Ocean current and wave effects on wind stress drag coefficient over the global ocean

The effects of ocean surface currents and dominant waves on the wind stress drag coefficient (C-D) are examined over the global ocean. Major findings are as follows: (1) the combination of both ocean wave and current speeds can result in reductions in daily C-D (>10%), but the notable impact of the latter is only evident in the tropical Pacific Ocean; (2) the presence of waves generally makes winds weaker and C-D lower almost everywhere over the global ocean; (3) strong ocean currents near the western boundaries (Kuroshio and Gulf Stream) do not substantially influence C-D since the winds and currents are not always aligned; and (4) the change in speed used in bulk flux parameterization also causes large changes in fluxes. Globally, the combined outcome of ocean currents and waves is to reduce C-D by about (2%), but spatial variations (0% to 14%) do exist.