Cross-frontal mixing in a meandering jet

Abstract

A Gulf Stream-like meandering current is kinematically modeled using a given streamfunction. Under suitable parameter values a "front' exists along the velocity maximum across which there is no transport, but with mixing occurring on either side. An analogous barrier exists in the Gulf Stream but appears to fade with depth. The conditions for mixing across the model front are studied using the Chirikov overlap criterion, which indicates the front breaks down for meander amplitude above a critical threshold that is inversely dependent on the ratio of meander phase speed and current speed. It is suggested that the increase in cross-frontal mixing in the deeper levels of the Gulf Stream is the result of current meandering and the decrease of current velocity with depth. The mechanism for this is interaction of different meander modes traveling along the Gulf Stream. These ideas are shown to be consistent with field measurements of tracers in the ocean. -Author