R ESTRICTED 



5 



2,2 Oceanography and meteorology 



2,21 The current system of the region 



Bikini Atoll lies in the North Equatorial Current , a v/es- 

 terly drift of v/ater largely wind-driven by the 1^ Trades. The 

 surface water flow is about half a Icnot. The velocity decreases 

 with depth, but slight flov/ can be detected at depths of 200 fm. 

 or more. The southerly limit of the ciirrent is believed to lie 

 between 6° and 9^1 at this longitude, but the available data are 

 meager. It seems likely that the seasonal shift of the Trades and 

 the North Equatorial Current is never large enough to place Bi- 

 kini in the DoldrTim Belt; hov/ever, it is iLientioned in passing 

 that if this should happen, the conclusions in this report about 

 the current system inside and outside the lagoon would be invalid 

 for the period in question. 



The simple picture of a v/esterly current is modified and 

 complicated by the presence of the atoll. Only the upper few 

 feet of water can flow unimpeded into the lagoon. The reuiain- 

 der splits and passes around the obstruction, giving rise to eddies 

 and to variations in the direction of flow which extend some dis- 

 tance arourid the atoll. These currents v/ill be described in 

 more detail in a subsequent report. 



The temperature of the surface water is about 80° to 82°F. 

 There is a virtually mixed layer of water in the upper 300 to 

 400 feet, in which the decrease in temperature with depth is at 

 most 2^. Thus the water that enters the lagoon is relatively 

 homogeneous. Erom the surface to the depth of the deepest sill, 

 no observation has been obtained of a variation of as much as 1°. 



A tide station was operated inside the lagoon off Bikini 

 island at latitude 11^37 'N, longitude 165031'E, and another on 

 the seaward side of the sand spit north of the island. The ob- 

 served times of high and low water agreed with the predicted 

 tides for Bikini (USCGS) within the limits of accuracy of the 

 equipment. The observed tidal range averaged 87% of the pre- 

 dicted range. Lowest low v>rater corresponded to a reading of 1.19 

 feet on the tide staff. The station is believed to be representa- 

 tive of conditions over the entire lagoon for the following rea- 

 sons: (a) The size of the channels permits easy communication 

 vyrith the ocean, (b) No appreciable tidal lag has been found be- 

 tween observations inside and outside the reef. (c) Winds are 

 steady and storm tides \mlikely. 



The large Pacific tidal v/ave that caused extensive damage 

 in Alaska and Hav/aii on 2 April was recorded at Bikini at 1530 

 as a single v/ave raising the v/ater level one and a half feet 



