Langmuir turbulence under tropical cyclones

Abstract

Langmuir turbulence (LT) is generated by surface waves that tilt vertical vorticity of Eulerian currents into the direction of wave propagation through the Craik-Leibovich vortex force. LT plays an important role in turbulent momentum transport in the ocean surface boundary layer (OSBL) and has been observed even in the tropical cyclone (TC) conditions that characterize extreme wind and complex wave forcing with prevalent wind-wave misalignment. This work utilizes a LT-included large eddy simulation (LES) approach to simulate the upper ocean response, which generates a unique, data set of the response of the OSBL and LT to TCs. The first part of our work assesses the general response of the ocean surface boundary layer and LT to extreme wind and complex wave forcing under TCs. Specifically, our results show that LT is sea-state dependent and significantly enhances turbulent entrainment, inducing greater mixed layer deepening and sea surface cooling. The second part focuses on the spatiotemporal variability of turbulent entrainment under the TC, and investigates different mechanisms that induce greater entrainment in the LT case and the ST case. The third part examines the effects of TC's wind-wave misalignment on LT, particularly the effects on LT's intensity and direction, illustrating that TC's wind-wave misalignment reduces LT intensity but does not affect LT direction.