Wind-generated eddy characteristics in the lee of the island of Hawaii

Weekly satellite sea surface height (SSH) anomaly data are used to clarify the mesoscale eddy characteristics in the lee of the island of Hawaii, the largest island in the Hawaiian Island chain. The lee eddy variability can be separated into two geographical regions. In the immediate lee southwest of Hawaii (Region E), eddy signals have a predominant 60 day period and a short life-span, whereas in the region along 19 degrees N west of similar to 160 degrees W (Region W), the eddy variability is dominated by 100 day signals and extends over a broad region. By applying a linear Ekman pumping model forced by the weekly QuikSCAT wind data, we find that the observed 60 day eddy signals originate in the southwest corner of Hawaii and are induced by the local 60 day wind stress curl variability associated with the blocking of the trade wind by the island of Hawaii. The relationship between the wind forcing and the observed SSH signals demonstrates the role of the ocean as an integrator that responds more effectively to the low-frequency synoptic atmospheric forcing (similar to 60 days) than to the higher-frequency forcing (similar to 30 days). Since the large-amplitude 60 day SSH anomalies take 1-2 weeks to fully develop, it is possible that real-time observed wind stress data can be used for the prediction of these anomalies. In contrast to the wind-induced 60 day eddy signals in the lee of the island of Hawaii, the 100 day eddy signals in Region W are likely generated by the instability of the sheared North Equatorial Current and Hawaii Lee Countercurrent.