Enhanced Ocean Mixing During the Passage of Tropical Cyclone.

Tropical cyclones are among the most destructive natural disasters. However, lack of detailed observations and the simplifications inherent in operational ocean models, lead to incomplete knowledge of underlying ocean processes. Using high‐fidelity large‐eddy simulations and moored observations away from the storm track, we show that mutually interacting shear and convective processes, govern the evolving state of the upper ocean. Our simulation agrees well with observed sea surface temperature and sea surface salinity. Shear driven turbulence due to surface wind stress erodes stratification, deepens the ocean mixed layer and transports freshwater into the mixed layer during rain events. Concurrently, surface buoyancy loss also aids in ocean mixing via convective entrainment. The mixing efficiency and the associated eddy diffusivity shows high spatiotemporal variability throughout the water column during cyclone passage. Thus, a better insight into the upper ocean mixing mechanisms is necessary for developing improved mixing parameterizations for tropical cyclone intensity forecasts. Plain Language Summary: Tropical cyclones are among the most destructive natural phenomena on Earth. The powerful winds in a cyclone cause vigorous mixing in the upper ocean, cool the sea surface temperature (SST) and influence cyclone intensification. Using high‐fidelity simulations and observations, we demonstrate the synergy between ocean convection and shear driven processes to change the upper ocean state. Due to temporally varying surface forcings, the upper ocean mixing was also highly variable. Our study provides new insights into the energetics of such an extreme event where both wind stress and surface cooling are present. Key Points: Large‐eddy simulations are performed for the upper ocean during the passage of a cycloneShear and turbulent convection acted in concert to modify the upper ocean propertiesIrreversible mixing and mixing efficiency show high spatiotemporal variability [ABSTRACT FROM AUTHOR]