Role of Eddies in the Maintenance of Multiple Jets Embedded in Eastward and Westward Baroclinic Shears

Abstract

Multiple zonal jets observed in many parts of the global ocean are often embedded in large-scale eastward and westward vertically sheared background flows. Properties of the jets and ambient eddies, as well as their dynamic interactions, are found to be different between eastward and westward shears. However, the impact of these differences on overall eddy dynamics remains poorly understood and is the main subject of this study. The roles of eddy relative vorticity and buoyancy fluxes in the maintenance of oceanic zonal jets are studied in a two-layer quasigeostrophic model. Both eastward and westward uniform, zonal vertically sheared cases are considered in the study. It is shown that, despite the differences in eddy structure and local characteristics, the fundamental dynamics are essentially the same in both cases: the relative-vorticity fluxes force the jets in the entire fluid column, and the eddy-buoyancy fluxes transfer momentum from the top to the bottom layer, where it is balanced by bottom friction. It is also observed that the jets gain more energy via Reynolds stress work in the layer having a positive gradient in the background potential vorticity, and this is qualitatively explained by a simple reasoning based on Rossby wave group velocity.

Tilted drifting jets over a zonally sloped topography: effects of vanishing eddy viscosity

“…Oceanic jets are dynamically similar to the zonal jets seen on planetary atmospheres of Jupiter and Saturn, which are formed due to interactions between Rossby waves and turbulent mesoscale eddies (Rhines 1975(Rhines , 1994Galperin et al 2006;Dritschel & McIntyre 2008). Mesoscale eddies, which gain energy through baroclinic instability, are responsible for forcing the zonal jets via local or non-local upscale energy transfer (Rhines 1975;Thompson & Young 2007;Berloff, Kamenkovich & Pedlosky 2009b;Berloff & Kamenkovich 2013a,b;Khatri & Berloff 2018b). However, there are some notable differences between atmospheric and oceanic multiple jets.…”

“…2006; Dritschel & McIntyre 2008). Mesoscale eddies, which gain energy through baroclinic instability, are responsible for forcing the zonal jets via local or non-local upscale energy transfer (Rhines 1975; Thompson & Young 2007; Berloff, Kamenkovich & Pedlosky 2009 b ; Berloff & Kamenkovich 2013 a , b ; Khatri & Berloff 2018 b ). However, there are some notable differences between atmospheric and oceanic multiple jets.…”