Mesoscale eddies northeast of the Hawaiian archipelago from satellite altimeter observations

Abstract

Enhanced mesoscale eddy activity northeast of the Hawaiian archipelago was investigated by using the high‐pass filtered satellite altimetric sea surface height (SSH) data of the past 16 years. The level of eddy kinetic energy (EKE) shows significant interannual variations, which appear well correlated to the large‐scale atmospheric wind forcing associated with the Pacific Decadal Oscillation index; the EKE levels in the area along the Subtropical Front zone in 1997–1998 and 2003–2005, for example, were three times as large as those in the low EKE years. Spectral analyses in the 3° latitude by 5° longitude subregions revealed the dominant mesoscale periods ranging from 90 days near 18°N to 180 days near 36°N. A 3‐layer quasi‐geostrophic model constrained by World Ocean Atlas 2005 climatologies was used to explore instability of the regional circulation. The analysis shows a geographical match between baroclinic instability strength and the observed RMS SSH variability and a temporal match between seasonally varying instability strength and the observed seasonal EKE modulation, and suggests that baroclinic instability by the vertically sheared, regional mean circulation provides the energy source for the enhanced eddy variability northeast of the Hawaiian archipelago.