Impact of wind stress formulation on Gulf Stream pathway and variability

Eric P. Chassignet^*Xiaobiao Xu

• Center for Ocean-Atmospheric Studies, Florida State University, Tallahassee, United States

Current feedback affects surface motions and the numerical experiments presented in this paper highlight its importance when modeling the Gulf Stream. This is not a new notion, but its implementation in the high-resolution 1/50⁰ North and Equatorial Atlantic HYCOM model configuration of Chassignet et al. (2023) not only allows us to quantify its impact on the Gulf Stream pathway and variability via detailed comparisons to in-situ and altimetry data, but also to evaluate the latest mean dynamic topography derived from combining altimeter and satellite gravity data, drifters, and hydrological profiles. Introduction of the current feedback induces an "eddy-killing" effect that can reduce the level of eddy kinetic energy (EKE) in the model by as much as 30%, but this drop in EKE can also be compensated by decreasing the model's explicit viscosity accordingly. The current feedback is most effective at damping energy at scales above 50-60 km while the reduction in explicit viscosity leads to an increase in small-scale energy. Addition of the current feedback also does result in a much more realistic distribution of the sea surface height variability and the resulting mean field. The detailed comparison of the model results to altimeter data and in-situ measurements leads us to state that the latest mean dynamic topography from CNES-CLS underestimates the maximum Gulf Stream velocity by approximately 10% and that the representation of the shelf circulation may be underestimated.