Balanced to Unbalanced Motions at a Submesoscale Front and Energy Transfer From Eddy Splitting

Abstract

Submesoscale dynamics play a crucial role in energy redistribution in the upper ocean but remain challenging to observe due to their small spatial and temporal scales. We use ship-based observations of an oceanic submesoscale front sampled at high resolution while repeatedly traversed to observe deformation and splitting of an embedded cyclonic eddy. The velocity field from a shipboard acoustic Doppler current profiler was analyzed with spectral Helmholtz techniques and structure functions to examine the partitioning of kinetic energy into rotational and divergent components and energy transfer between mesoscales and submesoscales. During the eddy splitting, intensified mesoscale strain enhances the divergent component of kinetic energy in the mixed layer, where Rossby numbers are (Formula presented.). This coincides with a transient forward energy cascade from mesoscales to submesoscales. The wave-vortex decomposition reveals enhanced wave-like energy during and after splitting, with subsurface maxima indicative of near-inertial wave activity and downward energy propagation.