The circulation systems of Bikini and Rongelap lagoons

Abstract

Four and one‐half months of the early part of 1946 were spent in the field at Bikini and Rongelap Atolls to study the circulation systems within the lagoons. Additional synoptic studies were made in the laboratory of kinematically similar models based on early field data. The results of these studies were later tested against further observations made in the field. It was found that both lagoons exhibited a primary circulation (overturning wind‐driven circulation) and a secondary circulation (rotary circulation composed of two counter‐rotating compartments). The direction of the primary circulation and the division between the counter‐rotating compartments of the secondary circulation were always contained in a vertical plane having roughly the azimuth of the prevailing wind. The vigor of both circulations varied with the average wind strength taken over the previous 24 hours. Perturbations of the primary and secondary modes of circulation were produced by tides, waves, and the North Equatorial Current which surrounds the atolls of the northern Marshall Islands group. Seasonal changes were also noted; the circulation of the winter months when the northeast trade‐winds prevail showed a marked stability and strength which was lacking in the summer season when the atolls are on the edge of the belt of doldrums.In addition to the qualitative synopsis of the circulations, numerical data are presented in tabular form which show the volumetric exchanges of water between the lagoons and the ocean. An estimate is made of the rates of refreshment and overturning of each lagoon. A chart of the values of eddy diffusion in the surface plane is given for Bikini, as well as secondary data on the behavior of current poles and dye trails in a variety of wind and current strengths.