Wave Effect on the Air-Sea Fluxes during Typhoon Seasons

Transport of heat, momentum, and water mass across the air-ocean interface is usually calculated using the bulk formula. The turbulent exchange coefficients depend on the roughness length z0. The gas transport at the water surface is more complicated than the bulk aerodynamic relation for the heat and momentum transfer. For chemical compounds with reaction time scales longer than the surface layer turbulence time scales, the constant flux layer assumption may be invoked. The flux of the gaseous compound (c) is characterized by a deposition velocity, vd, which is the inverse of the resistances, , (1) where ra is the aerodynamic resistance governing turbulent transport of species c; and rb is the surface resistance, governing the diffusion transport over the laminar sublayer (Geernaert, 1999). Both ra and rb depend on the surface roughness length z0.

Usually, the roughness length z0 is determined regardless of the ocean waves. To investigate the wave effect on the turbulent exchange coefficients for heat, momentum, and water mass and resistances ra and rb for gases, Wavewatch-III implemented to the South China Sea (Chu et al., 2004) is used. The Charnock coefficient for determining z0 depends on the significant wave height. The model is integrated with twice daily NCEP reanalyzed winds for the whole year of 2004 with and without ocean waves. Large difference is found in the exchange coefficients and ra and rb during the typhoon seasons and little difference otherwise. This indicates that the role of ocean waves on the air-sea fluxes should not be ignored during the typhoon seasons. REFERENCES Geernaert, G.L., 1999. Theory of air-sea momentum, heat, and gas fluxes. In: Air-Sea Exchange: Physics, Chemistry, and Dynamics, edited by G.L. Geernaert, Kluwer Academic Publishers, Boston, 25-48.

Chu, P.C., Y. Qi, Y.C. Chen, P. Shi, and Q.W. Mao, 2004. South China Sea wave charcteristics. Part-1: Validation of wavewatch-III using TOPEX/Poseidon data. Journal of Atmospheric and Oceanic Technology, 21, 1718-1733.