On the sensitivity of the Drake Passage transport to air-sea momentum flux

An eddy-permitting state estimate and its adjoint are used to estimate the influence of wind stress perturbations on the time-mean transport through Drake Passage. The time-scale of influence of wind stress perturbations is order 100 days. Regarding spatial scales, the sensitivity of transport to wind stress is relatively smooth in regions of flat topography. In boundary regions and regions with complex topography, however, the sensitivity is enhanced and characterized by shorter length-scales of order 100 km. Positive perturbations to the zonal wind stress usually increase the Antarctic Circumpolar Current system (ACC) transport, though the wind stress curl is of primary influence where the currents are steered by topography. The results suggest that the ACC transport, with its complicated dynamics and path, cannot be determined solely by large-scale indices. By highlighting locations where the ACC is especially responsive to air-sea momentum fluxes we show where an accurate determination of atmospheric winds may best enhance ocean modeling efforts