Immediate and long-term ocean response to tropical cyclones: turbulent mixing and near-inertial oscillations

Three-dimensional motions powered by intense winds associated with tropical cyclones can drastically transform the properties of the upper ocean. In this work, we use shipboard and autonomous float measurements to reconstruct the three-dimensional fields of temperature, salinity and ocean currents beneath Super Typhoon Mangkhut (Western North Pacific, September 2018) and their subsequent effects. Our diagnosis of advective and diffusive processes agrees well with established theory and shows that heat transfer near the storm was dominated by turbulent mixing and near-inertial internal waves, which ultimately cooled the ocean surface by ~1°C. Lastly, we compare shipboard microstructure measurements made in the same region up to 1 week before and 3 weeks after the storm passed. Turbulent heat fluxes averaged over 12 days suggest that the upper 50 m of the water column warmed at an average rate of 0.32°C/month after the storm. Furthermore, we find evidence that near-inertial motions generated by tropical cyclones transferred ocean heat downwards across 150 m depth at a rate in the order of 1x10⁷ W/km² for weeks after their generation. These analyses provide new insights about the role of tropical cyclones in shaping climate through their effect on ocean heat uptake and subsequent impacts to the global overturning circulation.