Instability Dynamics of a Subtropical Jet and Applications to the Azores Front Current System: Eddy-Driven Mean Flow

Abstract

Abstract The Azores front is associated with an eastward flowing subtropical jet, which coincides with the northern edge of the North Atlantic subtropical gyre and forms a southern branch of the Gulf Stream. An intensive study of the eddy-driven mean flow induced by the nonlinear instability of the jet has been conducted. Using a primitive equation numerical model initialized with the summer hydrological fields typical of the Azores front, the authors show that the mesoscale patterns that appear after a few months are largely determined by baroclinic instability processes. the jet and its associated mesoscale turbulence have a strong meridional asymmetry due to the strongly sloping thermocline. In general, an anticyclonic meander, which grows and deforms northwestward, generates a pinched-off anticyclone while a cyclonic meander, which grows and deforms southwestward, degenerates in a thin filamental structure that will dissipate before any cyclone can be pinched off. The authors propose a mechanism that ...