Energetics of Wind-Induced Internal Wave Radiation from the Base of the Mixed Layer in the North Atlantic

Energy transfer mechanisms between atmosphere and the deep ocean have been studied for many years. Their importance to the ocean’s energy balance and possible implications on mixing are widely accepted. The slab model is a well-established simulation of near-inertial motion and energy inferred through wind-ocean interaction. However, temporally coarse resolution wind forcing data in combination with rough internal wave energy flux assumptions are mainly used.

A slab model using hourly wind forcing from the NCEP-CFSR reanalysis allowing computations up to high latitudes without loss of resonance was set up. It was validated with buoy data from 44 sites in the Atlantic, Indian and Pacific Oceans and the Mediterranean Sea. Augmenting the one-dimensional model by the horizontal divergence of the near-inertial current field at the mixed layer base led to direct estimates of energy transfer spectra of radiation of internal waves into the ocean interior. No crucial assumptions on transfer physics were made.

Results of the hybrid model indicated the presence of internal wave modes at the base of the mixed layer. Spatially-advancing wind stress fronts were identified as their main driver and thus they acted as the major source for internal wave radiation into the deep ocean. Accordingly, mid-latitude storms with a strong seasonal cycle as well as isolated tropical storm tracks are dominant in energy fluxes in the North Atlantic.