Eddies In Hawaiian Waters

Oceanographic observations near the Hawaiian Islands demonstrate that ocean circulation is extremely variable and is dominated by eddies with diameters ranging from 50 to 150 kilometers. The data from 20 cruises that describe these eddies have been analyzed. Most of the eddies are cyclonic, and have been observed during all seasons. Observations show that the flow in them is nearly geostrophic and volume transports can be as large as 8 million cu m/sec. Although surface flow around them can be in excess of 100 cm/sec, the eddies are relatively shallow in depth and most of the horizontal flow is concentrated in the upper 150 m, above the 20C isothermal surface. Calculations show that the eddies are not generated by the large-scale flow through the Hawaiian Islands--in the sense of a Karman vortex stream behind an obstacle. Energy calculations indicate rather that the eddies are driven by strong, local winds blowing through the restricted passage between the islands of Maui and Hawaii. The calculations show that the eddies have a formation time of between 2 and 6 weeks, a value consistent with observations. (Author).