Mixed Layer Deepening Due to Langmuir Circulation

Abstract

Abstract The interaction between wind-driven Langmuir circulation and preexisting stratification is examined in order to elucidate its role in the deepening of the ocean surface mixed layer. For linear stratification, a numerical model suggests that Langmuir cells initially engulf water and create a homogeneous surface layer. The depth h of this layer can be understood in terms of a Froude number Fr = wdn/(Nh), where wdn is the maximum downwelling velocity generated by Langmuir circulation in homogeneous water and N is the buoyancy frequency. Numerical results show that Fr is a constant ≈ 0.6. Using computed values of wdn, this implies that the rapid mixed layer deepening stops at h = cu*/N in which u* is the water friction velocity and the coefficient c is about 10 for fully developed seas. Alternatively, the deepening is arrested when the buoyancy jump Δb at the mixed layer base reaches about 50u2*/h. The above formula, compared with the Price, Weller, and Pinkel value of 0.65 for the bulk Richar...