Asymmetries in Anticyclone Catalyze Submesoscale Motions

Abstract Oceanic mesoscale eddies are often asymmetric, exhibiting horizontal deformation and vertical tilt, yet the implications of these structural asymmetries for finer‐scale dynamics remain poorly understood. Based on a series of high‐resolution numerical experiments, we found that asymmetric anticyclones act as potent catalysts for submesoscale motions compared to symmetric counterparts. This catalysis follows a clear dynamical pathway. Initial asymmetries in elliptical and vertically tilting anticyclones rapidly develop vortex Rossby waves (VRWs) of azimuthal wavenumber‐2 and wavenumber‐1, respectively, through axisymmetrization. The breakdown of these VRWs generates small‐scale filaments, fronts and vortices along the periphery of the anticyclone, accompanied by strong strain and frontogenesis. Submesoscale instabilities, including mixed barotropical/baroclinic and symmetric instability then appear, driving vigorous submesoscale motions. Frontogenetic tendency analysis reveals that this frontogenesis is primarily driven by two ageostrophic processes, horizontal advection and vertical straining. Our findings elucidate a potential mechanism in idealized simulations whereby mesoscale eddy asymmetries catalyze submesoscale motions.