| Popis: |
The role of the wind-driven ocean gyres in the midlatitude climate variability is investigated using an idealised, eddy-resolving, quasigeostrophic, coupled model. The model consists of a double gyre box ocean and a periodic channel atmosphere which are coupled together by mixed layers that allow for transfers of heat and momentum. The entire model is driven by fixed, latitudinally-varying solar radiation that is redistributed by a linearised radiation scheme. Our findings reveal a coupled interaction that involves a positive feedback between meridional shifts of the ocean eastward jet extension and downstream displacements of the atmospheric westerly jet. The displacement of the atmospheric jet is resolution-dependent and caused by shifts in the latitudinal centre of low-level baroclinicity, while meridional shifts of the ocean eastward jet are likely controlled by the propagation of baroclinic Rossby waves that form in the eastern basin. Effects of mesoscale turbulence and intrinsic variability of the ocean jet disrupts the arrival of Rossby waves at the western boundary and thus reduces its predictability. In addition, the ocean gyre response is shown to be dependent on forcing location, and a dynamically-distinct, inertial recirculation zone response is found for western basin wind-curl anomalies. Other relevant nonlinear dynamics that maintain the wind-driven ocean gyre circulation are investigated using an adiabatic, fixed-wind, double gyre box ocean model. It is revealed that nonlinear restructuring of the western boundary layer inhibits viscous relative vorticity fluxes, creating an accumulation of enstrophy in the gyres. This enstrophy is advected downstream into the inertial recirculation zones which in turn supports the eastward jet. The growing imbalance in enstrophy is then eventually rectified by inter-gyre potential vorticity fluxes. Open Access |
