Wave Influences On Wind Energy Input Into The Ekman Layer In The South China Sea

This thesis is concerned with the wave influences on the wind energy input to the Ekman layer, by incorporating the wave-induced Coriolis-Stokes forcing into the classical Ekman model. Analysis of the energy balance shows that the energy input to the Ekman-Stokes layer through the wind stress and the interaction of the Stokes-drift with planetary vorticity can be divided into two kinds. One kind is the wind energy input, and the other one is the wave energy input caused by the Coriolis-Stokes forcing. Under the assumption that the direction of the wind stress is exactly the same as that of the Stokes-drift, the wave-induced energy input consists of two terms. The first term increases the total energy input to the Ekman-Stokes layer compared with the wind energy input to the pure Ekman layer. The second term transfers the energy input within the Ekman-Stokes layer, but has no contribution to the total energy input. Comparisons of the wave-induced energy input with the wind energy input to the pure Ekman layer are made to show the importance of surface wave influences on the energy input.Theoretical results are used to compute the wind and wave energy input into the Ekman layer in the South China Sea. We first use the third-generation wave model WAVEWATCH III to calculate the surface waves in the South China Sea, where the QSCAT/NCEP wind data with resolution of 0.5×0.5 is used to drive the wave model. Modeling results show that the sea waves in the South China Sea are primarily controlled by wind waves. The wave influences on the wind energy input into the Ekman layer caused by the angle between direction of wind and that of waves can by neglected. Then we use the modeled wave parameters and the wind fields to calculate the wind energy input and the wave-induced energy input in the South China Sea. Distributions of wind and wave-induced energy input into the Ekman layer were found to be homogeneous in most of the areas of the South China Sea. Only in the areas around Taiwan and those in the northern Fillipins are the wind and wave-induced energy input found to significant compared with the other areas.The wave-induced energy input into the Ekman layer is about 5-10% of the wind energy input to Ekman layer without wave effects included. By inclusion of wave effects, the wind energy input was deceased about 5-10%, in comparison with the wind energy input to the pure Ekman layer.From the caculated results from 2000 to 2005, the wind and wave-induced energy input to the Ekman layer are shown to change seasonally. The reason is that the wind and wave-induced energy input are determined by the wind stress and the wind fields in the South China Sea are controlled by Eastern Asia Monsoon.