ENSO Effects on Gulf of Alaska Eddies

Abstract

Generation and propagation of eddies in the coastal regions of the eastern Gulf of Alaska are examined based on ouput from a numerical ocean model. Results from a 1/8° six-layer isopycnal, wind-forced Pacific basin model are examined within the Gulf of Alaska during the 14-yr period starting in January 1981. Interannual variability in the upper ocean coastal circulation in the Gulf of Alaska is linked to the El Niño?Southern Oscillation phenomenon in the tropical Pacific Ocean, via coastal Kelvin waves and atmospheric teleconnections. El Niño events destabilize the Alaska Current by enhancement of the velocity shear in the vertical. The instability ultimately results in the formation of multiple strong anticyclonic eddies along the coast, which slowly propagate into the Gulf of Alaska where they can survive for more than 1 yr. A typical value for the diameters of the anticyclonic eddies is 200 km in the data and in the model. These eddies are strongly baroclinic, with a typical value for the velocity differences between layers 1 and 2 of 15 cm s?1. El Viejo (La Niña) events generally reduce eddy formation.