62 



ATKINSON 



NE 

 TRADES 



//^/// 



Fig. 4 Lagoon surface currents from drogue data. Arrows represent smoothed drogue tra- 

 jectories over varying lengths of time; they arc not vectors. Some drogue runs were made 

 during calm or variable wind. [From Atkinson et al. with permission.] 



tion of the previous 6 to 12 hours. Drogue paths over 6 

 hours showed no rapid changes in directions; however, 

 they often traced slight curves, suggesting they were 

 slowly changing direction with the wind. 



The speed of the surface current is approximately 2% 

 of the wind speed (Fig. 5). Data for Fig. 5 were taken 

 from days when both the average wind direction and the 

 average wind speed had small standard deviations. Correla- 

 tions between wind and current speed and wind and 

 current direction for all data are poor, probably because 

 cross-reef currents and tidal channel currents influence the 

 surface current at least 5 km into the lagoon. 



The surface current moves in a layer which varies from 

 5 to 15 m thick. The average thickness of the surface 

 layer is approximately 10 m. Downwind volume transport 

 of the surface layer is approximately 9.2 X 10 m per 

 tidal cycle (Table 2). Von Arx (1948) reported that the sur- 

 face current at Bikini is 5 to 20 m thick and changed 

 depending on the wind conditions. 



The mid-depth current lies between 10 and 30 m in 

 depth This current generally flows northeastward, oppo- 



20 



Current = 0.0246 -^ 2.06 (Wind) 

 r2 = 0.96 



_L- 



-o 



_1_ 



1 2 3 4 5 6 7 



Wind speed (m s-i) 

 Fig. 5 Surface current speed as a function of wind speed for 

 the center of the lagoon. 



