On forcing ocean models with scatterometer-derived winds

Scatterometer-derived estimates of the air-sea momentum flux show a clear signature of ocean surface currents. Simple theory suggests that the stress magnitude is anticorrelated with the alignment of the surface currents and winds and numerical simulations show this to lead to a substantial reduction in the wind power source. Because model currents will necessarily differ from observed currents, however, these anticorrelations need not persist in situations where a scatterometer-derived wind stress field is used to force realistic ocean circulation models. To make this point more explicit, we consider a twin experiment in the classic double gyre setting. The run corresponding to ``truth" is forced with a surface-ocean-velocity-dependent stress and this same stress is used to drive a second experiment in which the initial conditions have been perturbed. Differences between the two are analysed in terms of model energetics.