Oceanic eddies accompanied by a significant vertical velocity are known to be of great importance for the vertical transport of various climatically, biologically or biogeochemically relevant properties. By applying quasi-geostrophic w theory, we extend the classic “beta-spiral” model, traditionally used for gyre circulations, to isolated and nearly symmetric oceanic mesoscale eddies. We propose that the vertical motion within these eddies is characterized by a pronounced east-west dipole pattern, with deep oceanic penetration. Numerical simulations of idealized isolated eddies coupled with diagnostics from the w-equation confirm that this w-dipole is dominated by the “eddy beta-spiral” mechanism in the beta-plane simulation, while the w-dipole disappears in the f-plane simulation as expected. Analyses of relatively isolated warm and cold eddy examples show good agreement with the proposed mechanism， indicating that beta-term should not be ignored in the w-equation. These findings improve our understanding of eddy vertical motions and suggest that this w-dipole may significantly influence the vertical mixing and transport of deep seawater, inspiring further research.
 

Mesoscale eddies, Vertical velocity, β effect, ω equation, Dipole patterns