How Does Air-Sea Wave Interaction Affect Tropical Cyclone Intensity? An Atmosphere-Wave-Ocean Coupled Model Study Based on Super Typhoon Mangkhut (2018)

Capturing TC intensity change remains a great challenge for most state-of-the-art operational forecasting systems. Recent studies found TC intensity forecasts are sensitive to three-dimensional ocean dynamics and air-sea interface processes beneath extreme winds. By performing a series of numerical simulations based on hierarchical atmosphere-wave-ocean (AWO) coupling configurations, we showed how atmosphere-ocean and atmosphere-sea wave coupling can affect the intensity of super typhoon Mangkhut (2018). The AWO coupled model can simulate TC-related strong winds, oceanic cold wake, and wind waves with high fidelity. With atmosphere-ocean (AO) coupling implemented, the simulated maximum surface wind speed is reduced by 7 m s(-1) compared to the atmosphere-only run, due to TC-induced oceanic cold wakes in the former experiment. In the fully coupled AWO simulations, the wind speed deficit can be completely compensated by the wave-air coupling effect. Further analyses showed that, in the AWO experiment, two mechanisms contribute to the improvement of TC intensity. First, in the high wind scenario (>28 m s(-1)), the surface drag coefficient reaches an asymptotic level, assisting extreme wind speed to be maintained within the eyewall. Second, the wind speed distribution is modulated and becomes broader; higher wind within the TC area helps to offset the negative effect due to leveling off of the heat exchange coefficient as wind speed increases. Overall, the simulated TC in the AWO run can extract 8-9% more total heat energy from the ocean to maintain its strength, compared to that from the AO experiment.

Automated summary

Capturing the intensity change of typhoons remains challenging for most advanced forecasting systems. Recent studies have found that the three-dimensional dynamics of the ocean and air-sea interface processes play a crucial role in typhoon intensity forecasts. Through numerical simulations, researchers demonstrated how the coupling of atmosphere-ocean and atmosphere-sea waves can affect the intensity of super typhoon Mangkhut in 2018.