Talk Abstact:
Tropical cyclone (TC) intensity is strongly affected by the air-sea heat flux beneath the storm. Therefore, accurate predictions of upper ocean responses (such as mixed layer deepening, upwelling, and sea surface temperature cooling) under TCs are necessary for improving TC intensity forecast. The accurate wind stress which driven upper ocean current needs to be understood more. In this study the wind stress (or the drag coefficient) into the ocean and the sea state dependence of drag coefficient (Cd) under tropical cyclones is investigated. The estimated drag coefficient averaged over all storms is around 2~310-3 for wind speeds 25-55~m/s. The drag coefficient is significantly reduced by misaligned swell when the misalignment angle between the dominant wave direction and the wind direction exceeds about 45o.
For the upper ocean response under TCs, impacts of surface waves (the sea-state dependent Langmuir turbulence, the air-sea momentum flux budget, and the wave-current interactions) are investigated by combining upper ocean observations and a coupled ocean-wave (Modular Ocean Model 6 - WAVEWATCH III) model. The results show that the mixed layer turbulent kinetic energy is significantly enhanced by surface waves (Langmuir turbulence). The results also suggest that the Langmuir turbulence and the other surface wave effects modify the mixed layer deepening and other three-dimensional upper ocean responses.
All seminars this quarter will be in a hybrid format. Recording available upon request.