The Effects of Ocean Surface Waves on Global Forecast in CFS Modeling System v2.0

Abstract. It has been well known that ocean surface gravity waves have enormous effects on physical processes at the atmosphere–ocean interface. However, the effects of surface waves on global forecast in several days are less studied. To investigate this, we incorporated the WAVEWATCH III model into the Climate Forecast System Model version 2.0 (CFS2.0), with the Chinese Community Coupler version 2.0 (C-Coupler2). Two major wave-related processes, the Langmuir mixing and the sea surface momentum roughness, were considered. Extensive comparisons were performed against in-situ buoys, satellite measurements and reanalysis data, to evaluate the influence of the two processes on the forecast of sea surface temperature, mixed layer depth, significant wave height, and 10-m wind speed. A series of 7-day simulations demonstrate that the newly developed atmosphere-ocean-wave coupling system could improve the CFS global forecast. The Langmuir mixing parameterization could increase the vertical movement of water and effectively reduce the warm bias of sea surface temperature and shallow bias of mixed layer depth in the Antarctic circumpolar current in austral summer, whereas the significant wave height and 10-m wind speed are insensitive to it. On the other hand, the modified momentum roughness length could significantly reduce the overestimated 10-m wind speed and significant wave height in mid-high latitudes. This is because the enhanced frictional dissipation at high wind speed could reduce 10-m wind speed and consequently decrease the significant wave height. But its effect on the temperature structure in upper ocean is less obvious.