Formation and maintenance of zonally-elongated transients in the ocean.
Formation and maintenance of zonally-elongated transients in the ocean.
Abstract:
Anisotropic, zonally-elongated flow structures are present in every oceanic basin. Altimetry-based estimates demonstrate that such patterns are often non-stationary and do not span the entire zonal width of ocean basins. Modelling results further suggest the key role of these zonally-elongated, large-scale transients (ZELTs) in setting zonal predominance of the material transport. The mechanisms of ZELTs formation, their spatial and time scales and their role in ocean energetics remain unclear.
We use a two-layer, quasi-geostrophic model forced by uniform baroclinic shear to study dynamics and energetics of ZELTs. Several runs have been performed to test the sensitivity of the structure and magnitude of ZELTs to (with respect to) bottom drag coefficient. Increase in the bottom drag leads to the enlargement of the meridional length scale and attenuation of the magnitude. We demonstrate that the dynamics of ZELTs are governed by transient non-linear forcing produced by the interactions between eddies (E-E-E) and the scattering of eddies over the mean state (E-M-E). The experiments with the intermediate value of bottom friction suggest that neglecting E-M-E forcing results in considerable weakening of ZELTs and their disappearance when E-E-E forcing is removed. In contrast, large bottom friction simulations without E-M-E forcing show almost identical ZELTs structure and magnitude compared to the full simulation; if E-E-E forcing is removed, ZELTs structure is unchanged, but their magnitudes twice weaken.
We use a two-layer, quasi-geostrophic model forced by uniform baroclinic shear to study dynamics and energetics of ZELTs. Several runs have been performed to test the sensitivity of the structure and magnitude of ZELTs to (with respect to) bottom drag coefficient. Increase in the bottom drag leads to the enlargement of the meridional length scale and attenuation of the magnitude. We demonstrate that the dynamics of ZELTs are governed by transient non-linear forcing produced by the interactions between eddies (E-E-E) and the scattering of eddies over the mean state (E-M-E). The experiments with the intermediate value of bottom friction suggest that neglecting E-M-E forcing results in considerable weakening of ZELTs and their disappearance when E-E-E forcing is removed. In contrast, large bottom friction simulations without E-M-E forcing show almost identical ZELTs structure and magnitude compared to the full simulation; if E-E-E forcing is removed, ZELTs structure is unchanged, but their magnitudes twice weaken.