590 EIGHTH PACIFIC SCIENCE CONGRESS 



In order to derive the residual non-fluctuating currents in this 

 situation, the data have been calculated as 48-hour running means, 48 

 hours being the least common multiple of 16 and 12 hours. If tidal 

 and inertial constituents are present, they should disappear in the 

 averages together with the greater part of those of shorter and random 

 periods. This is admittedly a rather brutal treatment, as any fluctua- 

 tions in the residual current are severely smoothed thereby. However, 

 it has served for the preliminary investigations. 



A serious disadvantage is the fact that the ends of a continuous 

 series of observations may be approached within only 24 hours by aver- 

 aged results, and hence any lengthy break in continuity of the data 

 may leave large gaps in the results. Twenty-four hour groupings also 

 have been tried and are found to remove most of the fluctuations and 

 leave smaller gaps. It is preferred to use 48-hour means where possible, 

 however, since the results will be less ambiguous. 



The results of such a treatment to the data of Cruise No. 7 are 

 shown in Figure 9. The large gap in the data on the northern leg of 

 the cruise is due to the break in continuity occasioned by a short storm. 

 Twenty-four hour means, however, show the residual currents setting 

 south to southwest throughout most of the northern leg, with velocities 

 of the order of 5 to 8 cm/sec. A comparison with Figure 8 shows some 

 similarity of G.E.K. means to the dynamic heights along 48°-30'N but 

 none whatsoever along 50°-30'N. The current pattern is also internally 

 inconsistent, requiring the existence of a region of convergence within 

 the area surveyed, an improbable situation. It appears evident therefore 

 that the G.E.K., in this region, does not always measure the long-term 

 average flows associated with the distribution of mass. The converse 

 might be true in regions where stronger currents are found. 



It is postulated therefore that the currents measured are shallow 

 wind-driven currents of short duration. To test this hypothesis, average 

 wind vectors have been plotted along the course. There is reasonable 

 correspondence along 48°-30', assuming the resulting flow to be 45° 

 to the right of the wind and lagging it by a few hours. In the northwest 

 corner of the survey, there appears to be an inconsistency. However, 

 the northwest storm which appeared two days later at about 130°W 

 longitude may already have been driving water well ahead of it. Along 

 50°-S(y, the agreement with 24-hour average currents (not shown) is 

 good. 



These results showed the necessity of making time studies with the 

 G.E.K. The first studies begun in June 1952, were about one day in 

 length and were made by steaming back and forth over an 8-to- 16-mile 

 course, obtaining G.E.K. fixes enroute. Hydrographic stations to 1,000 



