The role of enhanced velocity shears in rapid ocean cooling during Super Typhoon Nepartak 2016

Typhoon is a major cause of multiple disasters in coastal regions of East Asia. To advance our understanding of typhoon–ocean interactions and thus to improve the typhoon forecast for the disaster mitigation, two data buoys were deployed in the western North Pacific, which captured Super Typhoon Nepartak (equivalent to Category 5) in July 2016 at distances <20 km from the typhoon’s eye center. Here we demonstrate that the unprecedented dataset combined with the modeling results provide new insights into the rapid temperature drop (~1.5 °C in 4 h) and the dramatic strengthening of velocity shear in the mixed layer and below as the driving mechanism for this rapid cooling during the direct influence period of extremely strong winds. The shear instability and associated strong turbulence mixing further deepened the mixed layer to ~120 m. Our buoys also observed that inertial oscillations appeared before the direct wind influence period.A better understanding of typhoon–ocean interactions is critical for improving typhoon forecasts. Here the authors use data from two buoys that captured Super Typhoon Nepartak and combine it with numerical simulations to reveal the role of enhanced velocity shear in rapid upper-ocean cooling.

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