Vortex waves and vertical motion in a mesoscale cyclonic eddy

Oceanic eddies are coherent mesoscale features present anywhere in the World Ocean. The vertical motion associated with eddies plays a fundamental role in the ocean circulation and ocean-atmosphere interaction. Eddies also transport phytoplankton and modify the nutrient fluxes from the deep layers into the euphotic zone, affecting open ocean primary production and potentially influencing the global carbon cycle. However, vertical exchanges driven by mesoscale eddies cannot be directly measured. Here, the evolution of a mesoscale cyclonic eddy is described through combined satellite-in situ observations and inviscid, adiabatic semigeostrophic diagnostic equations. The synthetic estimates show that vortex azimuthal oscillations dominate the vertical velocity field in the eddy interior. These oscillations are compatible with the propagation of potential vorticity (PV) disturbances on the radial gradient of the PV associated with the basic-state eddy, known in literature as vortex Rossby waves. Vortex waves have been widely analyzed in theoretical studies, laboratory experiments, and numerical models, but rarely measured directly in the oceans. Their role in the vertical exchange and Lagrangian particle displacement is investigated here for the first time directly from ocean observational data. These results further demonstrate that conventional eddy pumping models fail to correctly describe the vertical velocity field and open a new perspective on the characterization of mesoscale dynamics through combined measurements and more advanced dynamical approximations.