 for statistical analysis. 



The objective of this experiment was the direct measurement of inter- 

 mediate and deep currents over a large area over periods of at least one 

 month. The experiment was not designed as a small-scale study of internal 

 wave characteristics. Guthrie, Burns and Smith (1974) have described some 

 of the data on which this report is based. The results reported herein 

 may later be used as inputs to the design of current measurement programs 

 concentrating on smaller vertical and horizontal scales. These results 

 also will be useful in formulating numerical models to compute intermediate 

 and deep currents in the North Pacific. 



DESCRIPTION OF CURRENT METER ARRAYS 



Currents were measured in deep water far from the Continental Shelf 

 near the center of the eastern gyre of the North Pacific Ocean (fig. 1). 

 Table 1 provides a description of each of the nine arrays. Most arrays 

 were located over nearly level topography, and no arrays were placed 

 close to seamounts. In order to reduce motion effects due to surface 

 gravity waves, each array was supported by a subsurface buoy at a depth 

 of approximately 500 m. A short section of chain attached to the buoy and 

 500 m of wire rope supported the first current meter. The remainder of 

 each array consisted of nylon line with current meters suspended at selected 

 depths. Geodyne model 101 current meters were used on arrays A through 

 C, and Geodyne model 102 meters were used on arrays D through I. The 

 recording interval for all meters was 10 minutes. Each array terminated 

 with an acoustic release, steel dampening disk, and concrete anchor clump. 



Current meter depths in table 1 are based on the assumption that the 

 nylon line stretched 15 percent of cut length for new line and 12 percent 



