Trajectories of Mesoscale Eddies in Northwestern Region of the Hawaiian Islands Derived from Sea Surface Height Altimetry Data

Abstract

The structures of warm-core eddies and cold-core eddies were studied in the Northwestern region of the Hawaiian Islands. The study area extends from 180 ˚ W to 140 ˚ W in the zonal band 21˚N to 35˚ N. The variability of the sea surface height (SSH) was derived from the combined mission of TOPEX/Poseidon and ERS altimeters during the period between October 1992 and January 2004 and used to visualize the natures of several eddies generated in this region. Warm-core and coldcore eddies have been traced on maps with the altimeter observations every seven days. Emphasis was placed on the investigation of the spatial and temporal contexts for warm-core and cold-core eddies. It was found that both the warm and cold-core eddies propagated westward in the study area, and the propagation speed has been estimated as 3.25 cm/s. It was also discovered that the warm-core and cold-core eddies were generated by the baroclinic instability in the Subtropical Frontal Zone (STFZ), which is located at 28˚ to 30˚N, and that most of the eddies were observed to disappear along the islands. Eddies were affected by bottom topography in the vicinity of Hawaiian Ridge. In particular, the sea floor shallower than the depth of 1000 meters blocked mesoscale eddies. Finally, the Eddy Kinetic Energy (EKE), horizontal temperature distribution within warm-core eddy and cold-core eddy, and the relationship between eddy propagation speed and latitude were all investigated.