Online isolation of near-inertial internal waves in ocean general circulation models

Near-inertial internal waves (NIWs) play an important role in furnishing ocean diapycnal mixing. However, parameterization of NIW-induced mixing in high-resolution ocean general circulation models (OGCMs) remains a challenging problem partially due to the lack of appropriate tools for isolating NIWs during the model integration. In this study, we propose two new methods feasible for online isolation of NIWs in high-resolution OGCMs, i.e., the two-step filter and three-step filter. The two-step filter only requires the velocity records to be stored at two time steps. It performs reasonably well in isolating NIWs poleward of 30 degrees if the time step is set as 6 h. By utilizing the velocity information at one additional time step, the three-step filter with a time step of 6 h generally outperforms the two-step filter in the global ocean. Specifically, the three-step filter results in reasonable isolation of NIWs poleward of 15 degrees where the NIW-induced mixing is strongest.