CIRCULATION NEAR THE WASHINGTON COAST 593 



later date. The amplitude of the semidiurnal constituent on Cobb Sea- 

 mount is about 15 per cent less than the G.E.K. results, which is the 

 same as the change in the mean tidal range at Astoria during the two 

 periods. The change in the inertial component may arise from an in- 

 crease in average wind velocity from about 8 to 20 knots over the same 

 period. 



The results of the time study in June 1953, are shown in Table 

 II. Although the amplitudes are smaller, the relative importance of the 

 16- and 12-hour constituents is supported. This experiment was carried 

 out at 48°-02'N, 130°-29'W; and by chance during the time study, the 

 ship drifted over and charted a new seamount rising to a least depth of 

 280 fathoms. This shallowing of the water may have had some effect 

 upon the G.E.K. 



The possibility exists that internal waves of tidal and inertial period 

 give rise to the currents or effects measured by the G.E.K. This has 

 been investigated by a study of the bathythermograms taken to a depth 

 of 450 feet during the time study of Cruise No. 31. Internal waves oc- 

 cur with amplitudes of the order of 25 feet but with periods poorly 

 defined. Visual examination suggests six-hour and two-hour periods 

 rather than those of twelve or sixteen hours. It is felt therefore that 

 these internal waves are not a determining influence on the G.E.K. 

 results, but that they possibly account for some of the aberrations and 

 short-period constituents. 



In Table III, the average residual current calculated from the three 

 time studies is compared with the dynamic topographies and with the 

 approximate drift of the ship as determined by deviations from the 

 courses run, measured by loran fixes. In Cruise No. 29, the G.E.K. com- 

 pares well with the drift of the ship but not with the dynamic topo- 

 graphies. This was in a period of light winds in which the ship might 

 be expected to move with the water. In Cruise No. 31, there is little 

 agreement, possibly because the winds averaged 20 knots from the north. 

 However, the direct current measurements compare favorably with the 

 dynamic topographies close to the seamount. Farther away, the velocity 

 and direction derived from the topographies are extremely uncertain 

 and are not shown. It seems well established therefore that the rotary 

 changes observed by the G.E.K. in deep water have their counterpart in 

 the direct measurements of currents. 



Conclusions and Summary 

 The water circulation off the coasts of Vancouver Island, Washing- 

 ton and Oregon in late spring and summer has been studied by means 

 of dynamic topographies and the G.E.K. A picture is presented which 



