The concept of Available Potential Energy (APE) has become a powerful diagnostic in ocean energetics. However, our current understanding of APE in the mixed layer remains limited for two reasons. First, the classical Lorenz APE framework is based on the adiabatic parcel rearrangement in the entire domain of interest, and thus is inappropriate for diagnostics of mesoscale and submesoscale processes which are generally associated with local parcel rearrangement around these processes. Second, the widely used quasi-geostrophic (QG) approximation of APE relies on the small perturbation assumption, which is not applicable for processes with large perturbations, such as submesoscale eddies and filaments in the mixed layer. To this end, we employ a general localized finite-amplitude APE framework to evaluate the spatio-temporal characteristics of APE in the global mixed layer. We further constrain the horizontal scale of the parcel rearrangement based on the length‐scale of interest, and carry out a scale-dependent APE analysis. The more accurate APE may provide insights into the parameterizations of mesoscale and submesoscale eddies in climate models.
 

available potential energy; scale-dependent adiabatic rearrangement, mixed layer