Energy Flux Into Near-Inertial Internal Waves Below The Surface Boundary Layer In The Global Ocean

Near-inertial internal waves (NIWs) are thought to play an important role in powering the turbulent diapycnal mixing in the ocean interior. Nevertheless, the energy flux into NIWs below the surface boundary layer (SBL) in the global ocean is still poorly understood. This key problem is addressed in this study based on a Community Earth System Model (CESM) simulation with a horizontal resolution of similar to 0.1 degrees for its oceanic component and similar to 0.25 degrees for its atmospheric component. The CESM shows good skill in simulating NIWs globally, reproducing the observed magnitude and spatial pattern of surface NIW currents and wind power on NIWs (W-I). The simulated downward flux of NIW energy (F-SBL) at the SBL base is positive everywhere. Its quasi-global integral (excluding the region within 5 degrees S-5 degrees N) is 0.13 TW, about one-third the value of W-I. The ratio of local F-SBL to W-I varies substantially over the space. It exhibits an increasing trend with the enstrophy of balanced motions (BMs) and a decreasing trend with W-I. The kinetic energy transfer from model-resolved BMs to NIWs is positive from the SBL base to 600 m but becomes negative farther downward. The quasi-global integral of energy transfer below the SBL base is two orders of magnitude smaller than that of F-SBL, suggesting the resolved BMs in the CESM simulations making negligible contributions to power NIWs in the ocean interior.