In this study we investigate the role of stratification in the formation and persistence of eastward jets (like the Gulf Stream and Kuroshio currents). Using a wind-driven, two-layer quasi-geostrophic model in a double-gyre configuration, we construct a phase diagram to classify flow regimes. The parameter space is defined by a criticality parameter ξ, which controls the emergence of baroclinic instability, and the ratio of layer depths δ, which describes the surface intensification of stratification. Eastward jets detaching from the western boundary are observed when δ≪1 and ξ∼1, representing a regime transition from a vortex-dominated western boundary current to a zonostrophic regime characterized by multiple eastward jets. The emergence of the coherent eastward jet is further addressed with complementary 1.5-layer simulations and explained through both linear stability analysis and turbulence phenomenology. Lastly, we briefly assess the relevance of the quasi-geostrophic model by altering the stratification of a hydrodynamic shallow-water model of the North Atlantic, and comment on observed changes in the behavior of the eastward jet.

Lieu
LOCEAN-IPSL, couloir 45-55, 4^e étage, pièce 417

Visio
https://ird-fr.zoom.us/j/91940354222?pwd=aXD6AtUxDsmmbIOua7MP9NSrCfBc14.1