How does air-sea wave interaction affect tropical cyclone intensity? An
atmosphere-wave-ocean coupled model study based on super typhoon
Mangkhut (2018)
Abstract
Capturing TC intensity change remains a great challenge for most
state-of-the-art operational forecasting systems. Recent studies found
the 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 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
(>28m/s), 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.