The effects of ocean surface waves on global intraseasonal prediction: case studies with a coupled CFSv2.0–WW3 system

Abstract

This article describes the implementation of a coupling between a global forecast model (CFSv2.0) and a wave model (WW3) and investigates the effects of ocean surface waves on the air–sea interface in the new framework. Several major wave-related processes, including the Langmuir mixing, the Stokes–Coriolis force with entrainment, air–sea fluxes modified by the Stokes drift, and momentum roughness length, are evaluated in two groups of 56 d experiments, one for boreal winter and the other for boreal summer. Comparisons are made against in situ buoys, satellite measurements, and reanalysis data to evaluate the influence of waves on intraseasonal prediction of sea surface temperature (SST), 2 m air temperature (T02), mixed layer depth (MLD), 10 m wind speed (WSP10), and significant wave height (SWH). The wave-coupled experiments show that overestimated SSTs and T02s, as well as underestimated MLDs at mid-to-high latitudes in summer from original CFSv2.0, are significantly improved due to enhanced vertical mixing generated by the Stokes drift. For WSP10s and SWHs, the wave-related processes generally reduce biases in regions where WSP10s and SWHs are overestimated. On the one hand, the decreased SSTs stabilize the marine atmospheric boundary layer and weaken WSP10s and then SWHs. On the other hand, the increased roughness length due to waves reduces the originally overestimated WSP10s and SWHs. In addition, the effects of the Stokes drift and current on air–sea fluxes also rectify WSP10s and SWHs. These cases are helpful for the future development of the two-way CFSv2.0–wave coupled system.