Estimation of Eddy Viscosity Profile in the Bottom Ekman Boundary Layer

Abstract

AbstractPrevious studies have shown that strong tidal currents can cause intense turbulent mixing near the seafloor in continental shelf areas. To quantify the turbulent mixing, the eddy viscosity coefficient is generally used. In this study, an estimation scheme is proposed to evaluate the eddy viscosity profile (EVP) in the bottom Ekman boundary layer based on the adjoint method. The estimation scheme is composed of the bottom Ekman boundary layer model and its adjoint model, and a minimization algorithm. The feasibility and effectiveness of the proposed scheme are validated by a series of twin experiments, where the proposed scheme is compared with three other schemes in previous studies. When large measurement errors exist, the proposed scheme performs better than the three other schemes. When large Ekman balance errors exist, the proposed scheme is better than two of the other schemes. The selection of components of the steady current and tidal constituents also influences the performance of the proposed scheme. Successful estimation of the EVP requires the usage of intense components of the steady current and tidal constituents. With the usage of the intense components, increasing the number of tidal constituents cannot lead to a more accurate estimation of the EVP.