Fluid Exchange across a Meandering Jet

TLDR

The study is motivated by recent float trajectory analyses in the Gulf Stream. Fluid parcel motion in a two‑dimensional kinematic meandering jet model is analyzed with Melnikov's method. The study finds that cross‑jet exchange efficiency depends on fluctuation frequency—high frequencies favor core‑trapped fluid exchange, low frequencies favor trapped‑surrounding fluid exchange—while propagating waves with matching phase speeds enhance regime exchange, and overall exchange across the jet core is less efficient than between adjacent regimes, preserving core gradients.

Abstract

The motion of fluid parcels in a two-dimensional kinematic model of a meandering jet is investigated using Melnikov's method. The study is motivated by a recent analysis of float trajectories in the Gulf Stream. The results indicate that the efficiency of cross-jet exchange induced by fluctuating meander amplitudes depends strongly on the frequency of the fluctuations. For high frequencies (≳0.04 cpd), exchange between the core of the jet and regions of "trapped" fluid moving with the meander is preferred, while for low frequencies (≲0.04 cpd), exchange between the "trapped" fluid and the slow-moving fluid surrounding the jet is preferred. Propagating waves superimposed on the meandering jet can efficiently cause exchange between regimes when their phase speeds roughly match the basic flow velocities along the regime boundaries. Numerical results suggest that exchange across the center of the jet is less efficient than exchange between adjacent regimes so that the meandering jet will tend to stir fluid along each of its sides but preserve gradients across the jet core.