Surface wave effects in the NEMO ocean model

Surface waves affect the ocean mixed layer through at least three distinct mechanisms: (i) The Coriolis-Stokes effect which adds a forcing term to the momentum equations proportional to the Stokes drift velocity. (ii) The water-side stress differs from the air-side stress because momentum is absorbed by growing waves and injected into the ocean when waves break. (iii) Breaking waves modify the level of turbulent kinetic energy (TKE) in the wave-affected upper layer of the ocean mixed layer, thus changing the mixing. Here we present experiments with NEMO forced with fluxes of momentum and TKE computed from the WAM wave model (archived with the ERA-Interim reanalysis). We also show some early results from coupled experiments where NEMO is coupled to the Integrated Forecast System (IFS) of ECMWF. The momentum flux (stress) and the Coriolis-Stokes forcing change the sea surface temperature by about 0.5 K. The modified TKE has a much greater impact with differences in excess of 2 K in the summer hemisphere. Since November 2013 (Cycle 40R1) the Integrated Forecast System (IFS) of ECMWF has had a one-degree NEMO model coupled to the atmosphere from day 0 with TKE fluxes and Coriolis-Stokes forcing from the WAM model.