Coupling Current, Waves, and Wind Stress over the Gulf Stream

The exchanges of momentum, heat, moisture, and gas across the air-sea interface play crucial roles in atmospheric and oceanic circulations on variety of spatial and temporal scales. Therefore, improved understanding and realistic simulations of air-sea fluxes are critical to advancing oceanic and atmospheric prediction capabilities. This study provides the first detailed analysis of oceanic and atmospheric responses to the current-stress, wave-stress, and wave-current-stress interaction around the Gulf Stream using a high-resolution three-way coupled regional modeling system. In general, our results highlight the substantial impact of coupling currents and/or waves with wind stress on the air-sea fluxes and upwelling/downwelling in the upper ocean over the Gulf Stream. In the wave-current-stress coupled experiment, wind stress increases by 15% over the Gulf Stream. Alternating positive and negative bands of changes of Ekman-related vertical velocity appear in response to the changes of wind stress curl along the Gulf Stream, with magnitudes exceeding 0.3 m/day (95th percentile). This small-scale feature is also revealed by four-year averages of 25-km scatterometer observations. The response of wind stress and its curl to the wave-current-stress coupling is not a linear combination of responses to the wave-stress coupling and the current-stress coupling. Therefore, both waves and currents, and their interactions should be included in coupled models. Considerable changes of latent heat flux in excess of 20 W/m2 and sensible heat flux in excess of 5 W/m2 are found over the Gulf Stream in all coupled experiments. Sensitivity test shows that SST-induced difference of air-sea humidity is the major contributor to the LHF change.