On the β-Induced Coastal Trapping of a Baroclinic Eddy

Abstract

A recurring mesoscale (diameter 100?150 km) baroclinic anticyclonic eddy lies proximate to the shelf break of the southeastern coast of the North Island of New Zealand new Cook Strait. Its appearance and persistence is interpreted in terms of a trapping mechanism suggested by Nof, which consists of an eddy-integrated dynamical balance formed between the ?-induced equatorward force and a poleward directed pressure gradient attributed to an opposing southward flowing barotropic coastal current. For parameter values typical of the eddy, calculations show that alongshore coastal flows within the East Cape Current in the range of 2?10 cm s?1 would be sufficient to arrest and trap the eddy.